Bash bits

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

» Bash shebang

Specify the explicit path:

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#!/bin/bash

Let the environment decide:

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#!/usr/bin/env bash

Explanation: Alec Bennett

» Fail fast … and more

Best added directly after the shebang.

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

or in short:

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set -xueo 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)

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echo $?

Examples:

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> true; echo $?
0

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> false; echo $?
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» Constants

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

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readonly systems=( windows linux darwin  )

Reference: Jeff Lindsay et al. - bashstyle

» Strings equal check

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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

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readonly systems=( windows linux darwin  )

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

Reference: Vivek Gite

» Loop until failure

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while <command to execute> ; do :; done

Reference: nneonneo & Gurpreet Atwal

» Redirect Output

» Redirect Stdout

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command > stdout.txt

» Redirect Stderr

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command 2> stderr.txt

Reference: How to Redirect Stderr in Bash

» Redirect Stdout and Stderr

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command 2>&1 > output.txt

Reference: BASH Shell Redirect Output and Errors