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9.6. Globbing, or Getting a List of Filenames Matching a Pattern
9.6.1. Problem
You want to get a list of filenames
similar to those produced by MS-DOS's *.* and
Unix's *.h. This is called
globbing, and the filename wildcard expression
is called a glob, or occasionally a
fileglob to distinguish it from a
typeglob.
9.6.2. Solution
Perl provides globbing with the semantics of the Unix C shell through
the glob keyword and
<>:
@list = <*.c>;
@list = glob("*.c");
You can also use readdir to extract the filenames
manually:opendir(DIR, $path);
@files = grep { /\.c$/ } readdir(DIR);
closedir(DIR);
9.6.3. Discussion
In versions of Perl before v5.6, Perl's built-in
glob and <WILDCARD>
notation (not to be confused with
<FILEHANDLE>) ran an external program (often
the csh shell) to get the list of filenames.
This led to globbing being tarred with security and performance
concerns. As of v5.6, Perl uses the File::Glob module to glob files,
which solves the security and performance problems of the old
implementation. Globs have C shell semantics on non-Unix systems to
encourage portability. In particular, glob syntax isn't regular
expression syntax—glob uses
? to mean "any single character" and
* to mean "zero or more characters," so
glob("f?o*") matches flo and
flood but not fo.For complex rules about which filenames you want, roll your own
selection mechanism using readdir and regular
expressions.At its simplest, an opendir solution uses
grep to filter the list returned by
readdir:
@files = grep { /\.[ch]$/i } readdir(DH);
As always, the filenames returned don't include the directory. When
you use the filename, prepend the directory name to get the full
pathname:opendir(DH, $dir) or die "Couldn't open $dir for reading: $!";
@files = ( );
while( defined ($file = readdir(DH)) ) {
next unless /\.[ch]$/i;
my $filename = "$dir/$file";
push(@files, $filename) if -T $filename;
}
The following example combines directory reading and filtering with
the efficient sorting technique from Recipe 4.16. It sets @dirs to a sorted
list of the subdirectories in a directory whose names are all
numeric:@dirs = map { $_->[1] } # extract pathnames
sort { $a->[0] <=> $b->[0] } # sort names numeric
grep { -d $_->[1] } # path is a dir
map { [ $_, "$path/$_" ] } # form (name, path)
grep { /^\d+$/ } # just numerics
readdir(DIR); # all files
Recipe 4.16 explains how to read these
strange-looking constructs. As always, formatting and documenting
your code can make it much easier to read and understand.
9.6.4. See Also
The opendir, readdir,
closedir, grep,
map, and sort functions in
perlfunc(1) and in Chapter 29 of
Programming Perl; documentation for the
standard DirHandle module (also in Chapter 32 of
Programming Perl); the "I/O Operators" section
of perlop(1), and the "Filename Globbing
Operator" section of Chapter 2 of
Programming Perl; we talk more about globbing
in Recipe 6.9; Recipe 9.5
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| 9.5. Processing All Files in a Directory |  | 9.7. Processing All Files in a Directory Recursively |
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