Jarkko Hietaniemi > perl-5.8.0 > File::Find

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By perlmonks.org
Module Version: 1.04   Source   Latest Release: perl-5.18.3-RC2

NAME ^

File::Find - Traverse a directory tree.

SYNOPSIS ^

    use File::Find;
    find(\&wanted, @directories_to_seach);
    sub wanted { ... }

    use File::Find;
    finddepth(\&wanted, @directories_to_search);
    sub wanted { ... }

    use File::Find;
    find({ wanted => \&process, follow => 1 }, '.');

DESCRIPTION ^

These are functions for searching through directory trees doing work on each file found similar to the Unix find command. File::Find exports two functions, find and finddepth. They work similarly but have subtle differences.

find
  find(\&wanted,  @directories);
  find(\%options, @directories);

find() does a breadth-first search over the given @directories in the order they are given. In essense, it works from the top down.

For each file or directory found the &wanted subroutine is called (see below for details). Additionally, for each directory found it will go into that directory and continue the search.

finddepth
  finddepth(\&wanted,  @directories);
  finddepth(\%options, @directories);

finddepth() works just like find() except it does a depth-first search. It works from the bottom of the directory tree up.

%options

The first argument to find() is either a hash reference describing the operations to be performed for each file, or a code reference. The code reference is described in "The wanted function" below.

Here are the possible keys for the hash:

wanted

The value should be a code reference. This code reference is described in "The wanted function" below.

bydepth

Reports the name of a directory only AFTER all its entries have been reported. Entry point finddepth() is a shortcut for specifying { bydepth => 1 } in the first argument of find().

preprocess

The value should be a code reference. This code reference is used to preprocess the current directory. The name of currently processed directory is in $File::Find::dir. Your preprocessing function is called after readdir() but before the loop that calls the wanted() function. It is called with a list of strings (actually file/directory names) and is expected to return a list of strings. The code can be used to sort the file/directory names alphabetically, numerically, or to filter out directory entries based on their name alone. When follow or follow_fast are in effect, preprocess is a no-op.

postprocess

The value should be a code reference. It is invoked just before leaving the currently processed directory. It is called in void context with no arguments. The name of the current directory is in $File::Find::dir. This hook is handy for summarizing a directory, such as calculating its disk usage. When follow or follow_fast are in effect, postprocess is a no-op.

follow

Causes symbolic links to be followed. Since directory trees with symbolic links (followed) may contain files more than once and may even have cycles, a hash has to be built up with an entry for each file. This might be expensive both in space and time for a large directory tree. See follow_fast and follow_skip below. If either follow or follow_fast is in effect:

  • It is guaranteed that an lstat has been called before the user's wanted() function is called. This enables fast file checks involving  _.
  • There is a variable $File::Find::fullname which holds the absolute pathname of the file with all symbolic links resolved
follow_fast

This is similar to follow except that it may report some files more than once. It does detect cycles, however. Since only symbolic links have to be hashed, this is much cheaper both in space and time. If processing a file more than once (by the user's wanted() function) is worse than just taking time, the option follow should be used.

follow_skip

follow_skip==1, which is the default, causes all files which are neither directories nor symbolic links to be ignored if they are about to be processed a second time. If a directory or a symbolic link are about to be processed a second time, File::Find dies. follow_skip==0 causes File::Find to die if any file is about to be processed a second time. follow_skip==2 causes File::Find to ignore any duplicate files and directories but to proceed normally otherwise.

dangling_symlinks

If true and a code reference, will be called with the symbolic link name and the directory it lives in as arguments. Otherwise, if true and warnings are on, warning "symbolic_link_name is a dangling symbolic link\n" will be issued. If false, the dangling symbolic link will be silently ignored.

no_chdir

Does not chdir() to each directory as it recurses. The wanted() function will need to be aware of this, of course. In this case, $_ will be the same as $File::Find::name.

untaint

If find is used in taint-mode (-T command line switch or if EUID != UID or if EGID != GID) then internally directory names have to be untainted before they can be chdir'ed to. Therefore they are checked against a regular expression untaint_pattern. Note that all names passed to the user's wanted() function are still tainted. If this option is used while not in taint-mode, untaint is a no-op.

untaint_pattern

See above. This should be set using the qr quoting operator. The default is set to qr|^([-+@\w./]+)$|. Note that the parentheses are vital.

untaint_skip

If set, a directory which fails the untaint_pattern is skipped, including all its sub-directories. The default is to 'die' in such a case.

The wanted function

The wanted() function does whatever verifications you want on each file and directory. It takes no arguments but rather does its work through a collection of variables.

$File::Find::dir is the current directory name,
$_ is the current filename within that directory
$File::Find::name is the complete pathname to the file.

Don't modify these variables.

For example, when examining the file /some/path/foo.ext you will have:

    $File::Find::dir  = /some/path/
    $_                = foo.ext
    $File::Find::name = /some/path/foo.ext

You are chdir()'d to$File::Find::dir when the function is called, unless no_chdir was specified. Note that when changing to directories is in effect the root directory (/) is a somewhat special case inasmuch as the concatenation of $File::Find::dir, '/' and $_ is not literally equal to $File::Find::name. The table below summarizes all variants:

              $File::Find::name  $File::Find::dir  $_
 default      /                  /                 .
 no_chdir=>0  /etc               /                 etc
              /etc/x             /etc              x

 no_chdir=>1  /                  /                 /
              /etc               /                 /etc
              /etc/x             /etc              /etc/x

When <follow> or <follow_fast> are in effect, there is also a $File::Find::fullname. The function may set $File::Find::prune to prune the tree unless bydepth was specified. Unless follow or follow_fast is specified, for compatibility reasons (find.pl, find2perl) there are in addition the following globals available: $File::Find::topdir, $File::Find::topdev, $File::Find::topino, $File::Find::topmode and $File::Find::topnlink.

This library is useful for the find2perl tool, which when fed,

    find2perl / -name .nfs\* -mtime +7 \
        -exec rm -f {} \; -o -fstype nfs -prune

produces something like:

    sub wanted {
        /^\.nfs.*\z/s &&
        (($dev, $ino, $mode, $nlink, $uid, $gid) = lstat($_)) &&
        int(-M _) > 7 &&
        unlink($_)
        ||
        ($nlink || (($dev, $ino, $mode, $nlink, $uid, $gid) = lstat($_))) &&
        $dev < 0 &&
        ($File::Find::prune = 1);
    }

Notice the _ in the above int(-M _): the _ is a magical filehandle that caches the information from the preceding stat(), lstat(), or filetest.

Here's another interesting wanted function. It will find all symbolic links that don't resolve:

    sub wanted {
         -l && !-e && print "bogus link: $File::Find::name\n";
    }

See also the script pfind on CPAN for a nice application of this module.

WARNINGS ^

If you run your program with the -w switch, or if you use the warnings pragma, File::Find will report warnings for several weird situations. You can disable these warnings by putting the statement

    no warnings 'File::Find';

in the appropriate scope. See perllexwarn for more info about lexical warnings.

CAVEAT ^

$dont_use_nlink

You can set the variable $File::Find::dont_use_nlink to 1, if you want to force File::Find to always stat directories. This was used for file systems that do not have an nlink count matching the number of sub-directories. Examples are ISO-9660 (CD-ROM), AFS, HPFS (OS/2 file system), FAT (DOS file system) and a couple of others.

You shouldn't need to set this variable, since File::Find should now detect such file systems on-the-fly and switch itself to using stat. This works even for parts of your file system, like a mounted CD-ROM.

If you do set $File::Find::dont_use_nlink to 1, you will notice slow-downs.

symlinks

Be aware that the option to follow symbolic links can be dangerous. Depending on the structure of the directory tree (including symbolic links to directories) you might traverse a given (physical) directory more than once (only if follow_fast is in effect). Furthermore, deleting or changing files in a symbolically linked directory might cause very unpleasant surprises, since you delete or change files in an unknown directory.

NOTES ^

HISTORY ^

File::Find used to produce incorrect results if called recursively. During the development of perl 5.8 this bug was fixed. The first fixed version of File::Find was 1.01.

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