using if and a boolean function in bash script: if condition evaluates to false when function returns true

Question

is_dir_empty(){

    for file in "$1"
    do
        if [ "$file" != "$1" ]; then
            return 0
        fi
    done
    echo "return 1"
    return 1
}

file="/home/tmp/*.sh"

if is_dir_empty "$file"; then
    echo "empty"
else echo "not empty"
fi

it outputs

return 1
not empty

so is_dir_empty returned 1 but if condition evaluated to false somehow.... why?

Possible duplicate of [bash functions: return boolean to be used in if](http://stackoverflow.com/questions/5431909/bash-functions-return-boolean-to-be-used-in-if) — Mad Physicist, Feb 01 '16 at 19:09

score 9 · Accepted Answer · answered Feb 05 '13 at 01:47

9

Because shell scripts follow the Unix convention of expecting utilities to return zero for success and non-zero for failure, so boolean conditions are inverted.

answered Feb 05 '13 at 01:47

Michael Day

937
6
12

that other guy · Answer 2 · 2017-10-23T16:36:38.500

2

Globs are not expanded in double quotes, so you're always comparing against the literal value /home/tmp/*.sh. Unquote $1 in the for loop, and it'll word split and glob expand into a list of .sh files (this online tool would have pointed this out automatically).

Also, unlike in C, zero is considered success and non-zero failure.

edited Oct 23 '17 at 16:36

answered Feb 05 '13 at 01:53

that other guy

109,738
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185

The online tool looks like it would have been useful, is there an equivalent that is up today? – Stuart Axon Oct 23 '17 at 14:58
1

@StuartAxon Today there's ShellCheck. It has an online version and can also be installed locally – that other guy Oct 23 '17 at 16:41

score 0 · Answer 3 · answered Feb 05 '13 at 07:18

0

you can check if a directory is empty by:

[ "$(ls -A /path/to/directory)" ] && echo "Not Empty" || echo "Empty"

answered Feb 05 '13 at 07:18

Hamid Reza Moradi

399
2
3
11

using if and a boolean function in bash script: if condition evaluates to false when function returns true

3 Answers3