File::GlobMapper - Extend File Glob to Allow Input and Output Files
use File::GlobMapper qw( globmap );
my $aref = globmap $input => $output
or die $File::GlobMapper::Error ;
my $gm = new File::GlobMapper $input => $output
or die $File::GlobMapper::Error ;
This module needs Perl5.005 or better.
This module takes the existing File::Glob module as a starting point and
extends it to allow new filenames to be derived from the files matched by
File::Glob.
This can be useful when carrying out batch operations on multiple files that have both an input filename and output filename and the output file can be derived from the input filename. Examples of operations where this can be useful include, file renaming, file copying and file compression.
To help explain what File::GlobMapper does, consider what code you
would write if you wanted to rename all files in the current directory
that ended in .tar.gz to .tgz. So say these files are in the
current directory
alpha.tar.gz
beta.tar.gz
gamma.tar.gz
and they need renamed to this
alpha.tgz
beta.tgz
gamma.tgz
Below is a possible implementation of a script to carry out the rename (error cases have been omitted)
foreach my $old ( glob "*.tar.gz" )
{
my $new = $old;
$new =~ s#(.*)\.tar\.gz$#$1.tgz# ;
rename $old => $new
or die "Cannot rename '$old' to '$new': $!\n;
}
Notice that a file glob pattern *.tar.gz was used to match the
.tar.gz files, then a fairly similar regular expression was used in
the substitute to allow the new filename to be created.
Given that the file glob is just a cut-down regular expression and that it has already done a lot of the hard work in pattern matching the filenames, wouldn't it be handy to be able to use the patterns in the fileglob to drive the new filename?
Well, that's exactly what File::GlobMapper does.
Here is same snippet of code rewritten using globmap
for my $pair (globmap '<*.tar.gz>' => '<#1.tgz>' )
{
my ($from, $to) = @$pair;
rename $from => $to
or die "Cannot rename '$old' to '$new': $!\n;
}
So how does it work?
Behind the scenes the globmap function does a combination of a
file glob to match existing filenames followed by a substitute
to create the new filenames.
Notice how both parameters to globmap are strings that are delimited by <>.
This is done to make them look more like file globs - it is just syntactic
sugar, but it can be handy when you want the strings to be visually
distinctive. The enclosing <> are optional, so you don't have to use them - in
fact the first thing globmap will do is remove these delimiters if they are
present.
The first parameter to globmap, *.tar.gz, is an Input File Glob.
Once the enclosing "< ... >" is removed, this is passed (more or
less) unchanged to File::Glob to carry out a file match.
Next the fileglob *.tar.gz is transformed behind the scenes into a
full Perl regular expression, with the additional step of wrapping each
transformed wildcard metacharacter sequence in parenthesis.
In this case the input fileglob *.tar.gz will be transformed into
this Perl regular expression
([^/]*)\.tar\.gz
Wrapping with parenthesis allows the wildcard parts of the Input File
Glob to be referenced by the second parameter to globmap, #1.tgz,
the Output File Glob. This parameter operates just like the replacement
part of a substitute command. The difference is that the #1 syntax
is used to reference sub-patterns matched in the input fileglob, rather
than the $1 syntax that is used with perl regular expressions. In
this case #1 is used to refer to the text matched by the * in the
Input File Glob. This makes it easier to use this module where the
parameters to globmap are typed at the command line.
The final step involves passing each filename matched by the *.tar.gz
file glob through the derived Perl regular expression in turn and
expanding the output fileglob using it.
The end result of all this is a list of pairs of filenames. By default
that is what is returned by globmap. In this example the data structure
returned will look like this
( ['alpha.tar.gz' => 'alpha.tgz'],
['beta.tar.gz' => 'beta.tgz' ],
['gamma.tar.gz' => 'gamma.tgz']
)
Each pair is an array reference with two elements - namely the from
filename, that File::Glob has matched, and a to filename that is
derived from the from filename.
File::GlobMapper has been kept simple deliberately, so it isn't intended to
solve all filename mapping operations. Under the hood File::Glob (or for
older versions of Perl, File::BSDGlob) is used to match the files, so you
will never have the flexibility of full Perl regular expression.
The syntax for an Input FileGlob is identical to File::Glob, except
for the following
The syntax
Matches a literal '.'. Equivalent to the Perl regular expression
\.
Matches zero or more characters, except '/'. Equivalent to the Perl regular expression
[^/]*
Matches zero or one character, except '/'. Equivalent to the Perl regular expression
[^/]?
Any other character it taken literally.
The Output File Glob is a normal string, with 2 glob-like features.
The first is the '*' metacharacter. This will be replaced by the complete filename matched by the input file glob. So
*.c *.Z
The second is
Output FileGlobs take the
Below is a simple "rename" script that uses globmap to determine the
source and destination filenames.
use File::GlobMapper qw(globmap) ;
use File::Copy;
die "rename: Usage rename 'from' 'to'\n"
unless @ARGV == 2 ;
my $fromGlob = shift @ARGV;
my $toGlob = shift @ARGV;
my $pairs = globmap($fromGlob, $toGlob)
or die $File::GlobMapper::Error;
for my $pair (@$pairs)
{
my ($from, $to) = @$pair;
move $from => $to ;
}
Here is an example that renames all c files to cpp.
$ rename '*.c' '#1.cpp'
Below are a few examples of globmaps
To copy all your .c file to a backup directory
'</my/home/*.c>' '</my/backup/#1.c>'
If you want to compress all
'</my/home/*.[ch]>' '<*.gz>'
To uncompress
'</my/home/*.[ch].gz>' '</my/home/#1.#2>'
The File::GlobMapper module was written by Paul Marquess, pmqs@cpan.org.
Copyright (c) 2005 Paul Marquess. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.