easy one for perl experts

[tas]

Ok, excuse me for being lazy, I could try and chase it down in tutorials, but maybe one of the gurus will just smile and know what has to be done: I want to tell perl to make a set of substitutions within a text file but ONLY for chunks of text that are inside curly brackets like so:

blah{arrglbarrgl}

These brackets appear randomly (i.e. not at beginning of lines). I want all other text to be left alone, but within the brackets every "X" replace by a "Y". I figure it must be the "lookahead expression," but how do I use it? Thanks guys!!!

[hayne]

There likely is a better way but I think the following should work as long as there is only one X inside each {}:

s/({[^}]*)X([^}]*})/$1Y$2/g

Explanation:
{[^}]* matches { followed by any number of non-} characters
[^}]*} matches any number of non-} characters followed by }
Putting these patterns in parentheses () captures the text into $1 and $2

[tas]

hayne,
thanks, that works! But (you guessed it) there's more than one "X" to replace in every string. But that was a nice solution, I should have thought of that myself!

[pmccann]

we got ugly...

#!/usr/bin/perl -w
use strict;
my $text="Something once out {in brackets more than once, more than once}
and {once more with once feeling} once again";
$text=~s/{(.*)}/$a=$1;$a=~s|once|twice|g;"{$a}"/eg;
print "$text\n";

Replace and rejig as required, but the essence is in there. Neater solutions welcome, this is a quick hack! Yep that's a substitution operator in a substitution slot. Ain't that cute?

Cheers,
Paul

[hayne]

Paul:
Don't you need that
{(.*)}
to be
{([^}]*}
in order to deal with the case where you have two (or more) braced enclosures on one line.
E.g.:
Like {this one case} within {this one line} of text
?

[tas]

YESYESYES! It works and does exactly what I need! Thanks Paul, it's so wonderful to have you around here. My next project: understanding how this works (so @ hayne: it seems to do multiple substitutions even w/o your editing). But don't post the solution yet, let me try and figure it out myself. And: THANKS MAN!

[tas]

I think I understood how the script works (great, this subsitution within a substitution!). There was indeed a problem when I had more than one pair of {} on a line: the "greedy" regexp would jump to the last one and substitute everything in between. So I came up with this solution, which does seem to be working:

 $_ =~ s/({)(.+?)(})/$a=$2;$a=~tr|X|Y|;"{$a}"/eg;

How do you like it?

[pmccann]

Sorry, I really was asleep when I wrote that one! hayne is spot on. It should certainly be a non-greedy quantifier (.*? or .+? will both be OK) in my first version in order to stop the problem with multiple brackets in the same chunk. Goes to show that I needed a better test string! hayne's proposed solution will also work fine...

Anyway, the following shows it working OK:

#!/usr/bin/perl -w
use strict;
my $text="Something once out {once, more than once} once {once}
and once more {once more with once feeling} once again";
$text=~s/{(.*?)}/$a=$1;$a=~s|once|twice|g;"{$a}"/eg;
print "$text\n"

As for your version, Tas: looks cool, but you can ditch those brackets around the braces and change the $2 back to $1. The use of "tr" is good for simple situations: I had interpreted your "X" and "Y" as placeholders, not what you were literally trying to replace!

Cheers,
Paul