bash,sh,variable-assignment,short-circuiting , sh boolean short circuit variable assignment


sh boolean short circuit variable assignment

Question:

Tag: bash,sh,variable-assignment,short-circuiting

I'm trying to write a script that takes flags as parameters, so I want to be able to handle them being passed in any order.

This is what I have so far:

#!/bin/sh    

numargs=$#
echo $numargs

check_param () {
    if [ "$1" = "$2" ]; then
        return 1
    else
        return 0
    fi
}

S=0
T=0
for ((i=1 ; i <= numargs ; i++)); do
    S=$S || check_param $1 "-s"
    T=$T || check_param $1 "-t"
    shift
done

echo "$S"
echo "$T"

however even though the function is returning 1 when the parameters are set, the variable / short circuit assignment doesn't seem to work.

$ ./script.sh aa ddd fff -s rrr
5
0
0
$ ./script.sh aa ddd fff -s rrr -t
6
0
0

Answer:

I guess you're trying to do this:

#!/bin/sh    

S=0
T=0

numargs=$#
printf "You passed %s arguments\n" "$numargs"

check_param () {
    if [ "$1" = "$2" ]; then
        return 1
    else
        return 0
    fi
}

i=1
while [ "$i" -le "$numargs" ]; do
   current_arg=$1
   shift
   case $current_arg in
      (-s)
         S=1 ;;
      (-t)
         T=1 ;;
      (*)
         set -- "[email protected]" "$current_arg" ;;
   esac
   i=$((i+1))
done

printf "S flag: %s\n" "$S"
printf "T flag: %s\n" "$T"

if [ $# = 0 ]; then
   printf "No arguments left.\n"
else
   printf "Arguments left (%s):\n" "$#"
   printf "   %s\n" "[email protected]"
fi

I called this script banana, chmod +x banana and:

$ ./banana
You passed 0 arguments
S flag: 0
T flag: 0
No arguments left.
$ ./banana one two -s three
You passed 4 arguments
S flag: 1
T flag: 0
Arguments left (3):
   one
   two
   three

This will tell you whether an -s or -t option is given, and will leave the arguments on the arguments stack!


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