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shell

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created  2023/06/01
modified 2023/07/08
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notes on shell scripting

*nix

batch

shebang

a shebang or hangbang is the character sequence at the beginning of a script denoting what interpreter to use, it is a hashtag followed by an exclaimation mark then the path to the executable of the interpreter of the scripting language in the format `#!interpreter [args]`

so if we have script.sh with a shebang to call the sh binary with a few arguments

#!/bin/sh -x -y

echo Hello World!

when we run it with

./script.sh a b

it gets executed as

/bin/sh -x -y ./script.sh a b

examples

!/usr/bin/env sh

→ use the bourne shell, most portable

!/bin/sh

→ use the bourne shell

!/bin/bash

→ use the bourne again shell

!/usr/bin/pwsh

→ use powershell

!/bin/false

→ do nothing when called by a user and return a non-zero exit code

bourne vs bourne again shell

the simple difference between sh and bash is that sh is completely portable across all *nix distributions and bash has a few extensions from gnu added to it, there are also other shells that are less common with more liberal extensions

cheat sheet

TODO: write shell script language cheatsheet