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Collection of my tech notes/tips/things-to-remember/flash-cards
Raw
notes.json
[
{
"id": 100,
"description": "vim - pull current word onto search or command line",
"tags":[
"vim",
"keyboard",
"shortcuts"
],
"contents":[
"<Ctrl-R><Ctrl-W> - to pull <cword> onto search or command line",
"e.g. :vsplit <Ctrl-R><Ctrl-W> // will insert the name under cword."
]
},
{
"id": 99,
"description": "vim - set markers",
"tags":[
"vim",
"keyboard",
"shortcuts"
],
"contents":[
"m a - to set a marker at the current position",
"` a - to go to the marked position"
]
},
{
"id": 98,
"description": "vim - filename completion",
"tags":[
"vim",
"keyboard",
"shortcuts"
],
"contents":[
"In insert mode, press Ctrl-X followed by Ctrl-F to trigger filename completion",
"If the text under cursor is a path, filename completion will show the list of files under that path"
]
},
{
"id": 97,
"description": "vim - line completion",
"tags":[
"vim",
"keyboard",
"shortcuts"
],
"contents":[
"In insert mode, press Ctrl-X followed by Ctrl-L to trigger line completion",
"This will list all the lines matching the text entered in the current line",
"Scroll up/down to select the line and insert"
]
},
{
"id": 96,
"description": "bash - shuffle lines of output with shuf utility",
"tags":[
"bash",
"commands",
"shell",
"tools"
],
"contents":[
"# shuf command generates random permutations of input lines and writes to standard out",
"# some_command | shuf -n 1 # to select 1 random line from the output of some_command",
"# note: shuf is available as part of GNU CoreUtils package"
]
},
{
"id": 95,
"description": "vim - resize split window panes",
"tags": [
"vim",
"keyboard",
"shortcuts",
"productivity"
],
"contents": [
"# To resize the current pane up/down in a horizontal split",
"# Ctrl-W +/-",
"# To resize the current pane up/down by number of lines",
"# Ctrl-W <number> +/-",
"# To resize the current pane left/right in a vertical split",
"# Ctrl-W </>",
"# To resize the current pane left/right by number of columns",
"# Ctrl-W <number> </>"
]
},
{
"id": 94,
"description": "tmux - resize panes with keyboard shortcuts",
"tags": [
"tmux",
"keyboard",
"shortcuts",
"productivity"
],
"contents": [
"# To resize the current pane up/down/left/right",
"# Press prefix key followed by Modifier-key+Up/Down/Left/Right to resize in respective direction",
"# resizes by 5 rows/columns by default",
"# My prefix key is Ctrl+L (whereas Ctrl+B is the default). Modifier key is option key",
"# bindkey -r allows the key to be bound in repeat mode. So pressing twice M-Up after the prefix key (Ctrl+L) moves the pane up by 10 (2*5) rows",
"# bind-key -r M-Up resize-pane -U 5"
]
},
{
"id": 93,
"description": "vscode - insert multi line cursor in mac",
"tags": [
"vscode",
"keyboard",
"shortcuts"
],
"contents": [
"Cmd + Option + Up/Down - to insert cursor at the beginning of lines up or below",
"Option + Shift + I - to insert cursor at the end of the selected lines"
]
},
{
"id": 92,
"description": "gcp - cloud functions: manage functions with gcloud CLI",
"tags": [
"commands",
"gcp",
"cloud functions"
],
"contents": [
"# To list deployed functions",
"gcloud functions list",
"",
"# To deploy new functions or update an existing function",
"gcloud functions deploy",
"",
"# example: deploy a function with source code from local machine, python3.11 as runtime and pubsub topic as trigger",
"# To set up google cloud functions with environment variables specified in a yaml file, use `--env-vars-file` option",
"",
" gcloud functions deploy my-gcp-func \\",
" --gen2 \\",
" --region=us-central1 \\ # region to deploy",
" --runtime=python311 \\ # python 3.11 as the runtime",
" --source=. \\ # deploy with source code from current directory on the local machine",
" --entry-point=cloud_event_handler \\ # entry point function in main.py",
" --trigger-topic=pubsub-topic \\",
" --env-vars-file .env.yaml # file with list of environment variables to set up",
"",
"# Delete a cloud function",
"gcloud functions delete my-gcp-func",
"",
"# View logs from a cloud function",
"gcloud functions logs read my-gcp-func"
]
},
{
"id": 91,
"description": "gcp - pubsub: interact with pubsub through gcloud CLI",
"tags": [
"commands",
"gcp",
"pubsub"
],
"contents": [
"# To list subscribers of a topic",
"gcloud pubsub topics list-subscriptions my-pubsub-topic",
"",
"# To publish a message to pubsub topic",
"gcloud pubsub topics publish pubsub-topic1 --message \"hello,world\""
]
},
{
"id": 90,
"description": "Download compressed data and uncompress with CURL",
"tags": [
"linux",
"commands",
"curl"
],
"enabled": true,
"contents": [
"Add `--compressed` option to curl to auto decompress data after download.",
"e.g. curl --compressed https://api.stackexchange.com/2.2/sites"
]
},
{
"id": 89,
"description": "tempfile in Python",
"tags": [
"python",
"programming"
],
"enabled": true,
"contents": [
"Use tempfile.NamedTemporaryFile() callable to have a temporary file with a visible name",
"By default, file is opened in binary mode and is deleted on closing",
"Use \"w+\" to open in text mode.",
"Also works with context manager.",
">>> with tempfile.NamedTemporaryFile() as fp:",
"... fp.write(b'Hello world!')",
"... fp.seek(0)",
"... fp.read()",
"b'Hello world!'"
]
},
{
"id": 88,
"description": "Python: Get home directory",
"tags": [
"programming",
"python"
],
"enabled": true,
"contents": [
"Class method pathlib.Path.home() returns a new path object",
"representing user home directory (similar to os.path.expanduser(\"~\")",
"Path object also supports / operator, so Path.home()/subdir/file is also possible"
]
},
{
"id": 87,
"description": "Find which shell I am in",
"tags": [
"linux",
"shell"
],
"contents": [
"Run \"echo $SHELL\" ",
"root@88a325681e8c:/# echo $SHELL",
"/bin/bash"
]
},
{
"id": 86,
"description": "Find system information from command line",
"tags": [
"linux",
"shell"
],
"contents": [
"uname, uname -a",
"root@88a325681e8c:/# uname -a",
"Linux 88a325681e8c 4.9.184-linuxkit #1 SMP Tue Jul 2 22:58:16 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux",
""
]
},
{
"id": 85,
"description": "Find disk usage of directory and files with \"du\"",
"tags": [
"linux",
"shell",
"tools"
],
"contents": [
"du -a - display an entry for each file in the directory",
"du -c - display a grand total",
"du -h - display info in human readable form (take optional unit suffixes (-m for MB, -g for GB))",
"du -d <depth> - stop at given depth level"
]
},
{
"id": 84,
"description": "Access last executed command in shell",
"tags": [
"linux",
"shell"
],
"contents": [
"Use \"!!\" to access the last ran command"
]
},
{
"id": 83,
"description": "Get status of last command/process",
"tags": [
"linux",
"shell"
],
"contents": [
"$? - return the status of the last command ran in shell"
]
},
{
"id": 82,
"description": "Access arguments from last command",
"tags": [
"linux",
"programming",
"shell"
],
"contents": [
"!^ - First argument",
"!$ - Last argument",
"!* - All arguments"
]
},
{
"id": 81,
"description": "Colorize ls output",
"tags": [
"linux",
"shell"
],
"contents": [
"ls --color=always (on most Linux)",
"ls -G (on macOS)"
]
},
{
"id": 80,
"description": "List files with their disk usage",
"tags": [
"shell",
"linux"
],
"contents": [
"$ ls -lash",
"Shows a **long** listing of **all** files along with their ",
"**actual file size in number of blocks** (typically 512 bytes) and ",
"file size in **human readable** form (e.g B for bytes, K for kilobytes, G for gigabytes etc)"
]
},
{
"id": 79,
"description": "Supress newline character in shell",
"tags": [
"shell",
"linux"
],
"contents": [
"`echo -n` - skips the trailing newline character",
"Note: some shells do not support -n option.",
"For portability, use printf instead."
]
},
{
"id": 78,
"description": "Sort lines in shell",
"tags": [
"linux",
"shell"
],
"contents": [
"sort - command to sort lines of text or binary data from standard input or a file descriptor.",
"Default order: lexicographic",
"-k <column number> - sort by a specific key",
"-n - sort numerically",
"-s - keep the sorting order stable"
]
},
{
"id": 77,
"description": "Generate sequence of numbers",
"tags": [
"linux",
"shell"
],
"contents": [
"seq - Generate sequence of numbers",
"starts from 1 and increments 1 by default",
"$ seq 4 // generate 1 to 4",
"$ seq 10 2 20 // generate 10 to 20, increment by 2"
]
},
{
"id": 76,
"description": "Find system calls used by a program",
"tags": [
"linux",
"shell",
"programming"
],
"contents": [
"strace <program>"
]
},
{
"id": 75,
"description": "Find disk usage of files and directories",
"tags": [
"linux",
"shell"
],
"contents": [
"du - find disk usage of a directory and its files",
"-a - display an entry for each file in the directory",
"-c - display a grand total",
"-h - display info in human readable form (take optional unit suffixes: -m for MB, -g for GB)",
"-d <depth> - stop at given depth level"
]
},
{
"id": 74,
"description": "Where man pages are stored?",
"tags": [
"shell",
"linux"
],
"contents": [
"Pages are searched first in the path given by option `-M` if specified.",
"If `-M` is not specified, then the path specified in `MANPATH` is looked up.",
"If neither `-M` nor `MANPATH` is specified, then the path to man pages is inferred from the config file.",
"In general, the default set of man pages live in `/usr/share/man/`",
"Applications can install in other paths too and update the `MANPATH` accordingly.",
"The location of the config file can differ based on the distribution.",
"/private/etc/man.conf - in macOS Mojave",
"/etc/man.config - in many linux distributions"
]
},
{
"id": 73,
"description": "Convert epoch seconds into date",
"tags": [
"linux",
"commands",
"shell",
"datetime"
],
"contents": [
"% date -r <seconds> # macOS",
"$ date -d @<seconds> # on most linux",
"$ date +%s # display current time in epoch seconds"
]
},
{
"id": 72,
"description": "Toggle reader mode in Safari",
"tags": [
"macOS",
"shortcuts",
"safari"
],
"contents": [
"`Cmd + Shift + R` - toggles reader mode on supported sites"
]
},
{
"id": 71,
"description": "Find files modified in last x minutes or x days",
"tags": [
"shell",
"find",
"linux",
"commands"
],
"contents": [
"`$ find . -mmin -60` - find files modified in the last 60 minutes in current directory",
"`$ find . -mtime -2` - find files modified in the last 48 hours in current directory"
]
},
{
"id": 70,
"description": "Find files accessed in last x minutes or x days",
"tags": [
"shell",
"find",
"linux",
"commands"
],
"contents": [
"`$ find . -amin -60` - find files modified in the last 60 minutes in current directory",
"`$ find . -atime -2` - find files modified in the last 48 hours in current directory"
]
},
{
"id": 69,
"description": "sshpass - specify password for ssh/scp login non-interactively",
"tags": [
"shell",
"linux",
"commands",
"scp"
],
"contents": [
"`sshpass -p <password> ssh user@host \"command to run\"` - Use the specified password to connect using ssh",
"`sshpass -p <password> scp <source> <destination>` - Use the specified password to connect using scp",
"`SSHPASS=password sshpass -e ssh user@host command` - Take the password from the environment variable SSHPASS"
]
},
{
"id": 68,
"description": "scp - some helpful options (pqr)",
"tags": [
"shell",
"linux",
"commands",
"scp"
],
"contents": [
"`-p` - Preserve modification times, access times, and modes",
"`-q` - Quiet mode: disables the progress meter as well as warning and diagnostic messages from ssh",
"`-r` - Recursively copy entire directories"
]
},
{
"id": 67,
"description": "ssh options - Ignore host key checking",
"tags": [
"ssh",
"shell",
"commands",
"options"
],
"contents": [
"`-o StrictHostKeyChecking=no` - automatically add new host keys to users known hosts file. Often not needed in controlled environments",
"`-o UserKnownHostsFile=/dev/null` - Use /dev/null instead of the default file (~/.ssh/known_hosts)",
"Set `StrictHostKeyChecking no` in .ssh/config under `Host <hostname>` to apply this to per hosts"
]
},
{
"id": 66,
"description": "bash - a quick note on arrays",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"arr=() # Create empty array",
"arr+=(5) # Append a number to array",
"arr+=(xyz) # Append a text to array; arrays can have numbers and strings",
"${arr[@]} # Get all items from the array",
"${!arr[@]} # Get all indices of the array. Index starts at 0",
"${arr[3]} # Get the fourth item from the array",
"${arr} # Get first item from the array. Equivalent to ${arr[0]}",
"${arr[@]:i:n} # Get n elements starting at index i",
"arr=( $(cmd) ) # Save output of a command into an array",
"# Sample for loop",
"for item in ${arr[@]};do",
" echo $item",
"done"
]
},
{
"id": 65,
"description": "vim - show relative and absolute file path",
"tags": [
"vim",
"programming",
"editor",
"shortcuts"
],
"contents": [
"Ctrl+G - shows the relative path of the current file",
"{n}Ctrl+G - shows the relative path of the nth file in the buffer",
"1Ctrl+G - shows the absolute path of the current file"
]
},
{
"id": 64,
"description": "vim - set/toggle option",
"tags": [
"vim",
"shortcuts",
"editor",
"programming"
],
"contents": [
":set <option> - switches on a toggle option",
":set <option>! - toggles the option",
":set <option>? - shows the value of option",
"e.g :set nu - turns on the line number, :set nonumber - turns off the line number",
":set nu! toggles the line number on or off,"
]
},
{
"id": 63,
"description": "bash: read inputs",
"tags": [
"bash",
"programming",
"shell"
],
"contents": [
"read var # gets the input from the user and assings to the variable \"var\"",
"read -p \"Prompt\" var # shows the prompt message",
"read -ps \"Prompt\" var # shows the prompt message, but keeps the input hidden.",
"# E.g.",
"# $ read -p \"Select: \" choice",
"# Select: 1",
"# $ echo $choice",
"# 1"
]
},
{
"id": 62,
"description": "vscode: terminal shortcuts",
"tags": [
"vscode",
"shortcuts",
"terminal",
"productivity"
],
"contents": [
"`Cmd + \\` - keyboard shortcut to split the terminal vertically",
"`Cmd + Option + Left` - focus to the window on the left",
"`Cmd + Option + Right` - focus to the window on the right",
"`Cmd + j` - hide the terminal window and focus on active editor group"
]
},
{
"id": 61,
"description": "bash: arithmetic with let",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"let # evaluates each argument as an arithmetic expression",
"let a=1+9 # assigns a=10",
"# If spacing needed for better readability, enclose the expression between quotes",
"let \"b = 2 + 8\" # assigns b=10",
"# Take values from variables",
"let c=$a+$b # assigns sum of a and b to c",
"# No escaping needed for *",
"let \"d = $a * $b\" # assigns product of a and b to d",
"let d++ # increment d by 1 and assign to d"
]
},
{
"id": 60,
"description": "bash: arithmetic with expr",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"expr 2 + 7 # evaluate the expression and writes to standard output. Spaces are needed between the tokens",
"# multiplication operator * need to be escaped",
"expr 7 * 3 # results in syntax error",
"expr 7 \\* 3 # evaluates to 21",
"e=$(expr 2 + 7) # evaluate the expression and assign. Similar to $((expression))",
"expr 2+7 # prints the expression as is without evaluating",
"expr \"2 + 7\" # prints the expression as is without evaluating even with quotes"
]
},
{
"id": 59,
"description": "bash: arithmetic expansion",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"# $((expression)) - evaluates the expression and substitutes the result.",
"echo $((3+5)) # prints 8",
"# spaces are totally fine",
"f=$((4 + 4)) # evaluate the expression and assign the value to a variable",
"g=$((f * 2)) # variables inside the expression need not be specified with a preceding $ sign",
"echo $((g--)) $((g++)) # increment, decrement",
"echo ((g += 5) # assignment operators (= *= /= %= += -= <<= >>= &= ^= |=) are also supported"
]
},
{
"id": 58,
"description": "ffmpeg2 - Convert video to gif",
"tags": [
"tools",
"ffmpeg"
],
"contents": [
"# Supports multiple input file formats",
"# -r <frame rate>",
"# -vf <filter_graph> # e.g. -vf scale=w:hP",
"ffmpeg2 -i <input file> -r 10 output.gif",
"# set width to 320px and set height based on the width keeping the aspect ratio",
"ffmpeg2 -i <input file> -r 10 -vf scale=320:-1 output.gif"
]
},
{
"id": 57,
"description": "bash: print values in hex",
"tags": [
"bash"
],
"contents": [
"printf \"0x%x\\n\", 369098752 # prints the value in hex format. e.g. 0x16000000"
]
},
{
"id": 56,
"description": "vim: yank shortcuts",
"tags": [
"vim",
"shortcuts"
],
"contents": [
"`yw` - copy from current to start of the next word",
"`yb` - copy from current to beginning of the current word",
"`y$` - copy till the end of the line",
"`y0` - copy till the start of the line",
"`{n}Y` - copy n number of lines",
"`{n}yy` - copy n number of lines"
]
},
{
"id": 55,
"description": "C: Get system time in epoch seconds (number of seconds since 1970-01-01 00:00:00 +0000 (UTC))",
"tags": [
"c",
"programming",
"datetime"
],
"contents": [
"time_t curtime = time(NULL); // time() included from time.h",
"(void)time(&curtime); // also sets the seconds in the input buffer if given",
"// can also get the time in microsecond granularity with gettimeofday",
"struct timeval tm;",
"struct timezone tz",
"(void)gettimeofday(&tm, &tz); // included from sys/time.h",
"// tm.tv_sec - epoch time in seconds",
"// tm.tv_usec - microseconds",
"// tz.tz_dsttime - is Daylight Savings on?",
"// tz.tz_minuteswest - number of minutes from the GMT",
"printf(\"secs=%lu, msecs=%d, is_dst=%d, minutes_from_gmt=%d\n\", tm.tv_sec, tm.tv_usec, tz.tz_dsttime, tz.tz_minuteswest);",
"printf(\"timestamp=%s\", ctime(&tm.tv_sec)); // get clock time as a readable string",
"// ctime returns a pointer to statically allocated buffer holding the stamp.",
"// Subsequent calls to ctime() would overwrite the buffer. Use ctime_r() to write the string to user provided buffer instead."
]
},
{
"id": 54,
"description": "bash: display information about a command type",
"tags": [
"shell",
"bash",
"programming"
],
"contents": [
"type arg # arg can be a command, function, aliases an built-ins",
"type -a arg # display all locations containing an executable named NAME",
"type -t arg # output a single word which is one of alias, keyword, function, builtin, file",
"# e.g.",
"ubuntu@ubuntu-lts:~$ os_release()",
"> {",
"> cat /etc/os-release",
"> }",
"ubuntu@ubuntu-lts:~$ type -t os_release",
"function",
"ubuntu@ubuntu-lts:~$ type -a os_release",
"os_release is a function",
"os_release ()",
"{",
" cat /etc/os-release",
"}"
]
},
{
"id": 53,
"description": "regex: filter ipv4 address",
"tags": [
"linux",
"tools",
"regex"
],
"contents": [
"# regex pattern to filter IPv4 addresses",
"# upto 3 digits followed by ., repeated 3 times and up to 3 digits",
"# this is too generic. so invalid IPs like 333.232.444.999 would also be considered valid",
"ifconfig | egrep -o '([0-9]{1,3}\\.){3}[0-9]{1,3}'",
"# To search for only valid IP addr and output only the IP addr",
"ifconfig | egrep -o '((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)'",
"# Skip localhost and subnet masks",
"ifconfig | egrep -o '((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)' | egrep -v '^255|127.0.0.1'"
]
},
{
"id": 52,
"description": "sed - Get a line or range of lines",
"tags": [
"linux",
"tools",
"shell",
"sed"
],
"contents": [
"# Get contents of line number n from file",
"# -n - tells sed not to print the lines unless explicity requested",
"# 'p' - print command",
"# 'q' - quit sed",
"sed -n '10p' # print line number 10, but will continue processing the rest of the file too",
"sed -n '10p;11q' # print line number 10 and quit processing",
"sed -n '5,10p;11q' # print line number from 5 to 10 and quit processing"
]
},
{
"id": 51,
"description": "grep - find empty lines",
"tags": [
"linux",
"shell",
"tools",
"grep"
],
"contents": [
"grep -n '^$' <file> # print line numbers of empty lines in the given file"
]
},
{
"id": 50,
"description": "vim - clear all trailing whitespaces",
"tags": [
"linux",
"vim",
"tools"
],
"contents": [
"\" function to clear trailing white spaces",
"fun! TrimTrailingWhiteSpace()",
" let l:save = winsaveview()",
" keeppatterns %s/\\s\\+$//e",
" call winrestview(l:save)",
" \" without saving and restoring the view, the cursor",
" \" moves to the line of the last search result where",
" \" the edit is made",
"endfun",
"",
"\" Use a shortcut to invoke the function",
"\" for e.g. I use the leader key \\ followed by w",
"\\ + w to clear the trailing whitespace",
":noremap <Leader>w :call TrimTrailingWhiteSpace()<CR>"
]
},
{
"id": 49,
"description": "openssl - show certificate validity",
"tags": [
"tools",
"openssl"
],
"contents": [
"# show notBefore and notAfter date of the given certificate",
"openssl x509 -noout -startdate -enddate -in <certificate>",
"# print all details of the certificate in text format",
"openssl x509 -noout -text -in root_ca.crt"
]
},
{
"id": 48,
"description": "Python: Get host name of the system",
"tags": [
"python",
"scripts"
],
"contents": [
"import socket",
"print(socket.gethostname()) # print hostname to stdout"
]
},
{
"id": 47,
"description": "Python: Get interpreter history",
"tags": [
"python",
"programming"
],
"contents": [
"# History of commands run in python interpreter are cached at $HOME/.python_history",
"# readline module provides the methods to access the entries from the underlying history buffer",
"# readline.get_current_history_length() returns the current number of items",
"# readline.get_history_item(index) returns the item at the given index",
"import readline",
"history_length = readline.get_current_history_length()",
"for i in range(1, history_length):",
" print(readline.get_history_item(i)"
]
},
{
"id": 46,
"description": "Python: Startup scripts for the interactive sessions",
"tags": [
"programming",
"python"
],
"contents": [
"# If the environment variable PYTHONPATH points to a readable file",
"# commands in that file are executed before the prompt is given to the",
"# user in interactive mode",
"# e.g. export PYTHONPATH=$HOME/.pythonrc.py"
]
},
{
"id": 45,
"description": "vim - switching between vim buffers",
"tags": [
"programming",
"productivity",
"vim",
"editor"
],
"contents": [
":buffers or :ls or :files - list open buffers",
":bn, :bnext - go to next buffer",
":bp, :bprev - go to previous buffer",
":b <filename> - go to buffer with the given file name",
":b ex - open buffer with filename starting with ex",
"Ctrl-6 - toggle between current and last buffer"
]
},
{
"id": 44,
"description": "vim - search patterns using vimgrep",
"tags": [
"vim",
"productivity",
"editor",
"programming"
],
"contents": [
":vimgrep /{pattern}/[g][j] {filenames} - search pattern in given files and update quicklist (aka error list)",
" - {pattern} follows vim regex pattern",
" - g - return all matches",
" - j - update quick list only. do not jump to the first match.",
" vimgrep loads the file into memory, so can be slow for large files",
":cn - go to next match in the quick list",
":cp - go to previous match in the quick list",
":cc n - go to nth match in the quick list",
":clist [from] [to] - list all errors that are valid",
":copen - open a window to show list of errors"
]
},
{
"id": 43,
"description": "vim - misc shortcuts",
"tags": [
"vim",
"editor",
"productivity"
],
"contents": [
"q: - (in command mode) to list the commands in chronological order. Allows editing too",
":history - list commands from history table",
":set <setting-name>? - show the current value of the given setting",
":echo &<setting-name> - show the current value of the given setting",
":echo &cmdwinheight - show the current value of cmdwinheight",
":set! all - show all settings, one per line",
":set cmdwinheight=10 - set the height of the command history window to 10. Default is 7"
]
},
{
"id": 42,
"description": "git - revert changes to a single file",
"tags": [
"git",
"shortcuts"
],
"contents": [
"git checkout [commit ID] -- /path/to/your/file # Defaults to HEAD if no commit ID is specified"
]
},
{
"id": 41,
"description": "Python - register functions to be called at exit",
"tags": [
"python",
"programming"
],
"contents": [
"import atexit",
"atexit.register(func1) # register func1 to be called when interpreter exits (some exceptions apply)",
"atexit.register(func2, arg1, arg2) # func2(arg1, arg2) will be called at exit",
"atexit.register(func3, arg1=\"foo\", arg2=\"bar\") # func3(arg1=\"foo\", arg2=\"bar\") will be called at exit",
"@atexit.register # use decorator to register functions. Can't be used with functions with args",
"def func4():",
" print(\"Bye\")",
"# registered functions are called in last-in-first-out order"
]
},
{
"id": 40,
"description": "Makefile - automatic variables within the recipe",
"tags": [
"programming",
"makefile"
],
"contents": [
"# $@ - file name of the target of the rule",
"# $< - name of the first prerequisite",
"# $? - names of all prerequisites that newer than target",
"# $^ - name of all prerequisites",
"# NOTE: these variables are available only within the recipe of a target"
]
},
{
"id": 39,
"description": "Python: pretty print python data structures",
"tags": [
"python",
"programming"
],
"contents": [
"# pprint module provides a way to pretty print arbitrary",
"# data structures including the built in data types.",
"import pprint",
"pprint.print(mydict)",
"# pprint.print defaults to 80 columns per line.",
"# depth and indent level can be adjusted too"
]
},
{
"id": 38,
"description": "shell - delimit by consecutive whitespaces/tabs in cut",
"tags": [
"programming",
"shell"
],
"contents": [
"# -w option to cut filters the text using whitespaces and tabs as delimiters",
"# consecutive white spaces and tabs counted as single field",
"cut -w -f 4-6 # filter the lines by whitespaces/tab and output fields 4 through 6",
"# NOTE: This is available only in cut implementation conforming to (\u201cPOSIX.2\u201d)",
"# supported on macOS"
]
},
{
"id": 37,
"description": "macOS - show emoji keyboard",
"tags": [
"macOS",
"keyboard",
"shortcuts"
],
"contents": [
"Ctrl + Cmd + Spacebar -> to bring up emoji keyboard \ud83d\ude0e"
]
},
{
"id": 36,
"description": "ssh - disable login banner",
"tags": [
"linux",
"ssh",
"productivity"
],
"contents": [
"# create /home/$USER/.hushlogin to suppress ssh login banner for a particular user"
]
},
{
"id": 35,
"description": "golang - discard all writes",
"tags": [
"programming",
"golang"
],
"contents": [
"io.Discard is equivalent /dev/null",
"All writes to io.Discard succeeds without doing anything"
]
},
{
"id": 34,
"description": "shell - get specific line in a file",
"tags": [
"programming",
"shell"
],
"contents": [
"# there are multiple ways to do this. I find sed easier than others",
"# sed -n 'np' file - to get nth line a file",
"sed -n '10p' file # to get 10th line in a file"
]
},
{
"id": 33,
"description": "shell - set the positional parameters",
"tags": [
"programming",
"shell"
],
"contents": [
"# Set the values of the positional parameters to script, bash functions",
"# set foo to $1, bar to $2",
"set -- foo bar"
]
},
{
"id": 32,
"description": "jq - filter keys with special characters",
"tags": [
"json",
"programming",
"tools",
"jq"
],
"contents": [
"# If keys in json data contain special characters, the keys need to be enclosed in \"\" in the jq filter string",
"# e.g. ",
"kubectl get secrets cluster-xyz -o json | jq -r '.data.\"tls.crt\"' | base64 --decode"
]
},
{
"id": 31,
"description": "tmux - send commands to multiple panes at the same time",
"tags": [
"tmux",
"programming",
"tools",
"shortcuts"
],
"contents": [
"Prefix key + : - to bring command prompt",
":setw synchronize-panes on - to turn on command synchronization",
":setw synchronize-panes off - to turn off command synchronization",
"The default prefix is Ctrl-B. I use Ctrl-L"
]
},
{
"id": 30,
"description": "du - display the size of directories, skip subdirectories",
"tags": [
"linux",
"shell",
"commands",
"tools"
],
"contents": [
"# du displays the size of the subdirectories as well by default.",
"du -sch dir1 dir2 #display size of dir1 and dir2 and the grand total in human readable form"
]
},
{
"id": 29,
"description": "macOS/finder - keyboard shortcuts",
"tags": [
"macOS",
"keyboard",
"shortcuts"
],
"contents": [
"Cmd + Shift + N - to create a new folder",
"Cmd + Delete - to delete a file or folder"
]
},
{
"id": 28,
"description": "gdb - dump backtrace of all threads",
"tags": [
"programming",
"gdb",
"debugging"
],
"contents": [
"#dump backtrace of all threads",
"thread apply all backtrace"
]
},
{
"id": 27,
"description": "git - undo uncommited local changes to a specific file",
"tags": [
"programming",
"git"
],
"contents": [
"# To undo uncommitted local changes to a specific file.",
"# This command overwrites the current version of filename",
" with the version from remote branch",
"<filename> is specified as per path spec. See https://git-scm.com/docs/gitglossary#Documentation/gitglossary.txt-aiddefpathspecapathspec",
"# git checkout -- filename"
]
},
{
"id": 26,
"description": "git - add a remote branch and set local branch to push to new remote branch",
"tags": [
"programming",
"git"
],
"contents": [
"# The workflow goes like this",
"# git checkout -b <a_new_branch>",
"# make edits..make commits..time to push to remote branch and/or create PR",
"# git push --set-upstream origin <a_new_branch>",
"# git push"
]
},
{
"id": 25,
"description": "git - deleting a branch",
"tags": [
"programming",
"git"
],
"contents": [
"git branch -d <branch> # to delete local branch",
"git branch -D <branch> # to force delete local branch",
"git push <remote> --delete <remote-branch-name> # to delete remote branch.",
"# e.g. git push origin --delete pr123456"
]
},
{
"id": 24,
"description": "vim - open multiple files in tabs",
"tags": [
"programming",
"vim",
"editor",
"productivity"
],
"contents": [
"# use option -p with vim to open multiple files in tabs",
"vim -p file1 file2 file3"
]
},
{
"id": 23,
"description": "docker - display only repo and tag info in docker images",
"tags": [
"docker",
"commands",
"tools"
],
"contents": [
"# to display only image repo and tag information in 'docker images' command",
"# useful when including the output in other commands such as docker run",
"docker images --format '{{.Repository}}:{{.Tag}}'"
]
},
{
"id": 22,
"description": "markdown - insert multi line quote",
"tags": [
"markdown",
"editor"
],
"contents": [
"`>` - inserts a block quote in markdown.",
"Add two spaces at the end of line to make a multi line quote",
"> Stay hungry",
"> Stay foolish",
"will produce | Stay hungry Stay foolish",
"> Stay hungry ",
"> Stay foolish ",
"will produce",
"| Stay hungry",
"| Stay foolish"
]
},
{
"id": 21,
"description": "valgrind - check mem leaks, double free, double free",
"tags": [
"c",
"programming",
"tools",
"valgrind"
],
"contents": [
"valgrind --tool=memcheck --leak-check=yes --track-origins=yes <executable>"
]
},
{
"id": 20,
"description": "tmux - reclaim the entire window during attach",
"tags": [
"tmux",
"terminal",
"productivity"
],
"contents": [
"# After attaching to a session, tmux can sometimes fill the window with L-shaped ",
"# ....., leaving very little space for the actual client. This can happen if the ",
"# session is attached elsewhere. Use the flag -d to detach the existing session.",
"$ tmux attach-session -d"
]
},
{
"id": 19,
"description": "Python - Get current time with timezone info",
"tags": [
"python",
"programming",
"datetime"
],
"contents": [
"# Use pytz.timezone to add timezone info when dealing with datetime",
">>> from datetime import datetime",
">>> from pytz import timezone",
">>> now = datetime.now(tz=timezone(\"EST\"))",
">>> now",
"datetime.datetime(2022, 11, 11, 12, 6, 3, 779069, tzinfo=<StaticTzInfo 'EST'>)",
">>> # another way to do the same",
"... ",
">>> eastern = timezone(\"US/Eastern\")",
">>> now = eastern.localize(datetime.now())",
">>> now.tzinfo",
"<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>"
]
},
{
"id": 18,
"description": "Python - using pathlib for quick actions with files",
"tags": [
"python",
"programming",
"io"
],
"contents": [
"# for simple actions like opening a file and just reading some text",
"# or writing few lines of text in a string, pathlib.Path can be a great option",
"# it abstracts away the usual workflow of opening a file, writing and closing",
"# into convenient functions",
">>> from pathlib import Path",
">>> myfile = Path(\"foobar.txt\")",
">>> myfile.write_text(\"foobar\")",
"6",
">>> myfile.read_text()",
"'foobar'"
]
},
{
"id": 17,
"description": "shell - list only directories",
"tags": [
"shell",
"commands",
"shortcuts",
"linux"
],
"contents": [
"# ls */ - lists directories recursively",
"# ls -d */ - lists only directories in current directory",
"ls -d */",
"# another way to do this, but in long listing format",
"# ls -l | grep ^d"
]
},
{
"id": 16,
"description": "tools - list contents of a tar/tar.gz archive",
"tags": [
"shell",
"tools",
"productivity",
"shortcuts"
],
"contents": [
"# to simply list contents of a tar archive without unarchiving it",
"tar -tvf file.tar # list conents of .tar file",
"tar -tzvf file.tar.gz # list contents of zipped tar",
"tar -jtvf file.tar.bz2 # list contents of tar.bz2 file",
"tar -tvf file.tar '*.cpp' # search for .cpp files in the archive"
]
},
{
"id": 15,
"description": "Python - read contents pointed by a URL",
"tags": [
"python",
"programming"
],
"contents": [
"# read contents of a link using requests",
"r = requests.get(\"https://someurl.com/somefile.json\")",
"# gets a response object",
"r.text # to read the contents as a text",
"r.json() # to return a json dict of the data pointed by the url"
]
},
{
"id": 14,
"description": "Python - validate a string is valid URL or not",
"tags": [
"python",
"programming",
"productivity"
],
"contents": [
"# using validators package",
"import validators",
"# validators.url() returns true if the url is valid",
"is_url = validators.url(\"https://someurl.com\")"
]
},
{
"id": 13,
"description": "Python - process shell command result line by line",
"tags": [
"python",
"programming",
"shell",
"snippets"
],
"contents": [
">>> import subprocess",
">>> cmd_result = subprocess.run(\"ls -l\".split(), text=True, capture_output=True)",
">>> # split the output by newline to process each line",
">>> for line in cmd_result.stdout.split(\"\n\"):",
"... if line.startswith('d'):",
"... # processing only directories",
"... print(line)",
"...",
"drwxr-xr-x 1 root root 4096 Nov 9 08:42 man1",
"drwxr-xr-x 2 root root 4096 Nov 9 08:42 man5",
"drwxr-xr-x 2 root root 4096 Nov 9 08:07 man8"
]
},
{
"id": 12,
"description": "shell - get absolute path of a link",
"tags": [
"bash",
"shell",
"shortcuts",
"programming"
],
"contents": [
"$ readlink -f path-to-link # recursively resolve and return the canononical path of the link"
]
},
{
"id": 11,
"description": "vscode - cmd shortcut to jump to bracket",
"tags": [
"vscode",
"keyboard",
"shortcuts"
],
"contents": [
"\"Cmd + Shift + \\\" to go to the end / beginning of a code block",
"If the middle of a block, it jumps to the end of the block."
]
},
{
"id": 10,
"description": "C - Generate random int",
"tags": [
"c",
"cpp",
"snippets"
],
"contents": [
"// Generate random ints with rand() in the range of 0 to RAND_MAX (defined in stdlib.h)",
"// RAND_MAX is set to 2147483647 in case of mac",
"printf(\"a random number:%d\", rand());",
"// Seed with srand(unsigned seed_value), often the seed_value is the current timestamp",
"srand(time(NULL));",
"printf(\"another random number:%d\", rand());"
]
},
{
"id": 9,
"description": "shell - sum numbers from stdin",
"tags": [
"shell",
"commands",
"tools"
],
"contents": [
"# Ways to sum up numbers from stdin or from piped output from previous commands",
"# Using paste command",
"$ echo somefile | paste -s -d+ | bc",
"$ cat nums | paste -sd+ - | bc",
"# using awk.. substitute $1 with the actual column number",
"$ cat nums | awk '{sum += $1} END {print sum}'"
]
},
{
"id": 8,
"description": "cpp - google style guide - typenames, filenames, variables",
"tags": [
"cpp",
"programming",
"code"
],
"contents": [
"# filenames - all lower case and can include `-` or `_`. e.g. my_class.h my_class.cc",
"# typenames - in PascalCase - applies to classes, structs, type alias, enums and type templates",
"# variables - all lower case, words separated by `_`. local variables, function parameters, class members"
]
},
{
"id": 7,
"description": "vim - open/close folded text in vimdiff",
"tags": [
"vim",
"tools",
"keyboard",
"shortcuts",
"programming"
],
"contents": [
"# zo - to open folded text",
"# zc - to close folded text"
]
},
{
"id": 6,
"description": "jq - query to create new json with fields from another json",
"tags": [
"jq",
"tools",
"programming"
],
"contents": [
"$ jq '{(.foo) : .bar}' test.json # use the value of field \"foo\" as the key and value of \"bar\" as the value for new object",
"# () syntax is used to create a key for the resulting object",
"$ jq '{\"name\" : .name, \"age\": .age}' test.json # create new object with keys \"name\" and \"age\""
]
},
{
"id": 5,
"description": "go - split and join strings",
"tags": [
"golang",
"programming",
"shortcuts"
],
"contents": [
"// Use strings package to split and join strings",
"sentence := \"Minus eos autem rerum voluptas qui quisquam\"",
"words := strings.Split(sentence, \" \")",
"fmt.Println(strings.Join(words, \",\"))",
"// to split strings by whitespace",
"fmt.Println(strings.Fields(\"this is a space separated sentence\"))"
]
},
{
"id": 4,
"description": "vim - enable syntax foldmethod",
"tags": [
"vim",
"keyboard",
"shortcuts",
"programming"
],
"contents": [
"`:set foldmethod?` to show the current fold method // default is manual",
"`:set foldmethod=syntax` to quickly see an outline of the symbols and functions",
"`zx` - to open the current fold and close other folds",
"`zM` to close the all open folds",
"`zR` to open all the folds"
]
},
{
"id": 3,
"description": "vim - shortcut to access file path and directory",
"tags": [
"vim",
"keyboard",
"shortcuts",
"programming"
],
"contents": [
"`:Vexplore` to open the explorer at the directory of the current file in vertical window",
"`%` shorthand to get the current file name, path and extension.",
"`:echo expand('%')` - displays the relative path of the file. Apply modifiers on top of that get different fields",
"`echo expand('%:p')` - displays the absolute path of the file",
"`echo expand('%:t')` - displays just the name of the file",
"`echo expand('%:h')` - displays the directory name of the file",
"// This can also be applied in the shell commands executed from vim.",
"`!ls %:h` - runs `ls` command on the directory of the current file"
]
},
{
"id": 2,
"description": "vim - equally size windows",
"tags": [
"vim",
"keyboard",
"shortcuts"
],
"contents": [
"Ctrl+W = // to equally size the open windows"
]
},
{
"id": 1,
"description": "vim - open command history",
"tags": [
"vim",
"keyboard",
"shortcuts"
],
"contents": [
"q: // to open command history in editor just like :explore and :Vexplore"
]
}
]
Raw
techtips.json
[
{
"id": 94,
"description": "tmux - resize panes with keyboard shortcuts",
"tags": [
"tmux",
"keyboard",
"shortcuts",
"productivity"
],
"contents": [
"# To resize the current pane up/down/left/right",
"# Press prefix key followed by Modifier-key+Up/Down/Left/Right to resize in respective direction",
"# resizes by 5 rows/columns by default",
"# My prefix key is Ctrl+L (whereas Ctrl+B is the default). Modifier key is option key",
"# bindkey -r allows the key to be bound in repeat mode. So pressing twice M-Up after the prefix key (Ctrl+L) moves the pane up by 10 (2*5) rows",
"# bind-key -r M-Up resize-pane -U 5"
]
},
{
"id": 93,
"description": "vscode - insert multi line cursor in mac",
"tags": [
"vscode",
"keyboard",
"shortcuts"
],
"contents": [
"Cmd + Option + Up/Down - to insert cursor at the beginning of lines up or below",
"Option + Shift + I - to insert cursor at the end of the selected lines"
]
},
{
"id": 92,
"description": "gcp - cloud functions: manage functions with gcloud CLI",
"tags": [
"commands",
"gcp",
"cloud functions"
],
"contents": [
"# To list deployed functions",
"gcloud functions list",
"",
"# To deploy new functions or update an existing function",
"gcloud functions deploy",
"",
"# example: deploy a function with source code from local machine, python3.11 as runtime and pubsub topic as trigger",
"# To set up google cloud functions with environment variables specified in a yaml file, use `--env-vars-file` option",
"",
" gcloud functions deploy my-gcp-func \\",
" --gen2 \\",
" --region=us-central1 \\ # region to deploy",
" --runtime=python311 \\ # python 3.11 as the runtime",
" --source=. \\ # deploy with source code from current directory on the local machine",
" --entry-point=cloud_event_handler \\ # entry point function in main.py",
" --trigger-topic=pubsub-topic \\",
" --env-vars-file .env.yaml # file with list of environment variables to set up",
"",
"# Delete a cloud function",
"gcloud functions delete my-gcp-func",
"",
"# View logs from a cloud function",
"gcloud functions logs read my-gcp-func"
]
},
{
"id": 91,
"description": "gcp - pubsub: interact with pubsub through gcloud CLI",
"tags": [
"commands",
"gcp",
"pubsub"
],
"contents": [
"# To list subscribers of a topic",
"gcloud pubsub topics list-subscriptions my-pubsub-topic",
"",
"# To publish a message to pubsub topic",
"gcloud pubsub topics publish pubsub-topic1 --message \"hello,world\""
]
},
{
"id": 90,
"description": "Download compressed data and uncompress with CURL",
"tags": [
"linux",
"commands",
"curl"
],
"enabled": true,
"contents": [
"Add `--compressed` option to curl to auto decompress data after download.",
"e.g. curl --compressed https://api.stackexchange.com/2.2/sites"
]
},
{
"id": 89,
"description": "tempfile in Python",
"tags": [
"python",
"programming"
],
"enabled": true,
"contents": [
"Use tempfile.NamedTemporaryFile() callable to have a temporary file with a visible name",
"By default, file is opened in binary mode and is deleted on closing",
"Use \"w+\" to open in text mode.",
"Also works with context manager.",
">>> with tempfile.NamedTemporaryFile() as fp:",
"... fp.write(b'Hello world!')",
"... fp.seek(0)",
"... fp.read()",
"b'Hello world!'"
]
},
{
"id": 88,
"description": "Python: Get home directory",
"tags": [
"programming",
"python"
],
"enabled": true,
"contents": [
"Class method pathlib.Path.home() returns a new path object",
"representing user home directory (similar to os.path.expanduser(\"~\")",
"Path object also supports / operator, so Path.home()/subdir/file is also possible"
]
},
{
"id": 87,
"description": "Find which shell I am in",
"tags": [
"linux",
"shell"
],
"contents": [
"Run \"echo $SHELL\" ",
"root@88a325681e8c:/# echo $SHELL",
"/bin/bash"
]
},
{
"id": 86,
"description": "Find system information from command line",
"tags": [
"linux",
"shell"
],
"contents": [
"uname, uname -a",
"root@88a325681e8c:/# uname -a",
"Linux 88a325681e8c 4.9.184-linuxkit #1 SMP Tue Jul 2 22:58:16 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux",
""
]
},
{
"id": 85,
"description": "Find disk usage of directory and files with \"du\"",
"tags": [
"linux",
"shell",
"tools"
],
"contents": [
"du -a - display an entry for each file in the directory",
"du -c - display a grand total",
"du -h - display info in human readable form (take optional unit suffixes (-m for MB, -g for GB))",
"du -d <depth> - stop at given depth level"
]
},
{
"id": 84,
"description": "Access last executed command in shell",
"tags": [
"linux",
"shell"
],
"contents": [
"Use \"!!\" to access the last ran command"
]
},
{
"id": 83,
"description": "Get status of last command/process",
"tags": [
"linux",
"shell"
],
"contents": [
"$? - return the status of the last command ran in shell"
]
},
{
"id": 82,
"description": "Access arguments from last command",
"tags": [
"linux",
"programming",
"shell"
],
"contents": [
"!^ - First argument",
"!$ - Last argument",
"!* - All arguments"
]
},
{
"id": 81,
"description": "Colorize ls output",
"tags": [
"linux",
"shell"
],
"contents": [
"ls --color=always (on most Linux)",
"ls -G (on macOS)"
]
},
{
"id": 80,
"description": "List files with their disk usage",
"tags": [
"shell",
"linux"
],
"contents": [
"$ ls -lash",
"Shows a **long** listing of **all** files along with their ",
"**actual file size in number of blocks** (typically 512 bytes) and ",
"file size in **human readable** form (e.g B for bytes, K for kilobytes, G for gigabytes etc)"
]
},
{
"id": 79,
"description": "Supress newline character in shell",
"tags": [
"shell",
"linux"
],
"contents": [
"`echo -n` - skips the trailing newline character",
"Note: some shells do not support -n option.",
"For portability, use printf instead."
]
},
{
"id": 78,
"description": "Sort lines in shell",
"tags": [
"linux",
"shell"
],
"contents": [
"sort - command to sort lines of text or binary data from standard input or a file descriptor.",
"Default order: lexicographic",
"-k <column number> - sort by a specific key",
"-n - sort numerically",
"-s - keep the sorting order stable"
]
},
{
"id": 77,
"description": "Generate sequence of numbers",
"tags": [
"linux",
"shell"
],
"contents": [
"seq - Generate sequence of numbers",
"starts from 1 and increments 1 by default",
"$ seq 4 // generate 1 to 4",
"$ seq 10 2 20 // generate 10 to 20, increment by 2"
]
},
{
"id": 76,
"description": "Find system calls used by a program",
"tags": [
"linux",
"shell",
"programming"
],
"contents": [
"strace <program>"
]
},
{
"id": 75,
"description": "Find disk usage of files and directories",
"tags": [
"linux",
"shell"
],
"contents": [
"du - find disk usage of a directory and its files",
"-a - display an entry for each file in the directory",
"-c - display a grand total",
"-h - display info in human readable form (take optional unit suffixes: -m for MB, -g for GB)",
"-d <depth> - stop at given depth level"
]
},
{
"id": 74,
"description": "Where man pages are stored?",
"tags": [
"shell",
"linux"
],
"contents": [
"Pages are searched first in the path given by option `-M` if specified.",
"If `-M` is not specified, then the path specified in `MANPATH` is looked up.",
"If neither `-M` nor `MANPATH` is specified, then the path to man pages is inferred from the config file.",
"In general, the default set of man pages live in `/usr/share/man/`",
"Applications can install in other paths too and update the `MANPATH` accordingly.",
"The location of the config file can differ based on the distribution.",
"/private/etc/man.conf - in macOS Mojave",
"/etc/man.config - in many linux distributions"
]
},
{
"id": 73,
"description": "Convert epoch seconds into date",
"tags": [
"linux",
"commands",
"shell",
"datetime"
],
"contents": [
"% date -r <seconds> # macOS",
"$ date -d @<seconds> # on most linux",
"$ date +%s # display current time in epoch seconds"
]
},
{
"id": 72,
"description": "Toggle reader mode in Safari",
"tags": [
"macOS",
"shortcuts",
"safari"
],
"contents": [
"`Cmd + Shift + R` - toggles reader mode on supported sites"
]
},
{
"id": 71,
"description": "Find files modified in last x minutes or x days",
"tags": [
"shell",
"find",
"linux",
"commands"
],
"contents": [
"`$ find . -mmin -60` - find files modified in the last 60 minutes in current directory",
"`$ find . -mtime -2` - find files modified in the last 48 hours in current directory"
]
},
{
"id": 70,
"description": "Find files accessed in last x minutes or x days",
"tags": [
"shell",
"find",
"linux",
"commands"
],
"contents": [
"`$ find . -amin -60` - find files modified in the last 60 minutes in current directory",
"`$ find . -atime -2` - find files modified in the last 48 hours in current directory"
]
},
{
"id": 69,
"description": "sshpass - specify password for ssh/scp login non-interactively",
"tags": [
"shell",
"linux",
"commands",
"scp"
],
"contents": [
"`sshpass -p <password> ssh user@host \"command to run\"` - Use the specified password to connect using ssh",
"`sshpass -p <password> scp <source> <destination>` - Use the specified password to connect using scp",
"`SSHPASS=password sshpass -e ssh user@host command` - Take the password from the environment variable SSHPASS"
]
},
{
"id": 68,
"description": "scp - some helpful options (pqr)",
"tags": [
"shell",
"linux",
"commands",
"scp"
],
"contents": [
"`-p` - Preserve modification times, access times, and modes",
"`-q` - Quiet mode: disables the progress meter as well as warning and diagnostic messages from ssh",
"`-r` - Recursively copy entire directories"
]
},
{
"id": 67,
"description": "ssh options - Ignore host key checking",
"tags": [
"ssh",
"shell",
"commands",
"options"
],
"contents": [
"`-o StrictHostKeyChecking=no` - automatically add new host keys to users known hosts file. Often not needed in controlled environments",
"`-o UserKnownHostsFile=/dev/null` - Use /dev/null instead of the default file (~/.ssh/known_hosts)",
"Set `StrictHostKeyChecking no` in .ssh/config under `Host <hostname>` to apply this to per hosts"
]
},
{
"id": 66,
"description": "bash - a quick note on arrays",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"arr=() # Create empty array",
"arr+=(5) # Append a number to array",
"arr+=(xyz) # Append a text to array; arrays can have numbers and strings",
"${arr[@]} # Get all items from the array",
"${!arr[@]} # Get all indices of the array. Index starts at 0",
"${arr[3]} # Get the fourth item from the array",
"${arr} # Get first item from the array. Equivalent to ${arr[0]}",
"${arr[@]:i:n} # Get n elements starting at index i",
"arr=( $(cmd) ) # Save output of a command into an array",
"# Sample for loop",
"for item in ${arr[@]};do",
" echo $item",
"done"
]
},
{
"id": 65,
"description": "vim - show relative and absolute file path",
"tags": [
"vim",
"programming",
"editor",
"shortcuts"
],
"contents": [
"Ctrl+G - shows the relative path of the current file",
"{n}Ctrl+G - shows the relative path of the nth file in the buffer",
"1Ctrl+G - shows the absolute path of the current file"
]
},
{
"id": 64,
"description": "vim - set/toggle option",
"tags": [
"vim",
"shortcuts",
"editor",
"programming"
],
"contents": [
":set <option> - switches on a toggle option",
":set <option>! - toggles the option",
":set <option>? - shows the value of option",
"e.g :set nu - turns on the line number, :set nonumber - turns off the line number",
":set nu! toggles the line number on or off,"
]
},
{
"id": 63,
"description": "bash: read inputs",
"tags": [
"bash",
"programming",
"shell"
],
"contents": [
"read var # gets the input from the user and assings to the variable \"var\"",
"read -p \"Prompt\" var # shows the prompt message",
"read -ps \"Prompt\" var # shows the prompt message, but keeps the input hidden.",
"# E.g.",
"# $ read -p \"Select: \" choice",
"# Select: 1",
"# $ echo $choice",
"# 1"
]
},
{
"id": 62,
"description": "vscode: terminal shortcuts",
"tags": [
"vscode",
"shortcuts",
"terminal",
"productivity"
],
"contents": [
"`Cmd + \\` - keyboard shortcut to split the terminal vertically",
"`Cmd + Option + Left` - focus to the window on the left",
"`Cmd + Option + Right` - focus to the window on the right",
"`Cmd + j` - hide the terminal window and focus on active editor group"
]
},
{
"id": 61,
"description": "bash: arithmetic with let",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"let # evaluates each argument as an arithmetic expression",
"let a=1+9 # assigns a=10",
"# If spacing needed for better readability, enclose the expression between quotes",
"let \"b = 2 + 8\" # assigns b=10",
"# Take values from variables",
"let c=$a+$b # assigns sum of a and b to c",
"# No escaping needed for *",
"let \"d = $a * $b\" # assigns product of a and b to d",
"let d++ # increment d by 1 and assign to d"
]
},
{
"id": 60,
"description": "bash: arithmetic with expr",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"expr 2 + 7 # evaluate the expression and writes to standard output. Spaces are needed between the tokens",
"# multiplication operator * need to be escaped",
"expr 7 * 3 # results in syntax error",
"expr 7 \\* 3 # evaluates to 21",
"e=$(expr 2 + 7) # evaluate the expression and assign. Similar to $((expression))",
"expr 2+7 # prints the expression as is without evaluating",
"expr \"2 + 7\" # prints the expression as is without evaluating even with quotes"
]
},
{
"id": 59,
"description": "bash: arithmetic expansion",
"tags": [
"bash",
"shell",
"programming"
],
"contents": [
"# $((expression)) - evaluates the expression and substitutes the result.",
"echo $((3+5)) # prints 8",
"# spaces are totally fine",
"f=$((4 + 4)) # evaluate the expression and assign the value to a variable",
"g=$((f * 2)) # variables inside the expression need not be specified with a preceding $ sign",
"echo $((g--)) $((g++)) # increment, decrement",
"echo ((g += 5) # assignment operators (= *= /= %= += -= <<= >>= &= ^= |=) are also supported"
]
},
{
"id": 58,
"description": "ffmpeg2 - Convert video to gif",
"tags": [
"tools",
"ffmpeg"
],
"contents": [
"# Supports multiple input file formats",
"# -r <frame rate>",
"# -vf <filter_graph> # e.g. -vf scale=w:hP",
"ffmpeg2 -i <input file> -r 10 output.gif",
"# set width to 320px and set height based on the width keeping the aspect ratio",
"ffmpeg2 -i <input file> -r 10 -vf scale=320:-1 output.gif"
]
},
{
"id": 57,
"description": "bash: print values in hex",
"tags": [
"bash"
],
"contents": [
"printf \"0x%x\\n\", 369098752 # prints the value in hex format. e.g. 0x16000000"
]
},
{
"id": 56,
"description": "vim: yank shortcuts",
"tags": [
"vim",
"shortcuts"
],
"contents": [
"`yw` - copy from current to start of the next word",
"`yb` - copy from current to beginning of the current word",
"`y$` - copy till the end of the line",
"`y0` - copy till the start of the line",
"`{n}Y` - copy n number of lines",
"`{n}yy` - copy n number of lines"
]
},
{
"id": 55,
"description": "C: Get system time in epoch seconds (number of seconds since 1970-01-01 00:00:00 +0000 (UTC))",
"tags": [
"c",
"programming",
"datetime"
],
"contents": [
"time_t curtime = time(NULL); // time() included from time.h",
"(void)time(&curtime); // also sets the seconds in the input buffer if given",
"// can also get the time in microsecond granularity with gettimeofday",
"struct timeval tm;",
"struct timezone tz",
"(void)gettimeofday(&tm, &tz); // included from sys/time.h",
"// tm.tv_sec - epoch time in seconds",
"// tm.tv_usec - microseconds",
"// tz.tz_dsttime - is Daylight Savings on?",
"// tz.tz_minuteswest - number of minutes from the GMT",
"printf(\"secs=%lu, msecs=%d, is_dst=%d, minutes_from_gmt=%d\n\", tm.tv_sec, tm.tv_usec, tz.tz_dsttime, tz.tz_minuteswest);",
"printf(\"timestamp=%s\", ctime(&tm.tv_sec)); // get clock time as a readable string",
"// ctime returns a pointer to statically allocated buffer holding the stamp.",
"// Subsequent calls to ctime() would overwrite the buffer. Use ctime_r() to write the string to user provided buffer instead."
]
},
{
"id": 54,
"description": "bash: display information about a command type",
"tags": [
"shell",
"bash",
"programming"
],
"contents": [
"type arg # arg can be a command, function, aliases an built-ins",
"type -a arg # display all locations containing an executable named NAME",
"type -t arg # output a single word which is one of alias, keyword, function, builtin, file",
"# e.g.",
"ubuntu@ubuntu-lts:~$ os_release()",
"> {",
"> cat /etc/os-release",
"> }",
"ubuntu@ubuntu-lts:~$ type -t os_release",
"function",
"ubuntu@ubuntu-lts:~$ type -a os_release",
"os_release is a function",
"os_release ()",
"{",
" cat /etc/os-release",
"}"
]
},
{
"id": 53,
"description": "regex: filter ipv4 address",
"tags": [
"linux",
"tools",
"regex"
],
"contents": [
"# regex pattern to filter IPv4 addresses",
"# upto 3 digits followed by ., repeated 3 times and up to 3 digits",
"# this is too generic. so invalid IPs like 333.232.444.999 would also be considered valid",
"ifconfig | egrep -o '([0-9]{1,3}\\.){3}[0-9]{1,3}'",
"# To search for only valid IP addr and output only the IP addr",
"ifconfig | egrep -o '((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)'",
"# Skip localhost and subnet masks",
"ifconfig | egrep -o '((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)' | egrep -v '^255|127.0.0.1'"
]
},
{
"id": 52,
"description": "sed - Get a line or range of lines",
"tags": [
"linux",
"tools",
"shell",
"sed"
],
"contents": [
"# Get contents of line number n from file",
"# -n - tells sed not to print the lines unless explicity requested",
"# 'p' - print command",
"# 'q' - quit sed",
"sed -n '10p' # print line number 10, but will continue processing the rest of the file too",
"sed -n '10p;11q' # print line number 10 and quit processing",
"sed -n '5,10p;11q' # print line number from 5 to 10 and quit processing"
]
},
{
"id": 51,
"description": "grep - find empty lines",
"tags": [
"linux",
"shell",
"tools",
"grep"
],
"contents": [
"grep -n '^$' <file> # print line numbers of empty lines in the given file"
]
},
{
"id": 50,
"description": "vim - clear all trailing whitespaces",
"tags": [
"linux",
"vim",
"tools"
],
"contents": [
"\" function to clear trailing white spaces",
"fun! TrimTrailingWhiteSpace()",
" let l:save = winsaveview()",
" keeppatterns %s/\\s\\+$//e",
" call winrestview(l:save)",
" \" without saving and restoring the view, the cursor",
" \" moves to the line of the last search result where",
" \" the edit is made",
"endfun",
"",
"\" Use a shortcut to invoke the function",
"\" for e.g. I use the leader key \\ followed by w",
"\\ + w to clear the trailing whitespace",
":noremap <Leader>w :call TrimTrailingWhiteSpace()<CR>"
]
},
{
"id": 49,
"description": "openssl - show certificate validity",
"tags": [
"tools",
"openssl"
],
"contents": [
"# show notBefore and notAfter date of the given certificate",
"openssl x509 -noout -startdate -enddate -in <certificate>",
"# print all details of the certificate in text format",
"openssl x509 -noout -text -in root_ca.crt"
]
},
{
"id": 48,
"description": "Python: Get host name of the system",
"tags": [
"python",
"scripts"
],
"contents": [
"import socket",
"print(socket.gethostname()) # print hostname to stdout"
]
},
{
"id": 47,
"description": "Python: Get interpreter history",
"tags": [
"python",
"programming"
],
"contents": [
"# History of commands run in python interpreter are cached at $HOME/.python_history",
"# readline module provides the methods to access the entries from the underlying history buffer",
"# readline.get_current_history_length() returns the current number of items",
"# readline.get_history_item(index) returns the item at the given index",
"import readline",
"history_length = readline.get_current_history_length()",
"for i in range(1, history_length):",
" print(readline.get_history_item(i)"
]
},
{
"id": 46,
"description": "Python: Startup scripts for the interactive sessions",
"tags": [
"programming",
"python"
],
"contents": [
"# If the environment variable PYTHONPATH points to a readable file",
"# commands in that file are executed before the prompt is given to the",
"# user in interactive mode",
"# e.g. export PYTHONPATH=$HOME/.pythonrc.py"
]
},
{
"id": 45,
"description": "vim - switching between vim buffers",
"tags": [
"programming",
"productivity",
"vim",
"editor"
],
"contents": [
":buffers or :ls or :files - list open buffers",
":bn, :bnext - go to next buffer",
":bp, :bprev - go to previous buffer",
":b <filename> - go to buffer with the given file name",
":b ex - open buffer with filename starting with ex",
"Ctrl-6 - toggle between current and last buffer"
]
},
{
"id": 44,
"description": "vim - search patterns using vimgrep",
"tags": [
"vim",
"productivity",
"editor",
"programming"
],
"contents": [
":vimgrep /{pattern}/[g][j] {filenames} - search pattern in given files and update quicklist (aka error list)",
" - {pattern} follows vim regex pattern",
" - g - return all matches",
" - j - update quick list only. do not jump to the first match.",
" vimgrep loads the file into memory, so can be slow for large files",
":cn - go to next match in the quick list",
":cp - go to previous match in the quick list",
":cc n - go to nth match in the quick list",
":clist [from] [to] - list all errors that are valid",
":copen - open a window to show list of errors"
]
},
{
"id": 43,
"description": "vim - misc shortcuts",
"tags": [
"vim",
"editor",
"productivity"
],
"contents": [
"q: - (in command mode) to list the commands in chronological order. Allows editing too",
":history - list commands from history table",
":set <setting-name>? - show the current value of the given setting",
":echo &<setting-name> - show the current value of the given setting",
":echo &cmdwinheight - show the current value of cmdwinheight",
":set! all - show all settings, one per line",
":set cmdwinheight=10 - set the height of the command history window to 10. Default is 7"
]
},
{
"id": 42,
"description": "git - revert changes to a single file",
"tags": [
"git",
"shortcuts"
],
"contents": [
"git checkout [commit ID] -- /path/to/your/file # Defaults to HEAD if no commit ID is specified"
]
},
{
"id": 41,
"description": "Python - register functions to be called at exit",
"tags": [
"python",
"programming"
],
"contents": [
"import atexit",
"atexit.register(func1) # register func1 to be called when interpreter exits (some exceptions apply)",
"atexit.register(func2, arg1, arg2) # func2(arg1, arg2) will be called at exit",
"atexit.register(func3, arg1=\"foo\", arg2=\"bar\") # func3(arg1=\"foo\", arg2=\"bar\") will be called at exit",
"@atexit.register # use decorator to register functions. Can't be used with functions with args",
"def func4():",
" print(\"Bye\")",
"# registered functions are called in last-in-first-out order"
]
},
{
"id": 40,
"description": "Makefile - automatic variables within the recipe",
"tags": [
"programming",
"makefile"
],
"contents": [
"# $@ - file name of the target of the rule",
"# $< - name of the first prerequisite",
"# $? - names of all prerequisites that newer than target",
"# $^ - name of all prerequisites",
"# NOTE: these variables are available only within the recipe of a target"
]
},
{
"id": 39,
"description": "Python: pretty print python data structures",
"tags": [
"python",
"programming"
],
"contents": [
"# pprint module provides a way to pretty print arbitrary",
"# data structures including the built in data types.",
"import pprint",
"pprint.print(mydict)",
"# pprint.print defaults to 80 columns per line.",
"# depth and indent level can be adjusted too"
]
},
{
"id": 38,
"description": "shell - delimit by consecutive whitespaces/tabs in cut",
"tags": [
"programming",
"shell"
],
"contents": [
"# -w option to cut filters the text using whitespaces and tabs as delimiters",
"# consecutive white spaces and tabs counted as single field",
"cut -w -f 4-6 # filter the lines by whitespaces/tab and output fields 4 through 6",
"# NOTE: This is available only in cut implementation conforming to (\u201cPOSIX.2\u201d)",
"# supported on macOS"
]
},
{
"id": 37,
"description": "macOS - show emoji keyboard",
"tags": [
"macOS",
"keyboard",
"shortcuts"
],
"contents": [
"Ctrl + Cmd + Spacebar -> to bring up emoji keyboard \ud83d\ude0e"
]
},
{
"id": 36,
"description": "ssh - disable login banner",
"tags": [
"linux",
"ssh",
"productivity"
],
"contents": [
"# create /home/$USER/.hushlogin to suppress ssh login banner for a particular user"
]
},
{
"id": 35,
"description": "golang - discard all writes",
"tags": [
"programming",
"golang"
],
"contents": [
"io.Discard is equivalent /dev/null",
"All writes to io.Discard succeeds without doing anything"
]
},
{
"id": 34,
"description": "shell - get specific line in a file",
"tags": [
"programming",
"shell"
],
"contents": [
"# there are multiple ways to do this. I find sed easier than others",
"# sed -n 'np' file - to get nth line a file",
"sed -n '10p' file # to get 10th line in a file"
]
},
{
"id": 33,
"description": "shell - set the positional parameters",
"tags": [
"programming",
"shell"
],
"contents": [
"# Set the values of the positional parameters to script, bash functions",
"# set foo to $1, bar to $2",
"set -- foo bar"
]
},
{
"id": 32,
"description": "jq - filter keys with special characters",
"tags": [
"json",
"programming",
"tools",
"jq"
],
"contents": [
"# If keys in json data contain special characters, the keys need to be enclosed in \"\" in the jq filter string",
"# e.g. ",
"kubectl get secrets cluster-xyz -o json | jq -r '.data.\"tls.crt\"' | base64 --decode"
]
},
{
"id": 31,
"description": "tmux - send commands to multiple panes at the same time",
"tags": [
"tmux",
"programming",
"tools",
"shortcuts"
],
"contents": [
"Prefix key + : - to bring command prompt",
":setw synchronize-panes on - to turn on command synchronization",
":setw synchronize-panes off - to turn off command synchronization",
"The default prefix is Ctrl-B. I use Ctrl-L"
]
},
{
"id": 30,
"description": "du - display the size of directories, skip subdirectories",
"tags": [
"linux",
"shell",
"commands",
"tools"
],
"contents": [
"# du displays the size of the subdirectories as well by default.",
"du -sch dir1 dir2 #display size of dir1 and dir2 and the grand total in human readable form"
]
},
{
"id": 29,
"description": "macOS/finder - keyboard shortcuts",
"tags": [
"macOS",
"keyboard",
"shortcuts"
],
"contents": [
"Cmd + Shift + N - to create a new folder",
"Cmd + Delete - to delete a file or folder"
]
},
{
"id": 28,
"description": "gdb - dump backtrace of all threads",
"tags": [
"programming",
"gdb",
"debugging"
],
"contents": [
"#dump backtrace of all threads",
"thread apply all backtrace"
]
},
{
"id": 27,
"description": "git - undo uncommited local changes to a specific file",
"tags": [
"programming",
"git"
],
"contents": [
"# To undo uncommitted local changes to a specific file.",
"# This command overwrites the current version of filename",
" with the version from remote branch",
"<filename> is specified as per path spec. See https://git-scm.com/docs/gitglossary#Documentation/gitglossary.txt-aiddefpathspecapathspec",
"# git checkout -- filename"
]
},
{
"id": 26,
"description": "git - add a remote branch and set local branch to push to new remote branch",
"tags": [
"programming",
"git"
],
"contents": [
"# The workflow goes like this",
"# git checkout -b <a_new_branch>",
"# make edits..make commits..time to push to remote branch and/or create PR",
"# git push --set-upstream origin <a_new_branch>",
"# git push"
]
},
{
"id": 25,
"description": "git - deleting a branch",
"tags": [
"programming",
"git"
],
"contents": [
"git branch -d <branch> # to delete local branch",
"git branch -D <branch> # to force delete local branch",
"git push <remote> --delete <remote-branch-name> # to delete remote branch.",
"# e.g. git push origin --delete pr123456"
]
},
{
"id": 24,
"description": "vim - open multiple files in tabs",
"tags": [
"programming",
"vim",
"editor",
"productivity"
],
"contents": [
"# use option -p with vim to open multiple files in tabs",
"vim -p file1 file2 file3"
]
},
{
"id": 23,
"description": "docker - display only repo and tag info in docker images",
"tags": [
"docker",
"commands",
"tools"
],
"contents": [
"# to display only image repo and tag information in 'docker images' command",
"# useful when including the output in other commands such as docker run",
"docker images --format '{{.Repository}}:{{.Tag}}'"
]
},
{
"id": 22,
"description": "markdown - insert multi line quote",
"tags": [
"markdown",
"editor"
],
"contents": [
"`>` - inserts a block quote in markdown.",
"Add two spaces at the end of line to make a multi line quote",
"> Stay hungry",
"> Stay foolish",
"will produce | Stay hungry Stay foolish",
"> Stay hungry ",
"> Stay foolish ",
"will produce",
"| Stay hungry",
"| Stay foolish"
]
},
{
"id": 21,
"description": "valgrind - check mem leaks, double free, double free",
"tags": [
"c",
"programming",
"tools",
"valgrind"
],
"contents": [
"valgrind --tool=memcheck --leak-check=yes --track-origins=yes <executable>"
]
},
{
"id": 20,
"description": "tmux - reclaim the entire window during attach",
"tags": [
"tmux",
"terminal",
"productivity"
],
"contents": [
"# After attaching to a session, tmux can sometimes fill the window with L-shaped ",
"# ....., leaving very little space for the actual client. This can happen if the ",
"# session is attached elsewhere. Use the flag -d to detach the existing session.",
"$ tmux attach-session -d"
]
},
{
"id": 19,
"description": "Python - Get current time with timezone info",
"tags": [
"python",
"programming",
"datetime"
],
"contents": [
"# Use pytz.timezone to add timezone info when dealing with datetime",
">>> from datetime import datetime",
">>> from pytz import timezone",
">>> now = datetime.now(tz=timezone(\"EST\"))",
">>> now",
"datetime.datetime(2022, 11, 11, 12, 6, 3, 779069, tzinfo=<StaticTzInfo 'EST'>)",
">>> # another way to do the same",
"... ",
">>> eastern = timezone(\"US/Eastern\")",
">>> now = eastern.localize(datetime.now())",
">>> now.tzinfo",
"<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>"
]
},
{
"id": 18,
"description": "Python - using pathlib for quick actions with files",
"tags": [
"python",
"programming",
"io"
],
"contents": [
"# for simple actions like opening a file and just reading some text",
"# or writing few lines of text in a string, pathlib.Path can be a great option",
"# it abstracts away the usual workflow of opening a file, writing and closing",
"# into convenient functions",
">>> from pathlib import Path",
">>> myfile = Path(\"foobar.txt\")",
">>> myfile.write_text(\"foobar\")",
"6",
">>> myfile.read_text()",
"'foobar'"
]
},
{
"id": 17,
"description": "shell - list only directories",
"tags": [
"shell",
"commands",
"shortcuts",
"linux"
],
"contents": [
"# ls */ - lists directories recursively",
"# ls -d */ - lists only directories in current directory",
"ls -d */",
"# another way to do this, but in long listing format",
"# ls -l | grep ^d"
]
},
{
"id": 16,
"description": "tools - list contents of a tar/tar.gz archive",
"tags": [
"shell",
"tools",
"productivity",
"shortcuts"
],
"contents": [
"# to simply list contents of a tar archive without unarchiving it",
"tar -tvf file.tar # list conents of .tar file",
"tar -tzvf file.tar.gz # list contents of zipped tar",
"tar -jtvf file.tar.bz2 # list contents of tar.bz2 file",
"tar -tvf file.tar '*.cpp' # search for .cpp files in the archive"
]
},
{
"id": 15,
"description": "Python - read contents pointed by a URL",
"tags": [
"python",
"programming"
],
"contents": [
"# read contents of a link using requests",
"r = requests.get(\"https://someurl.com/somefile.json\")",
"# gets a response object",
"r.text # to read the contents as a text",
"r.json() # to return a json dict of the data pointed by the url"
]
},
{
"id": 14,
"description": "Python - validate a string is valid URL or not",
"tags": [
"python",
"programming",
"productivity"
],
"contents": [
"# using validators package",
"import validators",
"# validators.url() returns true if the url is valid",
"is_url = validators.url(\"https://someurl.com\")"
]
},
{
"id": 13,
"description": "Python - process shell command result line by line",
"tags": [
"python",
"programming",
"shell",
"snippets"
],
"contents": [
">>> import subprocess",
">>> cmd_result = subprocess.run(\"ls -l\".split(), text=True, capture_output=True)",
">>> # split the output by newline to process each line",
">>> for line in cmd_result.stdout.split(\"\n\"):",
"... if line.startswith('d'):",
"... # processing only directories",
"... print(line)",
"...",
"drwxr-xr-x 1 root root 4096 Nov 9 08:42 man1",
"drwxr-xr-x 2 root root 4096 Nov 9 08:42 man5",
"drwxr-xr-x 2 root root 4096 Nov 9 08:07 man8"
]
},
{
"id": 12,
"description": "shell - get absolute path of a link",
"tags": [
"bash",
"shell",
"shortcuts",
"programming"
],
"contents": [
"$ readlink -f path-to-link # recursively resolve and return the canononical path of the link"
]
},
{
"id": 11,
"description": "vscode - cmd shortcut to jump to bracket",
"tags": [
"vscode",
"keyboard",
"shortcuts"
],
"contents": [
"\"Cmd + Shift + \\\" to go to the end / beginning of a code block",
"If the middle of a block, it jumps to the end of the block."
]
},
{
"id": 10,
"description": "C - Generate random int",
"tags": [
"c",
"cpp",
"snippets"
],
"contents": [
"// Generate random ints with rand() in the range of 0 to RAND_MAX (defined in stdlib.h)",
"// RAND_MAX is set to 2147483647 in case of mac",
"printf(\"a random number:%d\", rand());",
"// Seed with srand(unsigned seed_value), often the seed_value is the current timestamp",
"srand(time(NULL));",
"printf(\"another random number:%d\", rand());"
]
},
{
"id": 9,
"description": "shell - sum numbers from stdin",
"tags": [
"shell",
"commands",
"tools"
],
"contents": [
"# Ways to sum up numbers from stdin or from piped output from previous commands",
"# Using paste command",
"$ echo somefile | paste -s -d+ | bc",
"$ cat nums | paste -sd+ - | bc",
"# using awk.. substitute $1 with the actual column number",
"$ cat nums | awk '{sum += $1} END {print sum}'"
]
},
{
"id": 8,
"description": "cpp - google style guide - typenames, filenames, variables",
"tags": [
"cpp",
"programming",
"code"
],
"contents": [
"# filenames - all lower case and can include `-` or `_`. e.g. my_class.h my_class.cc",
"# typenames - in PascalCase - applies to classes, structs, type alias, enums and type templates",
"# variables - all lower case, words separated by `_`. local variables, function parameters, class members"
]
},
{
"id": 7,
"description": "vim - open/close folded text in vimdiff",
"tags": [
"vim",
"tools",
"keyboard",
"shortcuts",
"programming"
],
"contents": [
"# zo - to open folded text",
"# zc - to close folded text"
]
},
{
"id": 6,
"description": "jq - query to create new json with fields from another json",
"tags": [
"jq",
"tools",
"programming"
],
"contents": [
"$ jq '{(.foo) : .bar}' test.json # use the value of field \"foo\" as the key and value of \"bar\" as the value for new object",
"# () syntax is used to create a key for the resulting object",
"$ jq '{\"name\" : .name, \"age\": .age}' test.json # create new object with keys \"name\" and \"age\""
]
},
{
"id": 5,
"description": "go - split and join strings",
"tags": [
"golang",
"programming",
"shortcuts"
],
"contents": [
"// Use strings package to split and join strings",
"sentence := \"Minus eos autem rerum voluptas qui quisquam\"",
"words := strings.Split(sentence, \" \")",
"fmt.Println(strings.Join(words, \",\"))",
"// to split strings by whitespace",
"fmt.Println(strings.Fields(\"this is a space separated sentence\"))"
]
},
{
"id": 4,
"description": "vim - enable syntax foldmethod",
"tags": [
"vim",
"keyboard",
"shortcuts",
"programming"
],
"contents": [
"`:set foldmethod?` to show the current fold method // default is manual",
"`:set foldmethod=syntax` to quickly see an outline of the symbols and functions",
"`zx` - to open the current fold and close other folds",
"`zM` to close the all open folds",
"`zR` to open all the folds"
]
},
{
"id": 3,
"description": "vim - shortcut to access file path and directory",
"tags": [
"vim",
"keyboard",
"shortcuts",
"programming"
],
"contents": [
"`:Vexplore` to open the explorer at the directory of the current file in vertical window",
"`%` shorthand to get the current file name, path and extension.",
"`:echo expand('%')` - displays the relative path of the file. Apply modifiers on top of that get different fields",
"`echo expand('%:p')` - displays the absolute path of the file",
"`echo expand('%:t')` - displays just the name of the file",
"`echo expand('%:h')` - displays the directory name of the file",
"// This can also be applied in the shell commands executed from vim.",
"`!ls %:h` - runs `ls` command on the directory of the current file"
]
},
{
"id": 2,
"description": "vim - equally size windows",
"tags": [
"vim",
"keyboard",
"shortcuts"
],
"contents": [
"Ctrl+W = // to equally size the open windows"
]
},
{
"id": 1,
"description": "vim - open command history",
"tags": [
"vim",
"keyboard",
"shortcuts"
],
"contents": [
"q: // to open command history in editor just like :explore and :Vexplore"
]
}
]
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