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.

Outline

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

Terminals are old

GiraffeNerve

https://commons.wikimedia.org/wiki/File:GiraffaRecurrEn.svg

Teletype

https://commons.wikimedia.org/wiki/File:Teletype.jpg

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:

  WARN_COLOUR="\033[031m"
  RESET_COLOUR="\033[039m"
  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

prompt1

prompt2

prompt3

PS1

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

PROMPT_COMMAND

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

You can use readline in your own programs
You can even use readline to wrap other programs that don’t support it out of the box – rlwrap https://github.com/hanslub42/rlwrap
For python projects, also check out prompt-toolkit https://github.com/jonathanslenders/python-prompt-toolkit

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:

./ma...
./magic
./magical

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
   ^[[A

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"
    HISTFILESIZE=1000000000
    HISTSIZE=1000000

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: http://wiki.bash-hackers.org/syntax/pe

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

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

Functions

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

Using the terminal effectively

Outline

Terminals are old

Fancier terminals

Escape codes

Using colours

Customising the prompt

PS1

PROMPT_COMMAND

Movement on the command line

GNOME is annoying

Editing commands

Magic of readline

Quick aside

Movement through history

Working out keycodes

Quick aside

History expansion

Keeping history

The problem with multiple terminals

Tab completion

Command substitution

Actually useful example

Process substitution

Another way of joining programs together

Variable substitution

Curly brace expansion

Aliases

`ls` family

Functions

Useful example

Find idioms

Different ways of grepping files from `find`

Different shells

Further reading

Outline

Terminals are old

Fancier terminals

Escape codes

Using colours

Customising the prompt

PS1

PROMPT_COMMAND

Movement on the command line

GNOME is annoying

Editing commands

Magic of readline

Quick aside

Movement through history

Working out keycodes

Quick aside

History expansion

Keeping history

The problem with multiple terminals

Tab completion

Command substitution

Actually useful example

Process substitution

Another way of joining programs together

Variable substitution

Curly brace expansion

Aliases

ls family

Functions

Useful example

Find idioms

Different ways of grepping files from find

Different shells

Further reading

`ls` family

Different ways of grepping files from `find`