shell command workshop.md

Useful *nix tricks

Commands

General Useful Commands

Put running process to background: Ctrl+Z

Put process back to foreground to continue work: fg

Find string or regexp pattern in files: grep -r 'some_string' path/to/files

Find files by name: find . -name '*.py'

Count how many words, lines and characters a file has: wc

eg. wc -l abc.txt will output how many lines there are in abc.txt

Replace or translate characters: tr

eg. tr "[:lower:]" "[:upper:]" < filename

Replace strings in file based on regexp: sed

eg. sed -i 's/find/replace/g' filename

Make shortcut for files: ln -s filename aliasname

Check disk mounts and remaining disk space: df -h

Check file space usage for a directory: du -h {{directory}}

Or even better: use ncdu

I/O Redirection

Most Linux Command get input from command line and output to the display. But don't have to be.

Input Redirection

use > to a file, if exist, it will overwrite the file.otherwise create one.

ls > file_list.txt

You can use >> character to append out to the file. if not exist, create one.

ls >> file_list.txt

Output Redirection

By default, standard input gets its contents from the keyboard, but like standard output, it can be redirected.

use < to get input stream from a file, like this,

cat < file_list.txt

Pipelines

Heredoc

TODO

tar

awk

< |

pipe while 循环

test 判断

curl

ps

top

kill

netstat or ss?

ifconfig

SSH

How to generate SSH key-pair: ssh-keygen

How to copy your public key to server: ssh-copy-id username@server

How to correctly SSH: ssh -i id_rsa.key username@server

How to save yourself from typing long SSH commands - create a file ~/.ssh/config with 400 permission, content as follows:

Host myserver
    User ubuntu
    HostName 8.8.8.8
    IdentityFile ~/.ssh/MyPrivateKey.pem

After this, you can connect to your server by simply typing: ssh myserver

How to copy files between two computers via SSH: scp filename username@server1.com:/some/dir/

How to use SSH as tunneling proxy: ssh -N -D 1234 server_name (Useful for you-know purpose)

Note: SSH private key permission must not be worldly readable (400 is prefered), otherwise the server will usually refuse it.

Word of advice

Life is short. So:

• If you find yourself doing the same thing again and again - AUTOMATE it!
• Tired of reading extra long man " pages"? Install tl;dr might help. TL;DL == "Too Long; Didn't read"
• Tired of typing long cd like cd /apps/apache2/sites/mysite/htdocs/sites/all/themes/custom/? There is a tool called z that you can simply use like z custom. It will put you there.
• Cool people use Zsh, Vim/Emacs, and tmux.

Please act responsibly. So:

• Do not upload your SSH key and any sensitive information to GitHub
• Do not set global write permissions using chmod.
• Do not rm -rf ./. As you might accidently add a space between . and /. The world as you know it might cease to exist. Please always use rm -rf SOME_SPECIFIC_DIRECTORY_NAME.