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Re: Possible bug in getopts when required argument is not supplied

From: Dennis Williamson
Subject: Re: Possible bug in getopts when required argument is not supplied
Date: Fri, 13 Nov 2015 13:02:54 -0600

On Fri, Nov 13, 2015 at 10:13 AM, Griff Miller II <address@hidden> wrote:
Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: cygwin
Compiler: gcc
Compilation CFLAGS:  -DPROGRAM='bash.exe' -DCONF_HOSTTYPE='x86_64'
-DCONF_OSTYPE='cygwin' -DCONF_MACHTYPE='x86_64-unknown-cygwin'
-DCONF_VENDOR='unknown' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash'
-I/usr/src/bash-4.3.42-4.x86_64/src/bash-4.3/lib  -DWORDEXP_OPTION -ggdb
-O2 -pipe -Wimplicit-function-declaration
uname output: CYGWIN_NT-6.1 MILLERIG1 2.3.0(0.291/5/3) 2015-11-09 10:24
x86_64 Cygwin
Machine Type: x86_64-unknown-cygwin

Bash Version: 4.3
Patch Level: 42
Release Status: release

        getopts doesn't always detect that a required argument is not

        Here is a test script:


# Parse command-line options.
while getopts $opts opt ; do
        case $opt in
                        exit 1

echo a = \"${a}\"
echo b = \"${b}\"
echo c = $c

% ./myscript -a a
a = "a"
b = ""
c = 0
% ./myscript -a a -b
./test_bash_getopts_unsilent_reporting: option requires an argument -- b
% ./myscript -a a -b b
a = "a"
b = "b"
c = 0
% ./myscript -a -b b
a = "-b"
b = ""
c = 0

Note that in the last run, getopts does not detect that nothing was passed
via -a, even though -a requires it. Instead, it thinks the next switch
(-b) is the value of -a. Perhaps this was a conscious decision, so that
values starting with '-' can be passed, but it's a more of a surprise to
the developer than discovering that the user can't do e.g. ./myscript -a
-my_a_val .  Can this bug, if it's deemed a bug, be fixed, else the
manpage updated in the getopts section to make it clear what is going on?

If there is a requirement that the user be able to have optargs that start
with '-', maybe not allow OPTARG be one of the options in the first
argument to getopts ($opts in the above script)?

Thank you.

Your opts string needs to begin with a colon to enable silent error reporting and you need to handle the colon in your case statement as the condition where a required argument is missing.



  :) echo "Missing argument for option -$OPTARG" >&2;;

You should escape the question mark since otherwise it's a globbing character:

  \?) echo "Unknown option: -$OPTARG" >&2; exit 1;;

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