Help in using two arrays

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

Hi all, I have imported the contents of two text files into two arrarys. Array 1 @file contains the following:

<tag>line one
line two
line three
<tag>line four
[download]

Array 2 @cmds contains the following:
\replace<tab>tag<tab>element<br>\replace<tab>it<tab>italic
I want to open the first array go through line by line and replace based on the conditions given on array 2. The output I desire should look like:

<element>line one
line two
line three
<element>line four
[download]

I tried using the following code:

foreach(@file)
{
    for my $x (0..$#replace)
    {
        if($replace[$x] =~ /\\replace\t(.+?)\t(.+?)\n/g)
        {
            $_ =~ s/$1/$2/g;
        }
    print $_;
    }
}
[download]

Can someone tell me where I am going wrong?

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Re: Help in using two arrays by ikegami (Patriarch) on Jun 11, 2008 at 14:10 UTC
Quickly, I might not have caught everything 'g' modifier in an `if` is almost always wrong. It is wrong here. `$2` in `s/.../$2/` refers to the second capture in `...`, not some earlier capture by some other match or substitution operator. The search expression appears to be text, not a regexe, but you use it as a regexp. Using `$_` in `$_ =~ s/$1/$2/g;` and `print $_;` defies the purpose of using `$_`. `for my $line (@lines) { for my $replace (@replaces) { my ($s,$r) = $replace =~ /\\replace\t(.+?)\t(.+?)\n/ or next; $line =~ s/\Q$s\E/$r/g; } print $line; }` [download] Update: Actually, that's a bad approach since you have to keep recompiling regexps. Reverse the nesting of your loops: `for my $replace (@replaces) { my ($s,$r) = $replace =~ /\\replace\t(.+?)\t(.+?)\n/ or next; s/\Q$s\E/$r/g for @lines; } print @lines;` [download] Update: Woops, I was still using $2. Switched to $r.	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: Help in using two arrays
by ikegami (Patriarch) on Jun 11, 2008 at 14:10 UTC

Quickly, I might not have caught everything

'g' modifier in an if is almost always wrong. It is wrong here.
$2 in s/.../$2/ refers to the second capture in ..., not some earlier capture by some other match or substitution operator.
The search expression appears to be text, not a regexe, but you use it as a regexp.
Using $_ in $_ =~ s/$1/$2/g; and print $_; defies the purpose of using $_.

for my $line (@lines)
{
    for my $replace (@replaces)
    {
        my ($s,$r) = $replace =~ /\\replace\t(.+?)\t(.+?)\n/
            or next;

        $line =~ s/\Q$s\E/$r/g;
    }

    print $line;
}
[download]

Update: Actually, that's a bad approach since you have to keep recompiling regexps. Reverse the nesting of your loops:

for my $replace (@replaces)
{
    my ($s,$r) = $replace =~ /\\replace\t(.+?)\t(.+?)\n/
        or next;

    s/\Q$s\E/$r/g for @lines;
}

print @lines;
[download]

Update: Woops, I was still using $2. Switched to $r.

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