GETOPTS parse empty and nonempty args

Question

I am trying to make script that has two switches -h and -d, -d having a mandatory number argument. After it there will be undetermined number of paths to file. So far, I have this, but the code seems to not recognize invalid switch -r (can be any name) and also does not work when I do not input any switches:

while getopts ":hd:" opt; do
case $opt in
    h)
            echo $usage
        exit 0
            ;;
    d)
        shift 2
            if [ "$OPTARG" -eq "$OPTARG" ] ; then # ako dalsi argument mame cislo
            depth=$OPTARG
        fi
            ;;
        \?)
        shift 1
            ;;
        :)
            shift 1
            ;;
esac
done
echo $1

when I type ./pripravne1.sh -d /home/OS/test_pz/test2 I get ./pripravne1.sh: [: /home/OS/test_pz/test2: integer expression expected when I type ./pripravne1.sh -r /home/OS/test_pz/test2 I get only empty string.

score 5 · Accepted Answer · 2018-10-31T21:08:53.073

5

[ "$OPTARG" -eq "$OPTARG" ] ... is not the right way to check if $OPTARG is numeric -- it may print a nasty inscrutable error to the user if that's not the case, or it may just return true in all cases (in ksh), or also return true for an empty $OPTARG (in zsh).

Also, an option taking an argument may be given as either -d12 or -d 12, so a blind shift 2 won't cut it. And doing a shift inside the loop may badly interract with getopts, which is itself using the live argument list.

Taking that into account, this is what I propose:

die(){ echo >&2 "$@"; exit 1; }
usage(){ echo >&2 "usage: $0 [-h] [-d num] files..."; exit 0; }

depth=0

while getopts :hd: opt; do
        case $opt in
        h)      usage ;;
        d)      case $OPTARG in
                ''|*[!-0-9]*|-|*?-*) die "invalid number $OPTARG" ;;
                *) depth=$OPTARG ;;
                esac
                ;;
        :)      die "argument needed to -$OPTARG" ;;
        *)      die "invalid switch -$OPTARG" ;;
        esac
done
shift "$((OPTIND - 1))"

echo depth="$depth"
echo files="$@"

edited Oct 31 '18 at 21:08

answered Oct 22 '18 at 20:39

1

[ being not a special it would not exit the shell. [ would return a non-zero exit status and output an error message if it didn't like an operand to -eq. POSIX says operands are to be decimal integer numbers but doesn't say what should happen if one passes operands that are not, and the behaviour varies between implementation. For instance, with OPTARG='x[$(reboot)]', in ksh, [ "$OPTARG" -eq "$OPTARG" ] would return true (assuming $x is unset or not things like nan, RANDOM, ++y...) and... reboot. – Stéphane Chazelas Oct 29 '18 at 18:44
2

Another thing not pointed out here (but corrected in the code) is that you should never use shift inside the while getopts loop. getopts takes care of stepping through the arguments itself, and if you change the arg list out from under it, things will get very confused. Instead, wait 'till after the loop, and then run shift "$((OPTIND - 1))" to remove all options from the arg list at once. – Gordon Davisson Oct 29 '18 at 18:49
@GordonDavisson, exactly. With the shift 2 in the code for -d, something like -d 1 -d 2 -d 3 would result in the code only seeing -d 1 and -d 3, the -d 2 being shifted away in between. – ilkkachu Oct 29 '18 at 21:21
fwiw, dash seems to be the only shell that handles well (ie the way I naively expect it) the arg list being changed from underneath getopts (either with shift or with set -- ...). – Oct 31 '18 at 21:15

score 0 · Answer 2 · answered Oct 22 '18 at 19:58

The single square bracket [ is posix-compliant but harder to use than [[, which you can usually use in bash. Under the single-square-bracket standard, -eq is for integers only, not strings. For example, the following works fine: if [ "2" -eq "2" ] ; then echo foo; fi. You can either use double-square-brackets, for which -eq accepts strings, or use = and the single-square bracket form:

if [ "bar" = "bar" ] ; then echo foo; fi

Check out https://ryanstutorials.net/bash-scripting-tutorial/bash-if-statements.php for info on the POSIX if test and http://tldp.org/LDP/abs/html/testconstructs.html for info on different kinds of test constructs such as (( and [[.

Thanks fór answer! :) But that does not solve shifting problem. Could you please add answer to that too ? — Traabefi, Oct 22 '18 at 20:17

GETOPTS parse empty and nonempty args

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