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

I'm trying to get a string from a regexp, then pass it to a function I made, to remove special symbols from it and save it (to a file, for example). If that inital string comes with a "\" somewhere whitin, after I pass it trought the function, it disappears. I don't want that. Here is how I do it: 
if ($line =~ /blablabla :(.+?): bleblable/){
$my_var = fixn($1);
do_whatever_I_want_with($my_var);
}

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Here is the function: 
sub fixn($){
        my $str = "@_";
        $str =~ s/[^a-zA-Z0-9^_\-\\`\.\[\]\{\}~]//g;
        chomp $str;
        return $str;
}

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I have the feeling, that backslashes are lost in my $str = "@_"; <= that quotes turn them into a escape sequences.
Any idea how to keep the backslashes?

Replies are listed 'Best First'.
Re: Problem with interpolating backslash
by Joost (Canon) on Aug 20, 2005 at 12:22 UTC
    Please do not use prototypes if you don't know why they are problematic. Search for prototypes for more info. 

    #!/usr/bin/perl -w
use strict;

sub fixn($) {
    my $str = "@_";
    $str =~ s/[^a-zA-Z0-9^_\-\\`\.\[\]\{\}~]//g;
    return $str;
}

sub fixn2 {          # no prototype needed
    my $str = shift; # since we only ever want 1 argument
                     # which will be converted to a string
                     # if needed anyway.
    $str =~ s/[^a-zA-Z0-9^_\-\\`\.\[\]\{\}~]//g;
    return $str;
}

my $input = 'a b \\ c d';
print "input='$input'\n";
my $myvar = fixn($input);
print "myvar='$myvar'\n";
my $better = fixn2($input);
print "better='$better'\n";

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    output: 
    input='a b \ c d'
myvar='ab\cd'
better='ab\cd'

    [download]

    In other words, your regex is fine, but your code is sloppy, and your problem is probably somewhere in do_whatever_I_want_with()

    update:

    I have the feeling, that backslashes are lost in my $str = "@_"; <= that quotes turn them into a escape sequences.

    That doesn't happen: backslashes are only interpreted in literal strings, they are not "recursively" interpreted in interpolated variables. The only exception is when you embed a variable in a regex, like so: 

     $var = "bla[abc]\\t";  # $var contains bla[abc]\t
 /$var/;      # is equivalent to /bla[abc]\t/
 /\Q$var\E/;  # is equivalent to /bla\[abc\]\\t/

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    "What should it profit a man, if he should win a flame war, yet lose his cool?"
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      "Please do not use prototypes if you don't know why they are problematic."

      Also ;-), please do not use prototypes if you know why they are problematic. It is generally a bad idea to use Perl prototype.

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        I solved the problem :)
        Instead  my $str = "@_"; I used  my $str = $_[0]; which is the same as shift.
        Interesting ideas, I'll meditate on them :)
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[d/l]
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Re: Problem with interpolating backslash
by davido (Cardinal) on Aug 20, 2005 at 15:56 UTC
[reply]

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