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Wed, 12 Nov 2008

Flag variables in Bourne shell programs
Who the heck still programs in Bourne shell? Old farts like me, occasionally. Of course, almost every time I do I ask myself why I didn't write it in Perl. Well, maybe this will be of some value to some fart even older than me..

Suppose you want to set a flag variable, and then later you want to test it. You probably do something like this:

        if some condition; then
            IS_NAKED=1
        fi

        ...

        if [ "$IS_NAKED" == "1" ]; then
          flag is set
        else
          flag is not set
        fi
Or maybe you use ${IS_NAKED:-0} or some such instead of "$IN_NAKED". Whatever.

Today I invented a different technique. Try this on instead:

        IS_NAKED=false
        if some condition; then
            IS_NAKED=true
        fi

        ...

        if $IS_NAKED; then
          flag is set
        else
          flag is not set
        fi
The arguments both for and against it seem to be obvious, so I won't make them.

I have never seen this done before, but, as I concluded and R.J.B. Signes independently agreed, it is obvious once you see it.

[ Addendum 20090107: some followup notes ]


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