File::Find(3p) Perl Programmers Reference Guide File::Find(3p) #
File::Find(3p) Perl Programmers Reference Guide File::Find(3p)
NNAAMMEE #
File::Find - Traverse a directory tree.
SSYYNNOOPPSSIISS #
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 }, '.');
DDEESSCCRRIIPPTTIIOONN #
These are functions for searching through directory trees doing work on
each file found similar to the Unix _f_i_n_d command. File::Find exports two
functions, "find" and "finddepth". They work similarly but have subtle
differences.
ffiinndd
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.
ffiinnddddeepptthh
finddepth(\&wanted, @directories);
finddepth(\%options, @directories);
"finddepth()" works just like "find()" except that it invokes the
&wanted function for a directory _a_f_t_e_r 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.
Despite the name of the "finddepth()" function, both "find()" and
"finddepth()" perform a depth-first search of the directory hierarchy.
%%ooppttiioonnss 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. The &wanted subroutine is
mandatory.
"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 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 _f_o_l_l_o_w or _f_o_l_l_o_w___f_a_s_t 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 _f_o_l_l_o_w or _f_o_l_l_o_w___f_a_s_t 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
_f_o_l_l_o_w or _f_o_l_l_o_w___f_a_s_t is in effect:
• It is guaranteed that an _l_s_t_a_t 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
_f_o_l_l_o_w or _f_o_l_l_o_w___f_a_s_t 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 _f_o_l_l_o_w 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 _f_o_l_l_o_w 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"
Specifies what to do with symbolic links whose target doesn't exist.
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, a warning of the form "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 $File::Find::name.
"untaint"
If find is used in taint-mode (-T command line switch or if EUID !=
UID or if EGID != GID), then internally directory names have to be
untainted before they can be "chdir"'d to. Therefore they are checked
against a regular expression _u_n_t_a_i_n_t___p_a_t_t_e_r_n. Note that all names
passed to the user's "wanted()" function are still tainted. If this
option is used while not in taint-mode, "untaint" is a no-op.
"untaint_pattern"
See above. This should be set using the "qr" quoting operator. The
default is set to "qr|^([-+@\w./]+)$|". Note that the parentheses
are vital.
"untaint_skip"
If set, a directory which fails the _u_n_t_a_i_n_t___p_a_t_t_e_r_n is skipped,
including all its sub-directories. The default is to "die" in such a
case.
TThhee wwaanntteedd ffuunnccttiioonn 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 nnoott 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.
The above variables have all been localized and may be changed without
affecting data outside of the wanted function.
For example, when examining the file _/_s_o_m_e_/_p_a_t_h_/_f_o_o_._e_x_t you will have:
$File::Find::dir = /some/path/
$_ = foo.ext
$File::Find::name = /some/path/foo.ext
You are cchhddiirr(())'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 $File::Find::topnlink.
This library is useful for the "find2perl" tool (distributed as part of
the App-find2perl CPAN distribution), which when fed,
find2perl / -name .nfs\* -mtime +7 \
-exec rm -f {} \; -o -fstype nfs -prune
produces something like:
sub wanted {
/^\.nfs.*\z/s &&
(($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";
}
Note that you may mix directories and (non-directory) files in the list
of directories to be searched by the "wanted()" function.
find(\&wanted, "./foo", "./bar", "./baz/epsilon");
In the example above, no file in _._/_b_a_z_/ other than _._/_b_a_z_/_e_p_s_i_l_o_n will be
evaluated by "wanted()".
See also the script "pfind" on CPAN for a nice application of this
module.
WWAARRNNIINNGGSS #
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 warnings for more info about lexical
warnings.
BBUUGGSS AANNDD CCAAVVEEAATTSS #
$dont_use_nlink
You can set the variable $File::Find::dont_use_nlink to 0 if you are
sure the filesystem you are scanning reflects the number of
subdirectories in the parent directory's "nlink" count.
If you do set $File::Find::dont_use_nlink to 0, you may notice an
improvement in speed at the risk of not recursing into subdirectories
if a filesystem doesn't populate "nlink" as expected.
$File::Find::dont_use_nlink now defaults to 1 on all platforms.
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.
HHIISSTTOORRYY #
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.
SSEEEE AALLSSOO #
ffiinndd(1), find2perl.
perl v5.36.3 2023-02-15 File::Find(3p)