Command Line Tips and Tricks

bash-tips.sh

#!/bin/bash
##############################################################################
# SHORTCUTS
##############################################################################


CTRL+A  # move to beginning of line
CTRL+B  # moves backward one character
CTRL+C  # halts the current command
CTRL+D  # deletes one character backward or logs out of current session, similar to exit
CTRL+E  # moves to end of line
CTRL+F  # moves forward one character
CTRL+G  # aborts the current editing command and ring the terminal bell
CTRL+J  # same as RETURN
CTRL+K  # deletes (kill) forward to end of line
CTRL+L  # clears screen and redisplay the line
CTRL+M  # same as RETURN
CTRL+N  # next line in command history
CTRL+O  # same as RETURN, then displays next line in history file
CTRL+P  # previous line in command history
CTRL+R  # searches backward
CTRL+S  # searches forward
CTRL+T  # transposes two characters
CTRL+U  # kills backward from point to the beginning of line
CTRL+V  # makes the next character typed verbatim
CTRL+W  # kills the word behind the cursor
CTRL+X  # lists the possible filename completions of the current word
CTRL+Y  # retrieves (yank) last item killed
CTRL+Z  # stops the current command, resume with fg in the foreground or bg in the background

ALT+B   # moves backward one word
ALT+D   # deletes next word
ALT+F   # moves forward one word

DELETE  # deletes one character backward
!!      # repeats the last command
exit    # logs out of current session


##############################################################################
# BASH BASICS
##############################################################################

env                 # displays all environment variables

echo $SHELL         # displays the shell you're using
echo $BASH_VERSION  # displays bash version

bash                # if you want to use bash (type exit to go back to your previously opened shell)
whereis bash        # finds out where bash is on your system
which bash          # finds out which program is executed as 'bash' (default: /bin/bash, can change across environments)

clear               # clears content on window (hide displayed lines)


##############################################################################
# FILE COMMANDS
##############################################################################


ls                            # lists your files in current directory, ls <dir> to print files in a specific directory
ls -l                         # lists your files in 'long format', which contains the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified
ls -a                         # lists all files, including hidden files (name beginning with '.')
ln -s <filename> <link>       # creates symbolic link to file
touch <filename>              # creates or updates (edit) your file
cat <filename>                # prints file raw content (will not be interpreted)
any_command > <filename>      # '>' is used to perform redirections, it will set any_command's stdout to file instead of "real stdout" (generally /dev/stdout)
more <filename>               # shows the first part of a file (move with space and type q to quit)
head <filename>               # outputs the first lines of file (default: 10 lines)
tail <filename>               # outputs the last lines of file (useful with -f option) (default: 10 lines)
vim <filename>                # opens a file in VIM (VI iMproved) text editor, will create it if it doesn't exist
mv <filename1> <dest>         # moves a file to destination, behavior will change based on 'dest' type (dir: file is placed into dir; file: file will replace dest (tip: useful for renaming))
cp <filename1> <dest>         # copies a file
rm <filename>                 # removes a file
diff <filename1> <filename2>  # compares files, and shows where they differ
wc <filename>                 # tells you how many lines, words and characters there are in a file. Use -lwc (lines, word, character) to ouput only 1 of those informations
chmod -options <filename>     # lets you change the read, write, and execute permissions on your files (more infos: SUID, GUID)
gzip <filename>               # compresses files using gzip algorithm
gunzip <filename>             # uncompresses files compressed by gzip
gzcat <filename>              # lets you look at gzipped file without actually having to gunzip it
lpr <filename>                # prints the file
lpq                           # checks out the printer queue
lprm <jobnumber>              # removes something from the printer queue
genscript                     # converts plain text files into postscript for printing and gives you some options for formatting
dvips <filename>              # prints .dvi files (i.e. files produced by LaTeX)
grep <pattern> <filenames>    # looks for the string in the files
grep -r <pattern> <dir>       # search recursively for pattern in directory


##############################################################################
# DIRECTORY COMMANDS
##############################################################################


mkdir <dirname>  # makes a new directory
cd               # changes to home
cd <dirname>     # changes directory
pwd              # tells you where you currently are


##############################################################################
# SSH, SYSTEM INFO & NETWORK COMMANDS
##############################################################################


ssh user@host            # connects to host as user
ssh -p <port> user@host  # connects to host on specified port as user
ssh-copy-id user@host    # adds your ssh key to host for user to enable a keyed or passwordless login

whoami                   # returns your username
passwd                   # lets you change your password
quota -v                 # shows what your disk quota is
date                     # shows the current date and time
cal                      # shows the month's calendar
uptime                   # shows current uptime
w                        # displays whois online
finger <user>            # displays information about user
uname -a                 # shows kernel information
man <command>            # shows the manual for specified command
df                       # shows disk usage
du <filename>            # shows the disk usage of the files and directories in filename (du -s give only a total)
last <yourUsername>      # lists your last logins
ps -u yourusername       # lists your processes
kill <PID>               # kills the processes with the ID you gave
killall <processname>    # kill all processes with the name
top                      # displays your currently active processes
bg                       # lists stopped or background jobs ; resume a stopped job in the background
fg                       # brings the most recent job in the foreground
fg <job>                 # brings job to the foreground

ping <host>              # pings host and outputs results
whois <domain>           # gets whois information for domain
dig <domain>             # gets DNS information for domain
dig -x <host>            # reverses lookup host
wget <file>              # downloads file


##############################################################################
# VARIABLES
##############################################################################


varname=value                # defines a variable
varname=value command        # defines a variable to be in the environment of a particular subprocess
echo $varname                # checks a variable's value
echo $$                      # prints process ID of the current shell
echo $!                      # prints process ID of the most recently invoked background job
echo $?                      # displays the exit status of the last command
export VARNAME=value         # defines an environment variable (will be available in subprocesses)

array[0]=valA                # how to define an array
array[1]=valB
array[2]=valC
array=([2]=valC [0]=valA [1]=valB)  # another way
array=(valA valB valC)              # and another

${array[i]}                  # displays array's value for this index. If no index is supplied, array element 0 is assumed
${#array[i]}                 # to find out the length of any element in the array
${#array[@]}                 # to find out how many values there are in the array

declare -a                   # the variables are treaded as arrays
declare -f                   # uses function names only
declare -F                   # displays function names without definitions
declare -i                   # the variables are treaded as integers
declare -r                   # makes the variables read-only
declare -x                   # marks the variables for export via the environment

${varname:-word}             # if varname exists and isn't null, return its value; otherwise return word
${varname:=word}             # if varname exists and isn't null, return its value; otherwise set it word and then return its value
${varname:?message}          # if varname exists and isn't null, return its value; otherwise print varname, followed by message and abort the current command or script
${varname:+word}             # if varname exists and isn't null, return word; otherwise return null
${varname:offset:length}     # performs substring expansion. It returns the substring of $varname starting at offset and up to length characters

${variable#pattern}          # if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest
${variable##pattern}         # if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest
${variable%pattern}          # if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest
${variable%%pattern}         # if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest
${variable/pattern/string}   # the longest match to pattern in variable is replaced by string. Only the first match is replaced
${variable//pattern/string}  # the longest match to pattern in variable is replaced by string. All matches are replaced

${#varname}                  # returns the length of the value of the variable as a character string

*(patternlist)               # matches zero or more occurrences of the given patterns
+(patternlist)               # matches one or more occurrences of the given patterns
?(patternlist)               # matches zero or one occurrence of the given patterns
@(patternlist)               # matches exactly one of the given patterns
!(patternlist)               # matches anything except one of the given patterns

$(UNIX command)              # command substitution: runs the command and returns standard output


##############################################################################
# FUNCTIONS
##############################################################################


# The function refers to passed arguments by position (as if they were positional parameters), that is, $1, $2, and so forth.
# $@ is equal to "$1" "$2"... "$N", where N is the number of positional parameters. $# holds the number of positional parameters.


function functname() {
  shell commands
}

unset -f functname  # deletes a function definition
declare -f          # displays all defined functions in your login session


##############################################################################
# FLOW CONTROLS
##############################################################################


statement1 && statement2  # and operator
statement1 || statement2  # or operator

-a                        # and operator inside a test conditional expression
-o                        # or operator inside a test conditional expression

# STRINGS

str1 = str2               # str1 matches str2
str1 != str2              # str1 does not match str2
str1 < str2               # str1 is less than str2 (alphabetically)
str1 > str2               # str1 is greater than str2 (alphabetically)
-n str1                   # str1 is not null (has length greater than 0)
-z str1                   # str1 is null (has length 0)

# FILES

-a file                   # file exists
-d file                   # file exists and is a directory
-e file                   # file exists; same -a
-f file                   # file exists and is a regular file (i.e., not a directory or other special type of file)
-r file                   # you have read permission
-s file                   # file exists and is not empty
-w file                   # your have write permission
-x file                   # you have execute permission on file, or directory search permission if it is a directory
-N file                   # file was modified since it was last read
-O file                   # you own file
-G file                   # file's group ID matches yours (or one of yours, if you are in multiple groups)
file1 -nt file2           # file1 is newer than file2
file1 -ot file2           # file1 is older than file2

# NUMBERS

-lt                       # less than
-le                       # less than or equal
-eq                       # equal
-ge                       # greater than or equal
-gt                       # greater than
-ne                       # not equal

if condition
then
  statements
[elif condition
  then statements...]
[else
  statements]
fi

for x in {1..10}
do
  statements
done

for name [in list]
do
  statements that can use $name
done

for (( initialisation ; ending condition ; update ))
do
  statements...
done

case expression in
  pattern1 )
    statements ;;
  pattern2 )
    statements ;;
esac

select name [in list]
do
  statements that can use $name
done

while condition; do
  statements
done

until condition; do
  statements
done

##############################################################################
# COMMAND-LINE PROCESSING CYCLE
##############################################################################


# The default order for command lookup is functions, followed by built-ins, with scripts and executables last.
# There are three built-ins that you can use to override this order: `command`, `builtin` and `enable`.

command  # removes alias and function lookup. Only built-ins and commands found in the search path are executed
builtin  # looks up only built-in commands, ignoring functions and commands found in PATH
enable   # enables and disables shell built-ins

eval     # takes arguments and run them through the command-line processing steps all over again


##############################################################################
# INPUT/OUTPUT REDIRECTORS
##############################################################################


cmd1|cmd2  # pipe; takes standard output of cmd1 as standard input to cmd2
< file     # takes standard input from file
> file     # directs standard output to file
>> file    # directs standard output to file; append to file if it already exists
>|file     # forces standard output to file even if noclobber is set
n>|file    # forces output to file from file descriptor n even if noclobber is set
<> file    # uses file as both standard input and standard output
n<>file    # uses file as both input and output for file descriptor n
n>file     # directs file descriptor n to file
n<file     # takes file descriptor n from file
n>>file    # directs file description n to file; append to file if it already exists
n>&        # duplicates standard output to file descriptor n
n<&        # duplicates standard input from file descriptor n
n>&m       # file descriptor n is made to be a copy of the output file descriptor
n<&m       # file descriptor n is made to be a copy of the input file descriptor
&>file     # directs standard output and standard error to file
<&-        # closes the standard input
>&-        # closes the standard output
n>&-       # closes the ouput from file descriptor n
n<&-       # closes the input from file descripor n


##############################################################################
# PROCESS HANDLING
##############################################################################


# To suspend a job, type CTRL+Z while it is running. You can also suspend a job with CTRL+Y.
# This is slightly different from CTRL+Z in that the process is only stopped when it attempts to read input from terminal.
# Of course, to interrupt a job, type CTRL+C.

myCommand &  # runs job in the background and prompts back the shell

jobs         # lists all jobs (use with -l to see associated PID)

fg           # brings a background job into the foreground
fg %+        # brings most recently invoked background job
fg %-        # brings second most recently invoked background job
fg %N        # brings job number N
fg %string   # brings job whose command begins with string
fg %?string  # brings job whose command contains string

kill -l      # returns a list of all signals on the system, by name and number
kill PID     # terminates process with specified PID

ps           # prints a line of information about the current running login shell and any processes running under it
ps -a        # selects all processes with a tty except session leaders

trap cmd sig1 sig2  # executes a command when a signal is received by the script
trap "" sig1 sig2   # ignores that signals
trap - sig1 sig2    # resets the action taken when the signal is received to the default

disown <PID|JID>    # removes the process from the list of jobs

wait                # waits until all background jobs have finished


##############################################################################
# TIPS & TRICKS
##############################################################################


# set an alias
cd; nano .bash_profile
> alias gentlenode='ssh admin@gentlenode.com -p 3404'  # add your alias in .bash_profile

# to quickly go to a specific directory
cd; nano .bashrc
> shopt -s cdable_vars
> export websites="/Users/username/Documents/websites"

source .bashrc
cd $websites


##############################################################################
# DEBUGGING SHELL PROGRAMS
##############################################################################


bash -n scriptname  # don't run commands; check for syntax errors only
set -o noexec       # alternative (set option in script)

bash -v scriptname  # echo commands before running them
set -o verbose      # alternative (set option in script)

bash -x scriptname  # echo commands after command-line processing
set -o xtrace       # alternative (set option in script)

trap 'echo $varname' EXIT  # useful when you want to print out the values of variables at the point that your script exits

function errtrap {
  es=$?
  echo "ERROR line $1: Command exited with status $es."
}

trap 'errtrap $LINENO' ERR  # is run whenever a command in the surrounding script or function exits with non-zero status 

function dbgtrap {
  echo "badvar is $badvar"
}

trap dbgtrap DEBUG  # causes the trap code to be executed before every statement in a function or script
# ...section of code in which the problem occurs...
trap - DEBUG  # turn off the DEBUG trap

function returntrap {
  echo "A return occurred"
}

trap returntrap RETURN  # is executed each time a shell function or a script executed with the . or source commands finishes executing

docker-tips.sh

##############################################################################
# DOCKER
##############################################################################


docker build -t friendlyname .              # Create image using this directory's Dockerfile
docker run -p 4000:80 friendlyname          # Run "friendlyname" mapping port 4000 to 80
docker run -d -p 4000:80 friendlyname       # Same thing, but in detached mode
docker exec -it [container-id] bash         # Enter a running container
docker ps                                   # See a list of all running containers
docker stop <hash>                          # Gracefully stop the specified container
docker ps -a                                # See a list of all containers, even the ones not running
docker kill <hash>                          # Force shutdown of the specified container
docker rm <hash>                            # Remove the specified container from this machine
docker rm $(docker ps -a -q)                # Remove all containers from this machine
docker images -a                            # Show all images on this machine
docker rmi <imagename>                      # Remove the specified image from this machine
docker rmi $(docker images -q)              # Remove all images from this machine
docker login                                # Log in this CLI session using your Docker credentials
docker tag <image> username/repository:tag  # Tag <image> for upload to registry
docker push username/repository:tag         # Upload tagged image to registry
docker run username/repository:tag          # Run image from a registry
docker system prune                         # Remove all unused containers, networks, images (both dangling and unreferenced), and optionally, volumes. (Docker 17.06.1-ce and superior)
docker system prune -a                      # Remove all unused containers, networks, images not just dangling ones (Docker 17.06.1-ce and superior)


##############################################################################
# DOCKER COMPOSE
##############################################################################


docker-compose up                               # Create and start containers
docker-compose up -d                            # Create and start containers in detached mode
docker-compose down                             # Stop and remove containers, networks, images, and volumes
docker-compose logs                             # View output from containers
docker-compose restart                          # Restart all service
docker-compose pull                             # Pull all image service 
docker-compose build                            # Build all image service
docker-compose config                           # Validate and view the Compose file
docker-compose scale <service_name>=<replica>   # Scale special service(s)
docker-compose top                              # Display the running processes


##############################################################################
# DOCKER SERVICES 
##############################################################################


docker service create <options> <image> <command>   # Create new service
docker service inspect --pretty <service_name>      # Display detailed information Service(s)
docker service ls                                   # List Services
docker service ps                                   # List the tasks of Services
docker service scale <service_name>=<replica>       # Scale special service(s)
docker service update <options> <service_name>      # Update Service options


##############################################################################
# DOCKER STACK 
##############################################################################


docker stack ls                                 # List all running applications on this Docker host
docker stack deploy -c <composefile> <appname>  # Run the specified Compose file
docker stack services <appname>                 # List the services associated with an app
docker stack ps <appname>                       # List the running containers associated with an app
docker stack rm <appname>                       # Tear down an application


##############################################################################
# DOCKER MACHINE
##############################################################################


docker-machine create --driver virtualbox myvm1                           # Create a VM (Mac, Win7, Linux)
docker-machine create -d hyperv --hyperv-virtual-switch "myswitch" myvm1  # Win10
docker-machine env myvm1                                                  # View basic information about your node
docker-machine ssh myvm1 "docker node ls"                                 # List the nodes in your swarm
docker-machine ssh myvm1 "docker node inspect <node ID>"                  # Inspect a node
docker-machine ssh myvm1 "docker swarm join-token -q worker"              # View join token
docker-machine ssh myvm1                                                  # Open an SSH session with the VM; type "exit" to end
docker-machine ssh myvm2 "docker swarm leave"                             # Make the worker leave the swarm
docker-machine ssh myvm1 "docker swarm leave -f"                          # Make master leave, kill swarm
docker-machine start myvm1                                                # Start a VM that is currently not running
docker-machine stop $(docker-machine ls -q)                               # Stop all running VMs
docker-machine rm $(docker-machine ls -q)                                 # Delete all VMs and their disk images
docker-machine scp docker-compose.yml myvm1:~                             # Copy file to node's home dir
docker-machine ssh myvm1 "docker stack deploy -c <file> <app>"            # Deploy an app

kubernetes-tips.sh

##############################################################################
# KUBERNETES
# PDF: https://sematext.com/kubernetes-cheat-sheet/
# WEBSITE: https://kubernetes.io/
# DOCUMENTATION: https://kubernetes.io/docs/home
##############################################################################


##############################################################################
# CLIENT CONFIGURATION
##############################################################################


# Setup autocomplete in bash; bash-completion package should be installed first
source <(kubectl completion bash)

# View Kubernetes config
kubectl config view

# View specific config items by json path
kubectl config view -o jsonpath='{.users[?(@.name == "k8s")].user.password}'

# Set credentials for foo.kuberntes.com
kubectl config set-credentials kubeuser/foo.kubernetes.com --username=kubeuser --password=kubepassword


##############################################################################
# VIEWING, FINDING RESOURCES
##############################################################################


# List all services in the namespace
kubectl get services

# List all pods in all namespaces in wide format
kubectl get pods -o wide --all-namespaces

# List all pods in json (or yaml) format
kubectl get pods -o json

# Describe resource details (node, pod, svc)
kubectl describe nodes my-node

# List services sorted by name
kubectl get services --sort-by=.metadata.name

# List pods sorted by restart count
kubectl get pods --sort-by='.status.containerStatuses[0].restartCount'

# Rolling update pods for frontend-v1
kubectl rolling-update frontend-v1 -f frontend-v2.json

# Scale a replicaset named 'foo' to 3
kubectl scale --replicas=3 rs/foo

# Scale a resource specified in "foo.yaml" to 3
kubectl scale --replicas=3 -f foo.yaml

# Execute a command in every pod / replica
for i in 0 1; do kubectl exec foo-$i -- sh -c 'echo $(hostname) > /usr/share/nginx/html/index.html'; done


##############################################################################
# MANAGE RESOURCES
##############################################################################


# Get documentation for pod or service
kubectl explain pods,svc

# Create resource(s) like pods, services or daemonsets
kubectl create -f ./my-manifest.yaml

# Apply a configuration to a resource
kubectl apply -f ./my-manifest.yaml

# Start a single instance of Nginx
kubectl run nginx --image=nginx

# Create a secret with several keys
cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Secret
metadata:
 name: mysecret
type: Opaque
data:
 password: $(echo "s33msi4" | base64)
 username: $(echo "jane"| base64)
EOF

# Delete a resource
kubectl delete -f ./my-manifest.yaml


##############################################################################
# MONITORING & LOGGING
##############################################################################


# Show metrics for nodes
kubectl top node

# Show metrics for pods
kubectl top pod

# Show metrics for a given pod and its containers
kubectl top pod pod_name --containers

# Dump pod logs (stdout)
kubectl logs pod_name

# Stream pod container logs (stdout, multi-container case)
kubectl logs -f pod_name -c my-container