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9.9. Renaming Files

9.9.1. Problem

You have many files whose names you want
to change.

9.9.2. Solution

Use a
foreach loop and the rename
function:

foreach $file (@NAMES) {
my $newname = $file;
# change $newname
rename($file, $newname) or  
warn "Couldn't rename $file to $newname: $!\n";
}

9.9.3. Discussion

This is straightforward. rename takes two
arguments. The first is the filename to change, and the second is its
new name. Perl's rename is a frontend to the
operating system's rename syscall, which typically won't rename files
across filesystem boundaries.

A
small change turns this into a generic rename
script, such as the one by Larry Wall shown in Example 9-5.

Example 9-5. rename

  #!/usr/bin/perl -w
# rename - Larry's filename fixer
$op = shift or die "Usage: rename expr [files]\n";
chomp(@ARGV = <STDIN>) unless @ARGV;
for (@ARGV) {
$was = $_;
eval $op;
die $@ if $@;
rename($was,$_) unless $was eq $_;
}

This script's first argument is Perl code that alters the filename
(stored in $_) to reflect how you want the file
renamed. It can do this because it uses an eval to
do the hard work. It also skips rename calls when
the filename is untouched. This lets you simply use wildcards like
rename EXPR
* instead of making long lists of filenames.

Here are five examples of calling the rename
program from the shell:

% rename 's/\.orig$//'  *.orig
% rename "tr/A-Z/a-z/ unless /^Make/"  *
% rename '$_ .= ".bad"'  *.f
% rename 'print "$_: "; s/foo/bar/ if <STDIN> =~ /^y/i'  *
% find /tmp -name "*~" -print | rename 's/^(.+)~$/.#$1/'

The first shell command removes a trailing ".orig"
from each filename.

The second converts uppercase to lowercase. Because a translation is
used rather than the lc function, this conversion
won't be locale-aware. To fix that, you'd have to write:

% rename 'use locale; $_ = lc($_) unless /^Make/' *

The third appends ".bad" to each Fortran file
ending in ".f", something many of us have wanted
to do for a long time.

The fourth prompts the user for the change. Each file's name is
printed to standard output and a response read from standard input.
If the user types something starting with a "y" or
"Y", any "foo" in the filename
is changed to "bar".

The fifth uses find to locate files in
/tmp that end with a tilde. It renames these so
that instead of ending with a tilde, they start with a dot and a
pound sign. In effect, this switches between two common conventions
for backup files.

The rename script exemplifies the powerful Unix
tool-and-filter philosophy. Even though we could have created a
dedicated command for lowercase conversion, it's nearly as easy to
write a flexible, reusable tool by embedding an
eval. By reading filenames from standard input, we
don't have to build in the recursive directory walk. Instead, we just
use find, which performs this function well.
There's no reason to recreate the wheel, although using File::Find we
could have.

9.9.4. See Also

The rename function in
perlfunc(1) and in Chapter 29 of
Programming Perl; your system's
mv(1) and rename(2)
manpages; the documentation for the standard File::Find module (also
in Chapter 32 of Programming Perl)