Beginner am Freitag, 24. November 2006 14:48:
> Hi,
>
> 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'.
Hi Beginner
I assume that you mean "substitue with _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?
I should not mention that in the public ;-) but, just to demonstrate one way
to search for a reason for a malfunction:
Because I did not see an error at first glance, I...
> #!/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");
...replaced these two lines with simply
my @files=qw(DSC00092a.jpg DSC00094c.jpg); # etc
and everything worked fine.
Then, I created these files in the current directory, and again everything
worked fine.
Then, I made a subdirectory, moved the file over, ...
> foreach my $f (@files) {
> (my $l) = ($f =~ /([a-z]|[a-z][a-z])\.jpg/);
> (my $new = $f) =~ s/$l/_a/;
...placed here a
warn "new=$new";
and got (excerpt):
new=/home/d_ani/ramsch/thumbs/DSC00092a.jpg at ./script.pl line 17. # !!
new=/home/dani/ramsch/thum_as/DSC00093b.jpg at ./script.pl line 17. # !!
new=/home/dani/rams_ah/thumbs/DSC00094c.jpg at ./script.pl line 17. # !!
new=/home/dan_a/ramsch/thumbs/DSC00100i.jpg at ./script.pl line 17. # !!
new=/home/dani/ramsch/thumbs/DSC00101_a.jpg at ./script.pl line 17.
> my $basef = basename($f);
> my $basenew = basename($new);
> print "$basef -> $basenew $l\n";
> }
And now it's extraordinary obvious that the error is
(my $new = $f) =~ s/$l/_a/;
which simply searches for the first char contained in $l and replaces it
with '_a'. This makes the malfunction dependent from the contents in $dir.
Instead, this line should be more specific, f.ex:
(my $new = $f) =~ s/$l\.jpg$/_a\.jpg/;
(Note that I anchor with $ since "DSC00092a.jpg" is a valid path name :-) )
Of course it would have been sufficient to only present this last substitution
to lead you to a "aha!", but I think it's important to have a personal
strategy to search for errors in the dark :-)
btw, the foreach code can at least be shortened to:
foreach my $basef (map basename ($_), @files) {
(my $l) = ($basef =~ /([a-z]{1,2})\.jpg$/);
# above line is still problematic: What if the match failes?
(my $basenew = $basef) =~ s/$l\.jpg$/_a\.jpg/;
print "$basef -> $basenew $l\n";
}
and certainly optimized further in several ways (f.ex if you don't need the
last print statement, $l could possibly be eliminated), but I'm so tired and
brain dead at the time :-)
Dani
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