Re: failed substitution

Beginner wrote:
Hi,

Hello,

I have a number of jpegs I wanted to rename. I wrote a short script
to do it but the new file name is not always generated correctly. The
script should find the last letter in the filename (before the
extension) and substitute it for '_a'.

If you look at the results below you'll see that 'a' and 'b' fail but
'c' worked. I don't understand why.

DSC00092a.jpg -> DSC00092a.jpg a
DSC00093b.jpg -> DSC00093b.jpg b
DSC00094c.jpg -> DSC00094_a.jpg c
DSC00095d.jpg -> DSC00095d.jpg d
DSC00096e.jpg -> DSC00096e.jpg e
DSC00097f.jpg -> DSC00097f.jpg f
DSC00098g.jpg -> DSC00098g.jpg g
DSC00099h.jpg -> DSC00099h.jpg h
DSC00100i.jpg -> DSC00100i.jpg i
DSC00101j.jpg -> DSC00101_a.jpg j
DSC00102k.jpg -> DSC00102_a.jpg k
DSC00103l.jpg -> DSC00103l.jpg l
...snip

Here the script, there isn't much to it. Can anyone explain why the
substitute fails?


#!/bin/perl
# Active State 5.8.6.811

use strict;
use warnings;
use File::Basename;

my $dir = 'D:/Temp/jpegs/thumbs/';
my @files = glob("${dir}*.jpg");

foreach my $f (@files) {
(my $l) = ($f =~ /([a-z]|[a-z][a-z])\.jpg/);

Perl's alternation always quits when the first alternative matches so in your
example ([a-z]) and ([a-z]|[a-z][a-z]) are equivalent. Perhaps you meant
([a-z]{1,2}) instead?


(my $new = $f) =~ s/$l/_a/;

$f contains the complete path so you are probably modifying something other
than the file name.

You probably want something like:

( my $new = $f ) =~ s/([a-z]{1,2})(?=\.jpg\z)/_a/;


my $basef = basename($f);
my $basenew = basename($new);
print "$basef -> $basenew $l\n";
}


John
--
Perl isn't a toolbox, but a small machine shop where you can special-order
certain sorts of tools at low cost and in short order. -- Larry Wall
.

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