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Some helpful Bash bits

 2 years ago
source link: https://simjue.pages.dev/post/2022/bash-bits/
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first published: 2022-08-08

Another post with stuff I can’t remember or might forget again 🤷‍♂️

» Bash shebang

Specify the explicit path:

#!/bin/bash

Let the environment decide:

#!/usr/bin/env bash

Explanation: Alec Bennett

» Fail fast … and more

Best added directly after the shebang.

set -o errexit  # fail if a call exits with non-zero
set -o nounset  # fail if an unset variable is used
set -o xtrace   # output every line which gets executed
set -o pipefail # fail if a command in a pipe fails

or in short:

set -euxo pipefail

Reference: GNU Bash Manual - the set builtin

» Exit code of last execution

Check with $? if the last executed program failed (0 = ok, everything else = failed)

echo $?

Examples:

> true; echo $?
0

> false; echo $?
1

» Constants

Use readonly. For example, a fixed array of OS names:

readonly systems=( windows linux darwin  )

Reference: Jeff Lindsay et al. - bashstyle

» Strings equal check

if [[ "$str1" == "$str2" ]]; then
    echo "Strings are equal"
else
    echo "Strings are not equal"
fi

Reference: tecadmin.net - Check if two strings are equal

» For Loops

readonly systems=( windows linux darwin  )

for system in "${systems[@]}"; do
    echo "system: $system"
done

Reference: Vivek Gite


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