CODEWITHSUNDEEP
shellksh
voltas
voltas

Reputation: 563

Korn script parameters

I have came across a below code snippet and not sure exactly what's the purpose of -? in the while loop. I searched across multiple sites and forums for this parameter but couldn't get any exact answer.

Any inputs please, thank you.

while [[ $1 = -? ]]; do 
   case $1 in 
    -a) a1=alligator ;; 
    -b) a2=bear ;; 
    -c) a3=cougar ;; 
   esac 
   shift

Upvotes: 0

Views: 39

Answers (1)

glenn jackman
glenn jackman

Reputation: 246774

In ksh, within double brackets, the = and == operators are for pattern matching: [[ string = pattern ]] [1]

These are shell pathname expansion patterns. ? will match any single character.

So what you're testing for is if $1 matches a hyphen followed by any single character. In other words, does the first positional parameter look like an option string.

[1] -- to perform string equality checking, your pattern either contains no special globbing characters, or such characters are quoted or escaped.

IMO, a more robust way to do option parsing is with the getopts builtin:

while getopts :abc opt; do
    case $opt in
        a) a1=alligator ;; 
        b) a2=bear ;; 
        c) a3=cougar ;; 
        :) print -u2 "error: missing required argument for -$OPTARG" ;;
        ?) print -u2 "unknown option: -$OPTARG" ;;
    esac
done
shift $((OPTIND - 1))

Upvotes: 2

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