File::Find
File::Find(3) Perl Programmers Reference Guide File::Find(3)
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 similarly
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 directory after invoking it for the direc-
tory’s contents. It does a postorder traversal instead of a pre-
order 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 reference 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 "finddepth()" is a shortcut for speci-
fying "<{ 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 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 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 _. 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 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. Note that despite its name, the "wanted()" func-
tion 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 directo-
ries 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 filehan-
dle 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 "warn-
ings" pragma, File::Find will report warnings for several weird situa-
tions. 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 num-
ber 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) direc-
tory more than once (only if "follow_fast" is in effect). Further-
more, 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 trail-
ing ’:’ is required.
· $File::Find::dir is guaranteed to end with a ’:’. If $_ con-
tains the name of a directory, that name may or may not end
with a ’:’. Likewise, $File::Find::name, which contains the
complete pathname to that directory, and $File::Find::full-
name, which holds the absolute pathname of that directory with
all symbolic links resolved, may or may not end with a ’:’.
· The default "untaint_pattern" (see above) on Mac OS is set to
"qr│^(.+)$│". Note that the parentheses are vital.
· The invisible system file "Icon\015" is ignored. While this
file may appear in every directory, there are some more invis-
ible system files on every volume, which are all located at
the volume root level (i.e. "MacintoshHD:"). These system
files are not excluded automatically. 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 invisible files for its own pur-
poses. 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(CRE-
ATOR, TYPE, FILES)" offer access to these attributes (see
MacPerl.pm for details).
Files that appear on the desktop actually reside in an (hid-
den) 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 main-
tains 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(3)
