Written by Demitri Muna ([email protected])

This is a collection of tips and tricks for working in a terminal environment. The program where you enter commands is called a shell. These commands are applicable to the bash shell (/usr/bin/bash) unless otherwise indicated.

~/: represents your home directory, e.g.

% cd ~
% mv ~/file_in_home_dir /some/other/place/

Start typing a few characters of a file or directory, e.g.

% cd Docu

and then hit the tab key. The shell will automatically complete the file (or directory) name that matches the start of what you typed. This is very useful for files with long names. The shell will complete until there is no longer a unique match. For example, if a diectory has these files:

plateInput_047-25_MGA_SCI_8188-output.par
plateInput_047-25_MGA_SKY_8188-output.par
plateInput_047-25_MGA_STA_8188-output.par

entering ls pl then tab will result in this at the prompt:

% ls plateInput_047-25_MGA_S

One more character, then tab will complete the filename.

By default, tab completion is case-sensitive, but it's much more useful (and forgiving) to be case-insensitive. Place this ~/.bashrc to ignore case in tab completion:

set completion-ignore-case on

Same in tcsh (~/.tcshrc):

set complete = enhance

After hitting tab to autocomplete, if the shell finds more than one file that is not unique, hit tab again to list them.

In addition to tab completion, you can customize the behavior to auto-complete from a limited list of values specific to a certain program.

Place this in your ~/.bashrc. Typing ssh h plus tab will autocomplete host names found in your ~/.ssh/config file. (Bonus points for anyone who can do this via Python instead.)

function _ssh_completion() {
    perl -ne 'print "$1 " if /^Host (.+)$/' ~/.ssh/config
}
complete -W "$(_ssh_completion)" ssh

This can be expanded to any command, e.g.

function _svn_completion() {
    echo "add blame cat changelist checkout cleanup commit copy delete diff export help import info list lock log merge mergeinfo mkdir move patch propdel propedit propget proplist propset relocate resolve resolved revert status switch unlock update"
	# left out "upgrade"
}
complete -W "$(_svn_completion)" svn

For when typing "notebook" is just more trouble than it's worth:

function _jupyter_completion() {
	echo "notebook --pdb"
}
complete -W "$(_jupyter_completion)" jupyter

And for ipython notebook:

function _ipython_completion() {
	echo "notebook --pdb"
}
complete -W "$(_ipython_completion)" ipython

Create an alias with the command (shortcut=command)

alias ll="ls -l"

It's recommended to put all your aliases in their own file, e.g. ~/.aliases, which is then called from ~/.bashrc as:

source $HOME/.aliases

Use !! to represent the last command that was run, can be used to make a new command:

cat some_file.txt
!! | grep string

Also very useful with sudo:

rm file # permission denied
sudo !!

Create a new file with no editor

% cat > delme
Enter text here
over several lines if needed
that will be placed into the new file 'delme'. 

To exit the editing mode, enter cntrl-d on a blank line. Note if the file already exists, it will be overwritten! You can also append to a file with cat >> filename.

Use \ to work with spaces in filenames, e.g.

cd Library/Application\ Support

Alternatively, you don't need to escape spaces if you put the filename in quotes:

cd "Library/Application Support"

This works particularly well with tab completion which will do the right thing.

Multiple files can be selected with regular expression patterns:

ls file[12348]

is the equivalent of

ls file1 file2 file3 file4 file8

The top command shows all processes running as well as memory and CPU usage. It's the first stop to check how your system is doing. The program Activity Monitor does a very similar thing on macOS.

How to kill a process that has hung. List all active processes:

% ps

Identify the process ID (PID) of the program you want to force quit (from top or similar), and run:

% kill -9 PID_OF_PROCESS

paste : concatenate line-matched files by columns (http://en.wikipedia.org/wiki/Paste_%28Unix%29)

Truncate a file to zero length without deleting it. This allows programs using the file open to keep reading and writing it.

% >longfile.log

After you mistype a command, use this to replace "wrong" with "right" and re-execute the command.

% ^wrong^right

In you are working on a remote machine through a terminal, you can create a virtual window using the screen command. This virtual window will continue to run even if your connection with that machine dies or you shut down your laptop (as long as you detach the screen first). Works in Unix and Mac OS X.

(There are other commands, but these are the only three you need, google “Unix screen”.)

This command will use the speech synthesizer to say the string passed to it.

% say "text that will be spoken by the speech synthesizer"

Similarly, afplay will play audio files.

Install eSpeak on Linux:

sudo apt-get install espeak

Usage:

espeak "text that will be spoken by the speech synthesizer"

This may seem like a toy, but it has some nice uses. Let's say you are running a long process and want to get an audible signal when it's finished:

log_script.py; say "script finished!"

Examples:

% ls -l | pbcopy
% pbpaste | gzip > data.gz

From the Finder (or any open/save dialog box), type command-shift-g. A navigation box will appear where you can type the path you want to go to, complete with tab completion. (Not perfect tab completion; if you complete on the first match it finds, even if there are others). You can also use ~ to specify the home directory.

Direct output to a file, e.g.

ls -l > listing.txt

gzip output on the fly:

some process that produces output | gzip > output_file.gz

app 2>&1 : combine standard out with standard error when running app, useful if you are piping the output for example

Example script to customize (and color) your prompt

# See link for full reference:
#
# http://bash-hackers.org/wiki/doku.php/scripting/terminalcodes
#
# \033 indicates a control character is to follow
#
# For full list, "man bash" and search to 2nd "PROMPTING" or see:
# http://tldp.org/HOWTO/Bash-Prompt-HOWTO/bash-prompt-escape-sequences.html
# also: http://www.yolinux.com/HOWTO/Bash-Prompt-HOWTO.html
#
# \u : username
# \h : host to first "."
# \w : current full working directory
# \W : last part of path

# ALL control sequences (i.e. non-printing characters)
# MUST start with a \[ and end with a \]. This tells
# the shell that these are control characters.
# One set of escaped brackets can be used for several
# in a row, but can be done for each alone as defined
# below. If this is not done the line wrap will not
# function properly (since the shell doesn't know how
# long the prompt is).

COL_BLACK=$'\[\033[30m\]'
COL_RED=$'\[\033[31m\]'
COL_GREEN=$'\[\033[32m\]'
COL_YELLOW_ORANGE=$'\[\033[33m\]'
COL_BLUE=$'\[\033[34m\]'
COL_MAGENTA=$'\[\033[35m\]'
COL_CYAN=$'\[\033[36m\]'
COL_NORM=$'\[\033[39m\]'
PMPT_BOLD=$'\[\033[1m\]'
PMPT_NORM=$'\[\033[0m\]'

# See: http://networking.ringofsaturn.com/Unix/Bash-prompts.php
# for a longer list of colours.

# actual command that sets prompt

PS1="${PMPT_BOLD}${COL_CYAN}\h${COL_NORM} [\w] %${PMPT_NORM} "

Example result (but in color):

MacBook-Air [~/Documents/Repositories/] %

Web-based graphical tools to construct a custom prompt:

• http://omar.io/ps1gen/
• https://www.kirsle.net/wizards/ps1.html
• http://ezprompt.net
• http://bashrcgenerator.com

Script(s) to add a line separator between each command in bash:

• http://www.techlw.com/2012/04/add-separator-line-between-commands-on.html
• http://www.malloc.co/terminal/add-a-separator-between-commands-in-terminal/

http://stackoverflow.com/questions/68372/what-is-your-single-most-favorite-command-line-trick-using-bash
http://unix.stackexchange.com/questions/6/what-are-your-favorite-command-line-features-or-tricks
http://www.reddit.com/r/bashtricks
http://www.linuxjournal.com/article/7385