Escaping confusion in RE...

freddo411 has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

I'm trying to do a "simple" find and replace.
I'm looking for L:\Data\5555\
to replace with D:\Sites\5555\Data\

I also want to generalize the numeric part. So I tried this RE:


s#l:\\Data\\([0-9]*)\\#D:\\Sites\\$1\Data\\#i;
[download]

This has strange effects causing an infinite loop during my replace. The backslash character is causing me trouble.

I am not using these paths, just replacing them as text in a file.

Thanks in advance for your advice.

-------------------------------------
Nothing is too wonderful to be true
-- Michael Faraday

Comment on Escaping confusion in RE... Download Code

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Re: Escaping confusion in RE... by Joost (Canon) on Jul 05, 2007 at 22:21 UTC
You're missing an \\ escape at $1\Data. Try: `use warnings; use strict; my $a = 'L:\\Data\\5555\\'; $a =~ s#l:\\Data\\([0-9])\\#D:\\Sites\\$1\\Data\\#i; print $a;` [download] recent perls with warnings and strict enabled would have given you a warning: `Unrecognized escape \D passed through at FILENAME line NUMBER.` [download] "What should it profit a man, if he should win a flame war, yet lose his cool?"*	[reply] [d/l] [select]
Re: Escaping confusion in RE... by runrig (Abbot) on Jul 05, 2007 at 22:25 UTC
What makes you think there is an infinite loop? BTW, you only have one backslash before 'Data' on the RHS in your example. Other than that, you seem to have it correct, by just doubling up on all the backslashes.	[reply]
Re^2: Escaping confusion in RE... by freddo411 (Chaplain) on Jul 05, 2007 at 22:36 UTC
I didn't give enough context. My bad. The substitution does seem to work. Here's more context, and the error. `while ( @file ) { s#l:\\Data\\([0-9]*)\\#D:\\Sites\\$1\\Data\\#i; print; }` [download] @file is filled with many lines like so: my @file = <FILE>; Here are the warnings: `Use of uninitialized value in print at foo.pl line 44. Use of uninitialized value in substitution (s///) at foo.pl line 43. Use of uninitialized value in substitution (s///) at foo.pl line 43.` [download] ------------------------------------- Nothing is too wonderful to be true -- Michael Faraday	[reply] [d/l] [select]
Re^3: Escaping confusion in RE... by runrig (Abbot) on Jul 05, 2007 at 22:40 UTC
If @file is an array then you want a for loop, not a while loop. If you want to read lines from a file into `$_` then you want `while ( <FILE> ) {` I.e., you do have an infinite loop, @file has a constant number of things in it, so it is always true, unless you shift or pop things from it in the loop. (but a for loop is probably more appropriate).	[reply] [d/l] [select]
Re^3:Escaping confusion in RE... by toolic (Bishop) on Jul 06, 2007 at 00:36 UTC
`([0-9]*)` will match zero or more digits. To be a little cleaner, you probably should match 1 or more digits using `([0-9]+)`	[reply] [d/l] [select]