shells - jasper-zanjani/dotfiles GitHub Wiki

Shells

bash

getopt and argp_parse reorder the elements of argv by default, but this behavior can be suppressed by setting the _POSIX_OPTION_ORDER environment variable

Terminal prompt

ANSI/VT100 terminals and emulators can display colors and formatted texts by using escape sequences ( escape character followed by format code, terminated by "m").
Three escape characters:

\e
\033
\x1B

Syntax

Event designator	Effect
`!^`	first argument from previous command
`!$`	last argument from previous command
`^string`	repeat last command, deleting the first instance of {string}
`^string^substitute`	repeat last command, substituting the first instance of {string} with {substitute} (CLKF)
`!!:n`	{n}th argument from previous command
`!#:n`	{n}th word of current command

Syntax	Effect
`$((...))`	arithmetic expansion
`[...]`	alias for `test`
`$(...)`	command substitution
`${...}`	variable substitution
`${var:start:size}`	variable slicing
`filename{,.new}`	brace expansion makes multiple arguments from a single one

Content of all loops is bracketed by do and done: for i in ... do ...; done; and for ((i=0; i<N; i++)); do cmd; done;

for i in {01..07}; do cmd; done;
for i in {000..100}; do cmd; done;
for i in 1 2 3 4 5; do cmd; done;

Number bases	Description
`r#n`	general format for interpreting number as having base (radix)
`2#1111001110011010`	binary
`0x32`	hex numbers
`032`	octal
`32#@_`	base-32: a range of ASCII characters can be used to define numbers with bases up to 64: 10 digits, 26 lowercase characters, 26 uppercase characters, '@', and '_'

Command sequence syntax	Effect
`;`	run commands synchnonously
`&`	run commands asynchronously
`&&`	logical AND; run next command synchronously only if first command succeeds
`

Variables

[3]

Elvish shell

if/else

~> if $true { echo good } else { echo bad }

for loop iterating over an array

~> for x [lorem ipsum] {
     echo $x.pdf
   }

try/catch block and raising an error

~> try {
     fail 'bad error'
   } except e {
     echo error $e
   } else {
     echo ok
   }