How to pass a long option to a bash script? - bash

Question

./script.sh -abc hello
How can I write my script to use '-abc' as the option and 'hello' as the value to that option?
I should be able to pass this value to all the functions in this script. Lets say I have 2 functions: X and Y.

Answer 1

Use this in your script:
[[ $1 == -abc ]] && value="$2" || echo invalid option
If you don't want to print any messages on wrong option or no option, then omit the || echo ... part, value will be empty.
If you want to make the second argument a must, then:
[[ $1 == -abc ]] && [[ $2 != "" ]] && value="$2" || echo invalid option
Using if else loop will give you complete control over this:
if [[ $1 == -abc ]]; then
#if first option is valid then do something here
if [[ $2 != "" ]]; then
value="$2"
else
#if second option is not given then do something here
echo invalid option
fi
else
echo invalid option
#if first option is invalid then do something here
fi
If you want to make the first argument a must too, then change the first if statement line to
if [[ $1 == -abc && $1 != "" ]]; then
If you want to pass as many arguments as you wish and process them,
then use something like this:
#!/bin/bash
opts=( "$#" )
#if no argument is passed this for loop will be skipped
for ((i=0;i<$#;i++));do
case "${opts[$i]}" in
-abc)
# "${opts[$((i+1))]}" is the immediately follwing option
[[ "${opts[$((i+1))]}" != "" ]] &&
value="${opts[$((i+1))]}"
echo "$value"
((i++))
#skips the nex adjacent argument as it is already taken
;;
-h)
#dummy help option
echo "Options are [-abc value], -h"
;;
*)
#other unknown options
echo invalid option
break
;;
esac
done
This is an example of handling multiple arguments with only two options available -abc value and -h

Answer 2

bash doesn't have a built in command for processing long arguments. In order to parse long options in a shell script, you'll need to iterate over the arguments list yourself.
Here's one approach:
#!/bin/sh
is_option_arg () {
case $1 in
-*)
return 1
;;
*)
return 0
;;
esac
}
usage () {
echo "$(basename "$0") -abc ARG -def ARG -verbose"
}
OPT_ABC=
OPT_DEF=
OPT_VERBOSE=false
while [ "$#" -gt 0 ]; do
case $1 in
-abc)
shift
{ [ "$#" -ne 0 ] && is_option_arg "$1"; } || { usage >&2; exit 1; }
OPT_ABC=$1
;;
-def)
shift
{ [ "$#" -ne 0 ] && is_option_arg "$1"; } || { usage >&2; exit 1; }
OPT_DEF=$1
;;
-verbose)
OPT_VERBOSE=true
;;
*)
break
;;
esac
shift
done
echo "OPT_ABC=$OPT_ABC"
echo "OPT_DEF=$OPT_DEF"
echo "OPT_VERBOSE=$OPT_VERBOSE"
if [ "$#" -gt 0 ]; then
echo "Remaining args:"
for arg in "$#"; do
echo "$arg"
done
fi

Answer 3

You pretty much have to implement it yourself manually. Here's one way:
abc=
while [[ "$1" == -* ]]; do
opt=$1
shift
case "$opt" in
-abc)
if (( ! $# )); then
echo >&2 "$0: option $opt requires an argument."
exit 1
fi
abc="$1"
shift
;;
*)
echo >&2 "$0: unrecognized option $opt."
exit 2
;;
esac
done
echo "abc is '$abc', remaining args: $*"
Some sample runs of the above:
(0)$ ./script.sh
abc is '', remaining args:
(0)$ ./script.sh hello
abc is '', remaining args: hello
(0)$ ./script.sh -abc hello
abc is 'hello', remaining args:
(0)$ ./script.sh -abc hello there
abc is 'hello', remaining args: there
(0)$ ./script.sh -abc
./script.sh: option -abc requires an argument.
(1)$ ./script.sh -bcd
./script.sh: unrecognized option -bcd.
(2)$