Re: Regular Expression Help?

On Tuesday, November 4, 2003, at 04:47 PM, David Fetter wrote:

> On Tue, Nov 04, 2003 at 04:35:45PM -0800, Josh Berkus wrote:
>> Currently, I'm doing 3
>> substitutions, along the lines of:
>
>> $eline =~ s/#NAME/$ename/g;
>>
>> But that's not very sophisticated and I'd like to improve my use of
>> regexp. Suggestions?

It's not always the case that a single regex is more efficient or
elegant than multiple regexen. For example, when I want to strip
whitespace from the beginning _and_ end of a string, this:

s/^\s+//;
s/\s+$//;

Is faster than:

s/^\s+|\s+$//g;

Or so I have read.

> IMHO, your current system may be easier to maintain than this:
>
> %replacements = (
> '#NAME' => $ename
> , '#DATE' => $mdate
> , '#DETAIL' => $edetail
> );
>
> $eline =~ s/(#NAME|#DATE|#DETAIL)/$replacements{$1}/g;
>
> Or it may not. Anyhow, that's the way I'd set it up if I were
> changing it :)

This is probably how I would do it, too, though perhaps like this:

> $eline =~ s/(#\w+)/$replacements{$1} || $1/ge;

But it's possible that it's not any faster, because it has to do a hash
lookup for each replacement. I would benchmark this against what you
have. Of course, if what you need to maintain could change the # lines
now and then, it's easiest to just edit a hash, rather than write more
regexen.

HTH,

David

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