Bash detect 1st input parameter is "debug"?

Question

I want to detect if the 1st bash input parameter is "debug"(string).

I write script like this:

#! /usr/bin/env bash

if [ "$#" -eq "1" && "$1" -eq "debug" ]; then
    echo "hello debug"
fi

Error message:

line 3: [: missing `]'

I don't know why, please help.

There's no real need to test $# here; you can ignore additional arguments if present, and if $# is 0, then "$1" = debug will be false since $1 expands to the empty string. — chepner
– chepner, Commented Jun 13, 2019 at 2:10

vlumi · Accepted Answer · 2019-06-13 02:01:11Z

5

Compare strings with ==, -eq is an arithmetic operator. Also, within [] you have to use the -a operator instead of &&, or split it in two. Here are a few different ways to write the same thing:

if [[ $# -eq 1 && "$1" == "debug" ]] ; then
    echo "hello debug"
fi

if [[ "$#" == "1" && "$1" == "debug" ]] ; then
    echo "hello debug"
fi

if [ "$#" == "1" ] && [ "$1" == "debug" ] ; then
    echo "hello debug"
fi

if [ "$#" == "1" -a "$1" == "debug" ] ; then
    echo "hello debug"
fi

answered Jun 13, 2019 at 2:01

vlumi

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1 Comment

chepner Over a year ago

Splitting in two is preferable; -a is non-standard and considered obsolete by POSIX.

Joseph Sible-Reinstate Monica · Accepted Answer · 2023-08-21 23:40:15Z

2

Instead of [ "$#" -eq "1" && "$1" -eq "debug" ], use either [ "$#" -eq "1" ] && [ "$1" -eq "debug" ] (recommended; see https://www.shellcheck.net/wiki/SC2166) or [ "$#" -eq "1" -a "$1" -eq "debug" ]. The problem is that && is bash's way of saying "and", rather than -a, which is test's way of saying "and". You can't use a bash "and" inside of test.

edited Aug 21, 2023 at 23:40

answered Jun 13, 2019 at 1:43

Joseph Sible-Reinstate Monica

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