I know that a single dash goes with one character when we set options using getopt or optparse. but is there anyway to use a single dash with more than one character, like -apply?
I know that a single dash refers to a short name, and conventionally people use one character for it. but there are some commands (eg, find -printf) that use long name with a single dash.
Does anyone know how to use long name with a single dash in bash on Linux (using getopt or optparse other bash tools)?
From getopt's manpage:
-a, --alternative
Allow long options to start with a single '-'.
Or, if we're talking about the getopt* C functions:
getopt_long_only() is like getopt_long(), but '-' as well as "--" can indicate a long option
getopts or equivalent functions in pretty much all programming languages and they don't al behave the same way.
– terdon
Aug 24 '16 at 14:05
If you have a GNU system, and want single-dash long options, then by all means use getopt_long or getopt -a.
The example of find -printf was what lead me to note about the GNU extensions: The one-dash options for find exist outside GNU systems too, and the heritage is likely much older than that of the GNU-style long options. So programs like find probably don't use getopt_long, but just parse their command line options by hand. In bash, it might look something like this:
$ cat args.sh
#!/bin/sh
foo=0
bar=0
while [ "$#" -ne 0 ] ; do
if [ "$1" = "-foo" ] ; then
foo=1
elif [ "$1" = "-bar" ] ; then
shift
bar=$1
fi
shift
done
echo foo: "$foo"
echo bar: "$bar"
$ ./args.sh -bar x -foo
foo: 1
bar: x
The difficulty with parsing single-character option is that they can be bundled (e.g. -ab is equivalent to -a -b). GNU-style long options have the difficulty that arguments can be joined or not. With single-dash multi-character options, there isn't any parsing difficulty so you can easily do it by hand.
Most programs with single-dash multi-character options take arguments in a separate command line argument.
foo=
bar=default
require_argument () {
if [ $# -eq 2 ]; then
echo >&2 "$0: Option $1 requires an argument"
exit 2
fi
eval "$1=\"\$3\""
}
while case "$1" in
--) shift; false;;
-foo) foo=1
-bar) require_argument bar "$@"; shift;;
-?*) echo >&2 "$0: Unknown option $1"; exit 2;;
*) false;;
esac
do
shift
done
Do consider using GNU-style long options. They have more standardized behavior and more people are familiar with them.
cp,ls,psandtar) accept long names with single hyphens (so you can saycp -archive -dereference -recursivein your shell scripts), or is it about writing new programs to accept a find-like syntax (which will create a painful user experience, because it’s a non-standard user interface that is incompatible with 95% of the system)? – G-Man Says 'Reinstate Monica' Aug 25 '16 at 04:29if (strcmp(argv[1],"-foo") == 0) …. (If you have more than a few options, you should put them in an array:strcmp(argv[1],myopts[i]) ….) – G-Man Says 'Reinstate Monica' Aug 26 '16 at 07:44