This is a good question. The reason is that, on the regex side, the two character sequence "\n" is a metacharacter that means "match a literal newline".

After the value of $changefrom is interpolated, the regular expression engine compiles the regex, sees "\n", and compiles it to match a newline. (If $changeto instead contained a literal newline, the result would be the same, because a literal newline in a regex matches a literal newline.)

On the replacement side, however, once the value of $changeto is interpolated, there is no second pass over the string to turn "\n" into a newline.

One solution is to code the extra pass over $changeto yourself, as in: 

$changeto =~ s/\\n/\n/g;
$file_contents =~ s/$changefrom/$changeto/gi;

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Please note that that simple example will change \\n to \<newline>.

Of course, you then have to consider which escape sequences you want to allow. \t and \r? How about \040, \x20, or \cD? That's up to you. :)

In reply to Re: Re: Change utility; code optimization by chipmunk
in thread Change utility; code optimization by gryphon

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