NAME¶
File::GlobMapper - Extend File Glob to Allow Input and Output Files
SYNOPSIS¶
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 ;
DESCRIPTION¶
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.
Behind The Scenes¶
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.
Limitations¶
"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
- 1.
- No nested {}
- 2.
- Whitespace does not delimit fileglobs.
- 3.
- The use of parenthesis can be used to capture parts of the input
filename.
- 4.
- If an Input glob matches the same file more than once, only the first will
be used.
The syntax
- ~
- ~user
- .
- 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
[^/]?
- \
- Backslash is used, as usual, to escape the next character.
- []
- Character class.
- {,}
- Alternation
- ()
- Capturing parenthesis that work just like perl
Any other character it taken literally.
Output File Glob¶
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
- "*"
- The "*" character will be replaced with the complete input
filename.
- #1
- Patterns of the form /#\d/ will be replaced with the
Returned Data¶
EXAMPLES¶
A Rename script¶
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'
A few example globmaps¶
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>'
SEE ALSO¶
File::Glob
AUTHOR¶
The
File::GlobMapper module was written by Paul Marquess,
pmqs@cpan.org.
COPYRIGHT AND LICENSE¶
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.