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()" 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()" works just like "find()" except that is invokes the
&wanted function for a directory 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 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
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
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()"
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:
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:
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,
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:
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 complete
pathname to that directory, and $File::Find::fullname, which holds
the absolute pathname of that directory with all symbolic links resolved,
may or may not end with a ':'.
*
The default "untaint_pattern" (see above) on Mac OS is set to
"qr|^(.+)$|". 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 invisible 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;
Generally, invisible files are system files, unless an odd application
decides to use invisible 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.
