This week, Peter through some tips and tricks for upping your terminal game. Find out how to quickly search through your command history, make a fancy, colourful prompt, and some magic shortcut keys you definitely didn’t know about!

You can find the original slides for this talk here.


  • Escape codes
  • Customising the prompt
  • The command line and readline
  • History
  • Command, process and variable substitutions
  • Aliases and functions

Terminals are old



Fancier terminals

  • konsole
  • terminology
  • terminator
  • guake
  • tilda
  • rxvt-unicode
  • xterm
  • cool-retro-term

Escape codes

  • Also known as control characters
  • “In-band signalling”
  • Terminal would intercept these and do something else instead of printing them
  • Cover things like backspace, ringing the bell, newline, etc.
  • Also allowed setting text attributes: bold, underscore, different colours
  • Because they aren’t designed for printing, they might be hard to type, or look a bit odd. Many include the ESC character (hence the name):
  \033[030m         ^[[30m
  ESC [ 3 0 m       \e[30m
  • ^[” is the code for C-[, which is also ESC or \e (0x1b, 033 in octal)
  • Actually many different types of terminals, that support different control character sets. We’re normally interested in “xterm-256color” and “ANSI” escape sequences
    • Look under /usr/share/terminfo for a few other examples…

Using colours

  • Set foreground colour with “\033[03<0-8>m”, and reset with “\033[039m
  • Set background colour with “\033[04<0-8>m”, and reset with “\033[049m
  • Normally just put all the colours into variables and reference them:
  echo -e "${WARN_COLOUR}WARNING: badness${RESET_COLOUR}"
  • Can use these colours in anything that writes to terminal (even Fortran!)
  character(len=*), parameter :: red = char(27) // "[031m"
  character(len=*), parameter :: reset = char(27) // "[039m"
  print*, red // "WARNING: badness" // reset

Customising the prompt






  • Default value is \s-\v\$
  • Lots of options: info bash -n Controlling to see full list
  • [\t] \u@\h \w: turns into [15:27:30] user@hostname ~/directory:
  • To use colours, we need to surround them with an additional \[ and \]
  • This lets bash know that they won’t take any space up on screen


  • This is a command that is run every time before displaying the prompt
  • You can use this to show you information about e.g the git repo you are in, or the number of jobs you have running on a supercomputer

Movement on the command line

  • readline is the secret hero here
  • Readline provides many, many commands for moving about on the command line
  • info readline to find out more
  • Follow the basic Emacs commands
  • C- means “Ctrl”, M- means “Alt” (used to be “Meta”)
  • C-a/C-e: move to beginning/end of line
  • M-f/M-b: move forward/backward by a word
  • Shift-PgUp/Shift-PgDown: scroll backwards/forwards

GNOME is annoying

  • In GNOME, the default terminal grabs the Alt key
  • Turn this off: Edit > Keyboard Shortcuts…, uncheck “Enable menu access keys”

Editing commands

  • M-d to delete the following word
  • C-k to delete from the cursor to the end of the line
  • C-u to delete from the cursor to the beginning of the line
    • Also works in lots of other places in Linux!
  • M-# to comment out a line
  • Fix a mistake on the previous line by running ^a^b^ to replace the first instance of “a” with “b” and then rerun the command
    • Also useful for rerunning a command with a different parameter
  • If a command is becoming long and hard to edit, you can open it in your $EDITOR with C-x C-e
    • For Emacs, the best thing to do is set $EDITOR to emacsclient and M-x start-server in Emacs – this will then cause things to pop-up in your existing Emacs session

Magic of readline

Quick aside

Movement through history

  • Search with C-r
  • You can also enable a fancier search. Put the following in your ~/.inputrc:
"\e[A": history-search-backward
"\e[B": history-search-forward
  • Reload your inputrc with C-x C-r
  • Now you can start typing a previous command and then use the cursor keys to browse all commands that start with those letters:

Working out keycodes

Quick aside

  • Quickest way to work out what keycode to put is to run sed -n l then hit the key and press enter:
   sed -n l

History expansion

  • Special variables for referring to previous commands, all start with “!
    • This is why you might struggle to use “!” in commands/strings
  • !!: Repeat the previous command
  • !N: Refer to command on line N
  • !-N: Refer to the command N lines back
  • !foo: Refer to the last command starting with “foo”
  • !$: Use the value of the last argument from the previous command
  • You can also insert the last argument from the previous command with M-.
    • Except on Macs, where you need to do ESC-., or change how option works
    • You can also prefix with a number: M-2 M-. to get the second argument (with zero being the previous command)

Keeping history

The problem with multiple terminals

  • If you use multiple terminals, their histories get out of sync
  • By default, only the history from last one open is kept!
  • Easy fix: append to the history file on every command:
    shopt -s histappend
    PROMPT_COMMAND="history -a"
  • Last two commands just make sure we keep a lot of history…

Tab completion

  • Hit TAB to auto-complete commands and filenames
  • maybe you’re lazy like me, and don’t care about capitalisations in filenames, etc. Put the following in your ~/.inputrc:
set completion-ignore-case On
TAB: complete
"\e[Z": menu-complete
  • Super useful when traversing the filesystem!

Command substitution

  • Use the output of one command in another one: $(command)
    • You can also use backticks, but $() is better
  • Nest them!
echo $(ls $(echo foo))

Actually useful example

    which pip
    less $(!!)
  • Find out where a command is installed (is it a system package, or something I’ve installed myself?)
  • Assuming I think it’s a script, have a look at its contents

Process substitution

Another way of joining programs together

  • How to compare the output of running two different programs?
  • Could just dump the output of each program into separate files and then diff them
    • This is boring
  • Better way is “process substitution”:
  diff <(command1) <(command2)
  diff <(command1 | sort | uniq) <(command2 | sort | uniq)
  diff <(ssh archer 'cat remote/file') local_file
  • Connects the output of the “inner” commands with the input argument of the “outer” command

Variable substitution

  • Bash has some fancy uses for curly braces:
  • Drop the extension from a filename: ${foo%.*}
  • Or replace it with a different one: ${foo/tex/pdf}
  • Get the length of a string: ${#foo}
  • Read more:

Curly brace expansion

  • Quick way to iterate over a few options: {a,b,c} gives a b c
  • a{b,c}d gives abd acd
  • Useful for installing multiple packages:
    • sudo apt install {lapack,hdf5}-dev
    • will install both the lapack and hdf5 development packages
  • Copying one file to another:
    • cp filename{,.bak}
  • Also does ranges: {1..10} gives numbers 1 to 10, {a..z} gives…


  • Aliases are “another name” for a command
  • Useful if you always run a command with the same options

ls family

alias ls='ls -hF --color'   # add colors for filetype recognition
alias la='ls -Alh'          # show hidden files
alias lt='ls -ltrh'         # sort by date, most recent last


  • Use functions for more complicated expressions
  • If you find yourself writing particularly complicated bash, stop! Use a better language instead!

Useful example

function latest() {
    # Print the most recent file in a given directory
    lastfile=$(ls -tc --color=tty "$@" | head -1);
    echo "$@$lastfile";

# Move the last file I downloaded here
mv -v "$(latest ~/Downloads)" .

Find idioms

Different ways of grepping files from find

find path/ -type f -exec grep foo {} \;
find path/ -type f | xargs grep foo
for f in $(find path/ -type f); do grep foo $f; done

Different shells

  • ksh if you want more POSIX
  • zsh if you want to be like Ed
  • fish if you want to really stand out
  • tcsh if you want to die inside
  • xonsh if you really, really like python

Further reading