Is there any mechanism in Shell script alike “include guard” in C++?

Question

let\'s see an example: in my main.sh, I\'d like to source a.sh and b.sh. a.sh, however, might have already sourced b.sh. Thus it will cause the codes in b.sh executed twice. Is

Answer 1

Personally I usually use

set +o nounset # same as set -u

on most of my scripts, therefore I always turn it off and back on.

#!/usr/bin/env bash

set +u
if [ -n "$PRINTF_SCRIPT_USAGE_SH" ] ; then
    set -u
    return
else
    set -u
    readonly PRINTF_SCRIPT_USAGE_SH=1
fi

If you do not prefer nounset, you can do this

[[ -n "$PRINTF_SCRIPT_USAGE_SH" ]] && return || readonly PRINTF_SCRIPT_USAGE_SH=1