Expression evaluation in search and replace regex

JojoLinkyBob has asked for the wisdom of the Perl Monks concerning the following question:

Greetings council, I have a problem, which is probably just a trivia question to you guys:

This works:

my %fruitcolors = ( banana=>"yellow" );
$_ = "applebananachocolate";
s/apple(banana)chocolate/$fruitcolors{$1}/ie;
[download]

But this doesn't:

s/(apple)(banana)(chocolate)/$1$fruitcolors{$2}$3/ie;
[download]

Is there a special delimiter I need?

Thanks in advance

=~Desertcoder

Edit Masem 2002-01-21 - Changed title from "Expressionless :"

Comment on Expression evaluation in search and replace regex Select or Download Code

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Re: Expressionless : by japhy (Canon) on Jan 20, 2002 at 23:48 UTC
The `/e` modifier is not useful here. Remove it. That's what's giving you trouble. If you needed to execute code, then it would be useful. Not here. _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker. `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply]
Re: Expressionless : by belg4mit (Prior) on Jan 20, 2002 at 23:24 UTC
With /e the second half of s/// is an expression, you must manually concatenate your variables. The first works because there is no need to concatenate a single variable (to what?!). It's an easy enough mistake to make. UPDATE: Note I explicitly did not say use . because you only need effect a concatenation. TIMTWOTDI, you could also use an interpolating quote. `-- perl -pe "s/\b;([st])/'\1/mg"`	[reply]
Re: Re: Expressionless : by JojoLinkyBob (Scribe) on Jan 20, 2002 at 23:46 UTC
Doh! I should have known that. Thanks for your rapid response. =~Desertcoder	[reply]
Re: Expressionless : by blakem (Monsignor) on Jan 20, 2002 at 23:39 UTC
For this particular regex, you could rewrite it using a look-ahead and look-behind assertion.... `s/(?<=apple)(banana)(?=chocolate)/$fruitcolors{$1}/i;` [download] Seems a bit better than replacing pieces with identical copies of themselves..... Update: removed superfluous /e that japhy points out below -Blake	[reply] [d/l]
Re: Expressionless : by dws (Chancellor) on Jan 20, 2002 at 23:30 UTC
When asking for help on problems like this, it helps to also include the error message you're getting from Perl. The /e modifier says to treat the right-hand side of the substitution as an expression. But `$1$fruitcolors{$2}$3` isn't a valid Perl expression. To make it valid, add string concatenation operators, as follows: `s/(apple)(banana)(chocolate)/$1 . $fruitcolors{$2} . $3/ie;`	[reply] [d/l] [select]