Question

I am trying to replace every occurrence of “EXECUTE func-name” with “# EXECUTE func-name. followed by a hash value” ONLY if the func-name exists. My regex below doesn’t seem to agree with me.

s/EXECUTE ([\w-]+)\.?/"#  EXECUTE $1.\n" . $hash{$1}/eg if (exists($hash{$1}));

Please advise.

Answer 1

Well your code executes the if-condition before the actual regex, so you probably get a warning when executing your code.

When using the e-modifier you can use perl-code in the “replacement-part” directly:

s/EXECUTE\s+([\w-]+)\.?/
    if(exists($hash{$1})) {
        "#  EXECUTE $1.\n" . $hash{$1}
    } else {
        $&
    }/xeg;

I have added /x, so you can format the regexp to make it actually readable – but now you have to match the whitespace explicitly (that’s why I’ve added \s+ between EXECUTE and the group). The $& represents the whole match (so if there is no hash-entry for $1, nothing is changed).

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That said, using $& slows down every match and substitution without captures in your entire program. Here’s an improvement:

s/(EXECUTE\s+([\w-]+)\.?)/
    if(exists($hash{$2})) {
        "#  EXECUTE $2.\n" . $hash{$2}
    } else {
        $1
    }/xeg;