File::Find(3pm) Perl Programmers Reference Guide File::Find(3pm)
NAME
File::Find - Traverse a directory tree.
SYNOPSIS
use File::Find;
find(\&wanted, @directories_to_search);
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 simi-larly similarly
larly but have subtle differences.
find
find(\&wanted, @directories);
find(\%options, @directories);
"find()" does a depth-first search over the given @directories in the order they are given. For
each file or directory found, it calls the &wanted subroutine. (See below for details on how to
use the &wanted function). Additionally, for each directory found, it will "chdir()" into that
directory and continue the search, invoking the &wanted function on each file or subdirectory in
the directory.
finddepth
finddepth(\&wanted, @directories);
finddepth(\%options, @directories);
"finddepth()" works just like "find()" except that is invokes the &wanted function for a direc-tory directory
tory after invoking it for the directory's contents. It does a postorder traversal instead of a
preorder traversal, working from the bottom of the directory tree up where "find()" works from
the top of the tree down.
%options
The first argument to "find()" is either a code reference to your &wanted function, or a hash refer-ence reference
ence describing the operations to be performed for each file. 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 "find-depth()" "finddepth()"
depth()" 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 direc-tory. directory.
tory. The name of the 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 fol-low_fast follow_fast
low_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 _. Note that this guarantee no longer holds
if follow or follow_fast are not set.
* There is a variable $File::Find::fullname which holds the absolute pathname of the file with
all symbolic links resolved. If the link is a dangling symbolic link, then fullname will be
set to "undef".
This is a no-op on Win32.
"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.
This is also a no-op on Win32.
"follow_skip"
"follow_skip==1", which is the default, causes all files which are neither directories nor sym-bolic symbolic
bolic 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. Note that
despite its name, the "wanted()" function is a generic callback function, and does not tell
File::Find if a file is "wanted" or not. In fact, its return value is ignored.
The wanted function 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
Mac OS (Classic) users should note a few differences:
The path separator is ':', not '/', and the current directory is denoted as ':', not '.'. You
should be careful about specifying relative pathnames. While a full path always begins with
a volume name, a relative pathname should always begin with a ':'. If specifying a volume
name only, a trailing ':' is required.
$File::Find::dir is guaranteed to end with a ':'. If $_ contains the name of a directory,
that name may or may not end with a ':'. Likewise, $File::Find::name, which contains the com-plete complete
plete pathname to that directory, and $File::Find::fullname, which holds the absolute path-name pathname
name of that directory with all symbolic links resolved, may or may not end with a ':'.
The default "untaint_pattern" (see above) on Mac OS is set to "qr|^(.+)$|". Note that the
parentheses are vital.
The invisible system file "Icon\015" is ignored. While this file may appear in every direc-tory, directory,
tory, there are some more invisible system files on every volume, which are all located at
the volume root level (i.e. "MacintoshHD:"). These system files are not excluded automati-cally. automatically.
cally. Your filter may use the following code to recognize invisible files or directories
(requires Mac::Files):
use Mac::Files;
# invisible() -- returns 1 if file/directory is invisible,
# 0 if it's visible or undef if an error occurred
sub invisible($) {
my $file = shift;
my ($fileCat, $fileInfo);
my $invisible_flag = 1 << 14;
if ( $fileCat = FSpGetCatInfo($file) ) {
if ($fileInfo = $fileCat->ioFlFndrInfo() ) {
return (($fileInfo->fdFlags & $invisible_flag) && 1);
}
}
return undef;
}
Generally, invisible files are system files, unless an odd application decides to use invisi-ble invisible
ble files for its own purposes. To distinguish such files from system files, you have to look
at the type and creator file attributes. The MacPerl built-in functions "GetFileInfo(FILE)"
and "SetFileInfo(CREATOR, TYPE, FILES)" offer access to these attributes (see MacPerl.pm for
details).
Files that appear on the desktop actually reside in an (hidden) directory named "Desktop
Folder" on the particular disk volume. Note that, although all desktop files appear to be on
the same "virtual" desktop, each disk volume actually maintains its own "Desktop Folder"
directory.
BUGS AND CAVEATS
Despite the name of the "finddepth()" function, both "find()" and "finddepth()" perform a depth-first
search of the directory hierarchy.
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.
perl v5.8.8 2001-09-21 File::Find(3pm)
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