1PERLFAQ5(1) Perl Programmers Reference Guide PERLFAQ5(1)
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6 perlfaq5 - Files and Formats
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9 This section deals with I/O and the "f" issues: filehandles, flushing,
10 formats, and footers.
11 How do I flush/unbuffer an output filehandle? Why must I do this?
13 (contributed by brian d foy)
14 You might like to read Mark Jason Dominus's "Suffering From Buffering"
16 at http://perl.plover.com/FAQs/Buffering.html .
17 Perl normally buffers output so it doesn't make a system call for every
19 bit of output. By saving up output, it makes fewer expensive system
20 calls. For instance, in this little bit of code, you want to print a
21 dot to the screen for every line you process to watch the progress of
22 your program. Instead of seeing a dot for every line, Perl buffers the
23 output and you have a long wait before you see a row of 50 dots all at
24 once:
25 # long wait, then row of dots all at once
27 while( <> ) {
28 print ".";
29 print "\n" unless ++$count % 50;
30 #... expensive line processing operations
32 }
33 To get around this, you have to unbuffer the output filehandle, in this
35 case, "STDOUT". You can set the special variable $| to a true value
36 (mnemonic: making your filehandles "piping hot"):
37 $|++;
39 # dot shown immediately
41 while( <> ) {
42 print ".";
43 print "\n" unless ++$count % 50;
44 #... expensive line processing operations
46 }
47 The $| is one of the per-filehandle special variables, so each
49 filehandle has its own copy of its value. If you want to merge standard
50 output and standard error for instance, you have to unbuffer each
51 (although STDERR might be unbuffered by default):
52 {
54 my $previous_default = select(STDOUT); # save previous default
55 $|++; # autoflush STDOUT
56 select(STDERR);
57 $|++; # autoflush STDERR, to be sure
58 select($previous_default); # restore previous default
59 }
60 # now should alternate . and +
62 while( 1 )
63 {
64 sleep 1;
65 print STDOUT ".";
66 print STDERR "+";
67 print STDOUT "\n" unless ++$count % 25;
68 }
69 Besides the $| special variable, you can use "binmode" to give your
71 filehandle a ":unix" layer, which is unbuffered:
72 binmode( STDOUT, ":unix" );
74 while( 1 ) {
76 sleep 1;
77 print ".";
78 print "\n" unless ++$count % 50;
79 }
80 For more information on output layers, see the entries for "binmode"
82 and "open" in perlfunc, and the "PerlIO" module documentation.
83 If you are using "IO::Handle" or one of its subclasses, you can call
85 the "autoflush" method to change the settings of the filehandle:
86 use IO::Handle;
88 open my( $io_fh ), ">", "output.txt";
89 $io_fh->autoflush(1);
90 The "IO::Handle" objects also have a "flush" method. You can flush the
92 buffer any time you want without auto-buffering
93 $io_fh->flush;
95 How do I change, delete, or insert a line in a file, or append to the
97 beginning of a file?
98 (contributed by brian d foy)
99 The basic idea of inserting, changing, or deleting a line from a text
101 file involves reading and printing the file to the point you want to
102 make the change, making the change, then reading and printing the rest
103 of the file. Perl doesn't provide random access to lines (especially
104 since the record input separator, $/, is mutable), although modules
105 such as "Tie::File" can fake it.
106 A Perl program to do these tasks takes the basic form of opening a
108 file, printing its lines, then closing the file:
109 open my $in, '<', $file or die "Can't read old file: $!";
111 open my $out, '>', "$file.new" or die "Can't write new file: $!";
112 while( <$in> )
114 {
115 print $out $_;
116 }
117 close $out;
119 Within that basic form, add the parts that you need to insert, change,
121 or delete lines.
122 To prepend lines to the beginning, print those lines before you enter
124 the loop that prints the existing lines.
125 open my $in, '<', $file or die "Can't read old file: $!";
127 open my $out, '>', "$file.new" or die "Can't write new file: $!";
128 print $out "# Add this line to the top\n"; # <--- HERE'S THE MAGIC
130 while( <$in> )
132 {
133 print $out $_;
134 }
135 close $out;
137 To change existing lines, insert the code to modify the lines inside
139 the "while" loop. In this case, the code finds all lowercased versions
140 of "perl" and uppercases them. The happens for every line, so be sure
141 that you're supposed to do that on every line!
142 open my $in, '<', $file or die "Can't read old file: $!";
144 open my $out, '>', "$file.new" or die "Can't write new file: $!";
145 print $out "# Add this line to the top\n";
147 while( <$in> )
149 {
150 s/\b(perl)\b/Perl/g;
151 print $out $_;
152 }
153 close $out;
155 To change only a particular line, the input line number, $., is useful.
157 First read and print the lines up to the one you want to change. Next,
158 read the single line you want to change, change it, and print it. After
159 that, read the rest of the lines and print those:
160 while( <$in> ) # print the lines before the change
162 {
163 print $out $_;
164 last if $. == 4; # line number before change
165 }
166 my $line = <$in>;
168 $line =~ s/\b(perl)\b/Perl/g;
169 print $out $line;
170 while( <$in> ) # print the rest of the lines
172 {
173 print $out $_;
174 }
175 To skip lines, use the looping controls. The "next" in this example
177 skips comment lines, and the "last" stops all processing once it
178 encounters either "__END__" or "__DATA__".
179 while( <$in> )
181 {
182 next if /^\s+#/; # skip comment lines
183 last if /^__(END|DATA)__$/; # stop at end of code marker
184 print $out $_;
185 }
186 Do the same sort of thing to delete a particular line by using "next"
188 to skip the lines you don't want to show up in the output. This example
189 skips every fifth line:
190 while( <$in> )
192 {
193 next unless $. % 5;
194 print $out $_;
195 }
196 If, for some odd reason, you really want to see the whole file at once
198 rather than processing line-by-line, you can slurp it in (as long as
199 you can fit the whole thing in memory!):
200 open my $in, '<', $file or die "Can't read old file: $!"
202 open my $out, '>', "$file.new" or die "Can't write new file: $!";
203 my @lines = do { local $/; <$in> }; # slurp!
205 # do your magic here
207 print $out @lines;
209 Modules such as "File::Slurp" and "Tie::File" can help with that too.
211 If you can, however, avoid reading the entire file at once. Perl won't
212 give that memory back to the operating system until the process
213 finishes.
214 You can also use Perl one-liners to modify a file in-place. The
216 following changes all 'Fred' to 'Barney' in inFile.txt, overwriting the
217 file with the new contents. With the "-p" switch, Perl wraps a "while"
218 loop around the code you specify with "-e", and "-i" turns on in-place
219 editing. The current line is in $_. With "-p", Perl automatically
220 prints the value of $_ at the end of the loop. See perlrun for more
221 details.
222 perl -pi -e 's/Fred/Barney/' inFile.txt
224 To make a backup of "inFile.txt", give "-i" a file extension to add:
226 perl -pi.bak -e 's/Fred/Barney/' inFile.txt
228 To change only the fifth line, you can add a test checking $., the
230 input line number, then only perform the operation when the test
231 passes:
232 perl -pi -e 's/Fred/Barney/ if $. == 5' inFile.txt
234 To add lines before a certain line, you can add a line (or lines!)
236 before Perl prints $_:
237 perl -pi -e 'print "Put before third line\n" if $. == 3' inFile.txt
239 You can even add a line to the beginning of a file, since the current
241 line prints at the end of the loop:
242 perl -pi -e 'print "Put before first line\n" if $. == 1' inFile.txt
244 To insert a line after one already in the file, use the "-n" switch.
246 It's just like "-p" except that it doesn't print $_ at the end of the
247 loop, so you have to do that yourself. In this case, print $_ first,
248 then print the line that you want to add.
249 perl -ni -e 'print; print "Put after fifth line\n" if $. == 5' inFile.txt
251 To delete lines, only print the ones that you want.
253 perl -ni -e 'print unless /d/' inFile.txt
255 ... or ...
257 perl -pi -e 'next unless /d/' inFile.txt
259 How do I count the number of lines in a file?
261 (contributed by brian d foy)
262 Conceptually, the easiest way to count the lines in a file is to simply
264 read them and count them:
265 my $count = 0;
267 while( <$fh> ) { $count++; }
268 You don't really have to count them yourself, though, since Perl
270 already does that with the $. variable, which is the current line
271 number from the last filehandle read:
272 1 while( <$fh> );
274 my $count = $.;
275 If you want to use $., you can reduce it to a simple one-liner, like
277 one of these:
278 % perl -lne '} print $.; {' file
280 % perl -lne 'END { print $. }' file
282 Those can be rather inefficient though. If they aren't fast enough for
284 you, you might just read chunks of data and count the number of
285 newlines:
286 my $lines = 0;
288 open my($fh), '<:raw', $filename or die "Can't open $filename: $!";
289 while( sysread $fh, $buffer, 4096 ) {
290 $lines += ( $buffer =~ tr/\n// );
291 }
292 close FILE;
293 However, that doesn't work if the line ending isn't a newline. You
295 might change that "tr///" to a "s///" so you can count the number of
296 times the input record separator, $/, shows up:
297 my $lines = 0;
299 open my($fh), '<:raw', $filename or die "Can't open $filename: $!";
300 while( sysread $fh, $buffer, 4096 ) {
301 $lines += ( $buffer =~ s|$/||g; );
302 }
303 close FILE;
304 If you don't mind shelling out, the "wc" command is usually the
306 fastest, even with the extra interprocess overhead. Ensure that you
307 have an untainted filename though:
308 #!perl -T
310 $ENV{PATH} = undef;
312 my $lines;
314 if( $filename =~ /^([0-9a-z_.]+)\z/ ) {
315 $lines = `/usr/bin/wc -l $1`
316 chomp $lines;
317 }
318 How do I delete the last N lines from a file?
320 (contributed by brian d foy)
321 The easiest conceptual solution is to count the lines in the file then
323 start at the beginning and print the number of lines (minus the last N)
324 to a new file.
325 Most often, the real question is how you can delete the last N lines
327 without making more than one pass over the file, or how to do it
328 without a lot of copying. The easy concept is the hard reality when you
329 might have millions of lines in your file.
330 One trick is to use "File::ReadBackwards", which starts at the end of
332 the file. That module provides an object that wraps the real filehandle
333 to make it easy for you to move around the file. Once you get to the
334 spot you need, you can get the actual filehandle and work with it as
335 normal. In this case, you get the file position at the end of the last
336 line you want to keep and truncate the file to that point:
337 use File::ReadBackwards;
339 my $filename = 'test.txt';
341 my $Lines_to_truncate = 2;
342 my $bw = File::ReadBackwards->new( $filename )
344 or die "Could not read backwards in [$filename]: $!";
345 my $lines_from_end = 0;
347 until( $bw->eof or $lines_from_end == $Lines_to_truncate )
348 {
349 print "Got: ", $bw->readline;
350 $lines_from_end++;
351 }
352 truncate( $filename, $bw->tell );
354 The "File::ReadBackwards" module also has the advantage of setting the
356 input record separator to a regular expression.
357 You can also use the "Tie::File" module which lets you access the lines
359 through a tied array. You can use normal array operations to modify
360 your file, including setting the last index and using "splice".
361 How can I use Perl's "-i" option from within a program?
363 "-i" sets the value of Perl's $^I variable, which in turn affects the
364 behavior of "<>"; see perlrun for more details. By modifying the
365 appropriate variables directly, you can get the same behavior within a
366 larger program. For example:
367 # ...
369 {
370 local($^I, @ARGV) = ('.orig', glob("*.c"));
371 while (<>) {
372 if ($. == 1) {
373 print "This line should appear at the top of each file\n";
374 }
375 s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case
376 print;
377 close ARGV if eof; # Reset $.
378 }
379 }
380 # $^I and @ARGV return to their old values here
381 This block modifies all the ".c" files in the current directory,
383 leaving a backup of the original data from each file in a new ".c.orig"
384 file.
385 How can I copy a file?
387 (contributed by brian d foy)
388 Use the "File::Copy" module. It comes with Perl and can do a true copy
390 across file systems, and it does its magic in a portable fashion.
391 use File::Copy;
393 copy( $original, $new_copy ) or die "Copy failed: $!";
395 If you can't use "File::Copy", you'll have to do the work yourself:
397 open the original file, open the destination file, then print to the
398 destination file as you read the original. You also have to remember to
399 copy the permissions, owner, and group to the new file.
400 How do I make a temporary file name?
402 If you don't need to know the name of the file, you can use "open()"
403 with "undef" in place of the file name. In Perl 5.8 or later, the
404 "open()" function creates an anonymous temporary file:
405 open my $tmp, '+>', undef or die $!;
407 Otherwise, you can use the File::Temp module.
409 use File::Temp qw/ tempfile tempdir /;
411 my $dir = tempdir( CLEANUP => 1 );
413 ($fh, $filename) = tempfile( DIR => $dir );
414 # or if you don't need to know the filename
416 my $fh = tempfile( DIR => $dir );
418 The File::Temp has been a standard module since Perl 5.6.1. If you
420 don't have a modern enough Perl installed, use the "new_tmpfile" class
421 method from the IO::File module to get a filehandle opened for reading
422 and writing. Use it if you don't need to know the file's name:
423 use IO::File;
425 my $fh = IO::File->new_tmpfile()
426 or die "Unable to make new temporary file: $!";
427 If you're committed to creating a temporary file by hand, use the
429 process ID and/or the current time-value. If you need to have many
430 temporary files in one process, use a counter:
431 BEGIN {
433 use Fcntl;
434 my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMPDIR} || $ENV{TEMP};
435 my $base_name = sprintf "%s/%d-%d-0000", $temp_dir, $$, time;
436 sub temp_file {
438 local *FH;
439 my $count = 0;
440 until( defined(fileno(FH)) || $count++ > 100 ) {
441 $base_name =~ s/-(\d+)$/"-" . (1 + $1)/e;
442 # O_EXCL is required for security reasons.
443 sysopen my($fh), $base_name, O_WRONLY|O_EXCL|O_CREAT;
444 }
445 if( defined fileno($fh) ) {
447 return ($fh, $base_name);
448 }
449 else {
450 return ();
451 }
452 }
453 }
455 How can I manipulate fixed-record-length files?
457 The most efficient way is using pack() and unpack(). This is faster
458 than using substr() when taking many, many strings. It is slower for
459 just a few.
460 Here is a sample chunk of code to break up and put back together again
462 some fixed-format input lines, in this case from the output of a
463 normal, Berkeley-style ps:
464 # sample input line:
466 # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what
467 my $PS_T = 'A6 A4 A7 A5 A*';
468 open my $ps, '-|', 'ps';
469 print scalar <$ps>;
470 my @fields = qw( pid tt stat time command );
471 while (<$ps>) {
472 my %process;
473 @process{@fields} = unpack($PS_T, $_);
474 for my $field ( @fields ) {
475 print "$field: <$process{$field}>\n";
476 }
477 print 'line=', pack($PS_T, @process{@fields} ), "\n";
478 }
479 We've used a hash slice in order to easily handle the fields of each
481 row. Storing the keys in an array means it's easy to operate on them
482 as a group or loop over them with for. It also avoids polluting the
483 program with global variables and using symbolic references.
484 How can I make a filehandle local to a subroutine? How do I pass
486 filehandles between subroutines? How do I make an array of
487 filehandles?
488 As of perl5.6, open() autovivifies file and directory handles as
489 references if you pass it an uninitialized scalar variable. You can
490 then pass these references just like any other scalar, and use them in
491 the place of named handles.
492 open my $fh, $file_name;
494 open local $fh, $file_name;
496 print $fh "Hello World!\n";
498 process_file( $fh );
500 If you like, you can store these filehandles in an array or a hash. If
502 you access them directly, they aren't simple scalars and you need to
503 give "print" a little help by placing the filehandle reference in
504 braces. Perl can only figure it out on its own when the filehandle
505 reference is a simple scalar.
506 my @fhs = ( $fh1, $fh2, $fh3 );
508 for( $i = 0; $i <= $#fhs; $i++ ) {
510 print {$fhs[$i]} "just another Perl answer, \n";
511 }
512 Before perl5.6, you had to deal with various typeglob idioms which you
514 may see in older code.
515 open FILE, "> $filename";
517 process_typeglob( *FILE );
518 process_reference( \*FILE );
519 sub process_typeglob { local *FH = shift; print FH "Typeglob!" }
521 sub process_reference { local $fh = shift; print $fh "Reference!" }
522 If you want to create many anonymous handles, you should check out the
524 Symbol or IO::Handle modules.
525 How can I use a filehandle indirectly?
527 An indirect filehandle is using something other than a symbol in a
528 place that a filehandle is expected. Here are ways to get indirect
529 filehandles:
530 $fh = SOME_FH; # bareword is strict-subs hostile
532 $fh = "SOME_FH"; # strict-refs hostile; same package only
533 $fh = *SOME_FH; # typeglob
534 $fh = \*SOME_FH; # ref to typeglob (bless-able)
535 $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob
536 Or, you can use the "new" method from one of the IO::* modules to
538 create an anonymous filehandle, store that in a scalar variable, and
539 use it as though it were a normal filehandle.
540 use IO::Handle; # 5.004 or higher
542 my $fh = IO::Handle->new();
543 Then use any of those as you would a normal filehandle. Anywhere that
545 Perl is expecting a filehandle, an indirect filehandle may be used
546 instead. An indirect filehandle is just a scalar variable that contains
547 a filehandle. Functions like "print", "open", "seek", or the "<FH>"
548 diamond operator will accept either a named filehandle or a scalar
549 variable containing one:
550 ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR);
552 print $ofh "Type it: ";
553 my $got = <$ifh>
554 print $efh "What was that: $got";
555 If you're passing a filehandle to a function, you can write the
557 function in two ways:
558 sub accept_fh {
560 my $fh = shift;
561 print $fh "Sending to indirect filehandle\n";
562 }
563 Or it can localize a typeglob and use the filehandle directly:
565 sub accept_fh {
567 local *FH = shift;
568 print FH "Sending to localized filehandle\n";
569 }
570 Both styles work with either objects or typeglobs of real filehandles.
572 (They might also work with strings under some circumstances, but this
573 is risky.)
574 accept_fh(*STDOUT);
576 accept_fh($handle);
577 In the examples above, we assigned the filehandle to a scalar variable
579 before using it. That is because only simple scalar variables, not
580 expressions or subscripts of hashes or arrays, can be used with built-
581 ins like "print", "printf", or the diamond operator. Using something
582 other than a simple scalar variable as a filehandle is illegal and
583 won't even compile:
584 my @fd = (*STDIN, *STDOUT, *STDERR);
586 print $fd[1] "Type it: "; # WRONG
587 my $got = <$fd[0]> # WRONG
588 print $fd[2] "What was that: $got"; # WRONG
589 With "print" and "printf", you get around this by using a block and an
591 expression where you would place the filehandle:
592 print { $fd[1] } "funny stuff\n";
594 printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559;
595 # Pity the poor deadbeef.
596 That block is a proper block like any other, so you can put more
598 complicated code there. This sends the message out to one of two
599 places:
600 my $ok = -x "/bin/cat";
602 print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n";
603 print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n";
604 This approach of treating "print" and "printf" like object methods
606 calls doesn't work for the diamond operator. That's because it's a real
607 operator, not just a function with a comma-less argument. Assuming
608 you've been storing typeglobs in your structure as we did above, you
609 can use the built-in function named "readline" to read a record just as
610 "<>" does. Given the initialization shown above for @fd, this would
611 work, but only because readline() requires a typeglob. It doesn't work
612 with objects or strings, which might be a bug we haven't fixed yet.
613 $got = readline($fd[0]);
615 Let it be noted that the flakiness of indirect filehandles is not
617 related to whether they're strings, typeglobs, objects, or anything
618 else. It's the syntax of the fundamental operators. Playing the object
619 game doesn't help you at all here.
620 How can I set up a footer format to be used with write()?
622 There's no builtin way to do this, but perlform has a couple of
623 techniques to make it possible for the intrepid hacker.
624 How can I write() into a string?
626 See "Accessing Formatting Internals" in perlform for an "swrite()"
627 function.
628 How can I open a filehandle to a string?
630 (contributed by Peter J. Holzer, hjp-usenet2@hjp.at)
631 Since Perl 5.8.0 a file handle referring to a string can be created by
633 calling open with a reference to that string instead of the filename.
634 This file handle can then be used to read from or write to the string:
635 open(my $fh, '>', \$string) or die "Could not open string for writing";
637 print $fh "foo\n";
638 print $fh "bar\n"; # $string now contains "foo\nbar\n"
639 open(my $fh, '<', \$string) or die "Could not open string for reading";
641 my $x = <$fh>; # $x now contains "foo\n"
642 With older versions of Perl, the "IO::String" module provides similar
644 functionality.
645 How can I output my numbers with commas added?
647 (contributed by brian d foy and Benjamin Goldberg)
648 You can use Number::Format to separate places in a number. It handles
650 locale information for those of you who want to insert full stops
651 instead (or anything else that they want to use, really).
652 This subroutine will add commas to your number:
654 sub commify {
656 local $_ = shift;
657 1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
658 return $_;
659 }
660 This regex from Benjamin Goldberg will add commas to numbers:
662 s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g;
664 It is easier to see with comments:
666 s/(
668 ^[-+]? # beginning of number.
669 \d+? # first digits before first comma
670 (?= # followed by, (but not included in the match) :
671 (?>(?:\d{3})+) # some positive multiple of three digits.
672 (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever.
673 )
674 | # or:
675 \G\d{3} # after the last group, get three digits
676 (?=\d) # but they have to have more digits after them.
677 )/$1,/xg;
678 How can I translate tildes (~) in a filename?
680 Use the <> ("glob()") operator, documented in perlfunc. Versions of
681 Perl older than 5.6 require that you have a shell installed that groks
682 tildes. Later versions of Perl have this feature built in. The
683 "File::KGlob" module (available from CPAN) gives more portable glob
684 functionality.
685 Within Perl, you may use this directly:
687 $filename =~ s{
689 ^ ~ # find a leading tilde
690 ( # save this in $1
691 [^/] # a non-slash character
692 * # repeated 0 or more times (0 means me)
693 )
694 }{
695 $1
696 ? (getpwnam($1))[7]
697 : ( $ENV{HOME} || $ENV{LOGDIR} )
698 }ex;
699 How come when I open a file read-write it wipes it out?
701 Because you're using something like this, which truncates the file and
702 then gives you read-write access:
703 open my $fh, '+>', '/path/name'; # WRONG (almost always)
705 Whoops. You should instead use this, which will fail if the file
707 doesn't exist.
708 open my $fh, '+<', '/path/name'; # open for update
710 Using ">" always clobbers or creates. Using "<" never does either. The
712 "+" doesn't change this.
713 Here are examples of many kinds of file opens. Those using sysopen()
715 all assume
716 use Fcntl;
718 To open file for reading:
720 open my $fh, '<', $path or die $!;
722 sysopen my $fh, $path, O_RDONLY or die $!;
723 To open file for writing, create new file if needed or else truncate
725 old file:
726 open my $fh, '>', $path or die $!;
728 sysopen my $fh, $path, O_WRONLY|O_TRUNC|O_CREAT or die $!;
729 sysopen my $fh, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666 or die $!;
730 To open file for writing, create new file, file must not exist:
732 sysopen my $fh, $path, O_WRONLY|O_EXCL|O_CREAT or die $!;
734 sysopen my $fh, $path, O_WRONLY|O_EXCL|O_CREAT, 0666 or die $!;
735 To open file for appending, create if necessary:
737 open my $fh, '>>' $path or die $!;
739 sysopen my $fh, $path, O_WRONLY|O_APPEND|O_CREAT or die $!;
740 sysopen my $fh, $path, O_WRONLY|O_APPEND|O_CREAT, 0666 or die $!;
741 To open file for appending, file must exist:
743 sysopen my $fh, $path, O_WRONLY|O_APPEND or die $!;
745 To open file for update, file must exist:
747 open my $fh, '+<', $path or die $!;
749 sysopen my $fh, $path, O_RDWR or die $!;
750 To open file for update, create file if necessary:
752 sysopen my $fh, $path, O_RDWR|O_CREAT or die $!;
754 sysopen my $fh, $path, O_RDWR|O_CREAT, 0666 or die $!;
755 To open file for update, file must not exist:
757 sysopen my $fh, $path, O_RDWR|O_EXCL|O_CREAT or die $!;
759 sysopen my $fh, $path, O_RDWR|O_EXCL|O_CREAT, 0666 or die $!;
760 To open a file without blocking, creating if necessary:
762 sysopen my $fh, '/foo/somefile', O_WRONLY|O_NDELAY|O_CREAT
764 or die "can't open /foo/somefile: $!":
765 Be warned that neither creation nor deletion of files is guaranteed to
767 be an atomic operation over NFS. That is, two processes might both
768 successfully create or unlink the same file! Therefore O_EXCL isn't as
769 exclusive as you might wish.
770 See also the new perlopentut.
772 Why do I sometimes get an "Argument list too long" when I use <*>?
774 The "<>" operator performs a globbing operation (see above). In Perl
775 versions earlier than v5.6.0, the internal glob() operator forks csh(1)
776 to do the actual glob expansion, but csh can't handle more than 127
777 items and so gives the error message "Argument list too long". People
778 who installed tcsh as csh won't have this problem, but their users may
779 be surprised by it.
780 To get around this, either upgrade to Perl v5.6.0 or later, do the glob
782 yourself with readdir() and patterns, or use a module like File::KGlob,
783 one that doesn't use the shell to do globbing.
784 Is there a leak/bug in glob()?
786 (contributed by brian d foy)
787 Starting with Perl 5.6.0, "glob" is implemented internally rather than
789 relying on an external resource. As such, memory issues with "glob"
790 aren't a problem in modern perls.
791 How can I open a file with a leading ">" or trailing blanks?
793 (contributed by Brian McCauley)
794 The special two argument form of Perl's open() function ignores
796 trailing blanks in filenames and infers the mode from certain leading
797 characters (or a trailing "|"). In older versions of Perl this was the
798 only version of open() and so it is prevalent in old code and books.
799 Unless you have a particular reason to use the two argument form you
801 should use the three argument form of open() which does not treat any
802 characters in the filename as special.
803 open my $fh, "<", " file "; # filename is " file "
805 open my $fh, ">", ">file"; # filename is ">file"
806 How can I reliably rename a file?
808 If your operating system supports a proper mv(1) utility or its
809 functional equivalent, this works:
810 rename($old, $new) or system("mv", $old, $new);
812 It may be more portable to use the "File::Copy" module instead. You
814 just copy to the new file to the new name (checking return values),
815 then delete the old one. This isn't really the same semantically as a
816 "rename()", which preserves meta-information like permissions,
817 timestamps, inode info, etc.
818 How can I lock a file?
820 Perl's builtin flock() function (see perlfunc for details) will call
821 flock(2) if that exists, fcntl(2) if it doesn't (on perl version 5.004
822 and later), and lockf(3) if neither of the two previous system calls
823 exists. On some systems, it may even use a different form of native
824 locking. Here are some gotchas with Perl's flock():
825 1. Produces a fatal error if none of the three system calls (or their
827 close equivalent) exists.
828 2. lockf(3) does not provide shared locking, and requires that the
830 filehandle be open for writing (or appending, or read/writing).
831 3. Some versions of flock() can't lock files over a network (e.g. on
833 NFS file systems), so you'd need to force the use of fcntl(2) when
834 you build Perl. But even this is dubious at best. See the flock
835 entry of perlfunc and the INSTALL file in the source distribution
836 for information on building Perl to do this.
837 Two potentially non-obvious but traditional flock semantics are
839 that it waits indefinitely until the lock is granted, and that its
840 locks are merely advisory. Such discretionary locks are more
841 flexible, but offer fewer guarantees. This means that files locked
842 with flock() may be modified by programs that do not also use
843 flock(). Cars that stop for red lights get on well with each other,
844 but not with cars that don't stop for red lights. See the perlport
845 manpage, your port's specific documentation, or your system-
846 specific local manpages for details. It's best to assume
847 traditional behavior if you're writing portable programs. (If
848 you're not, you should as always feel perfectly free to write for
849 your own system's idiosyncrasies (sometimes called "features").
850 Slavish adherence to portability concerns shouldn't get in the way
851 of your getting your job done.)
852 For more information on file locking, see also "File Locking" in
854 perlopentut if you have it (new for 5.6).
855 Why can't I just open(FH, ">file.lock")?
857 A common bit of code NOT TO USE is this:
858 sleep(3) while -e 'file.lock'; # PLEASE DO NOT USE
860 open my $lock, '>', 'file.lock'; # THIS BROKEN CODE
861 This is a classic race condition: you take two steps to do something
863 which must be done in one. That's why computer hardware provides an
864 atomic test-and-set instruction. In theory, this "ought" to work:
865 sysopen my $fh, "file.lock", O_WRONLY|O_EXCL|O_CREAT
867 or die "can't open file.lock: $!";
868 except that lamentably, file creation (and deletion) is not atomic over
870 NFS, so this won't work (at least, not every time) over the net.
871 Various schemes involving link() have been suggested, but these tend to
872 involve busy-wait, which is also less than desirable.
873 I still don't get locking. I just want to increment the number in the file.
875 How can I do this?
876 Didn't anyone ever tell you web-page hit counters were useless? They
877 don't count number of hits, they're a waste of time, and they serve
878 only to stroke the writer's vanity. It's better to pick a random
879 number; they're more realistic.
880 Anyway, this is what you can do if you can't help yourself.
882 use Fcntl qw(:DEFAULT :flock);
884 sysopen my $fh, "numfile", O_RDWR|O_CREAT or die "can't open numfile: $!";
885 flock $fh, LOCK_EX or die "can't flock numfile: $!";
886 my $num = <$fh> || 0;
887 seek $fh, 0, 0 or die "can't rewind numfile: $!";
888 truncate $fh, 0 or die "can't truncate numfile: $!";
889 (print $fh $num+1, "\n") or die "can't write numfile: $!";
890 close $fh or die "can't close numfile: $!";
891 Here's a much better web-page hit counter:
893 $hits = int( (time() - 850_000_000) / rand(1_000) );
895 If the count doesn't impress your friends, then the code might. :-)
897 All I want to do is append a small amount of text to the end of a file. Do
899 I still have to use locking?
900 If you are on a system that correctly implements "flock" and you use
901 the example appending code from "perldoc -f flock" everything will be
902 OK even if the OS you are on doesn't implement append mode correctly
903 (if such a system exists.) So if you are happy to restrict yourself to
904 OSs that implement "flock" (and that's not really much of a
905 restriction) then that is what you should do.
906 If you know you are only going to use a system that does correctly
908 implement appending (i.e. not Win32) then you can omit the "seek" from
909 the code in the previous answer.
910 If you know you are only writing code to run on an OS and filesystem
912 that does implement append mode correctly (a local filesystem on a
913 modern Unix for example), and you keep the file in block-buffered mode
914 and you write less than one buffer-full of output between each manual
915 flushing of the buffer then each bufferload is almost guaranteed to be
916 written to the end of the file in one chunk without getting
917 intermingled with anyone else's output. You can also use the "syswrite"
918 function which is simply a wrapper around your system's write(2) system
919 call.
920 There is still a small theoretical chance that a signal will interrupt
922 the system level "write()" operation before completion. There is also a
923 possibility that some STDIO implementations may call multiple system
924 level "write()"s even if the buffer was empty to start. There may be
925 some systems where this probability is reduced to zero, and this is not
926 a concern when using ":perlio" instead of your system's STDIO.
927 How do I randomly update a binary file?
929 If you're just trying to patch a binary, in many cases something as
930 simple as this works:
931 perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs
933 However, if you have fixed sized records, then you might do something
935 more like this:
936 $RECSIZE = 220; # size of record, in bytes
938 $recno = 37; # which record to update
939 open my $fh, '+<', 'somewhere' or die "can't update somewhere: $!";
940 seek $fh, $recno * $RECSIZE, 0;
941 read $fh, $record, $RECSIZE == $RECSIZE or die "can't read record $recno: $!";
942 # munge the record
943 seek $fh, -$RECSIZE, 1;
944 print $fh $record;
945 close $fh;
946 Locking and error checking are left as an exercise for the reader.
948 Don't forget them or you'll be quite sorry.
949 How do I get a file's timestamp in perl?
951 If you want to retrieve the time at which the file was last read,
952 written, or had its meta-data (owner, etc) changed, you use the -A, -M,
953 or -C file test operations as documented in perlfunc. These retrieve
954 the age of the file (measured against the start-time of your program)
955 in days as a floating point number. Some platforms may not have all of
956 these times. See perlport for details. To retrieve the "raw" time in
957 seconds since the epoch, you would call the stat function, then use
958 "localtime()", "gmtime()", or "POSIX::strftime()" to convert this into
959 human-readable form.
960 Here's an example:
962 my $write_secs = (stat($file))[9];
964 printf "file %s updated at %s\n", $file,
965 scalar localtime($write_secs);
966 If you prefer something more legible, use the File::stat module (part
968 of the standard distribution in version 5.004 and later):
969 # error checking left as an exercise for reader.
971 use File::stat;
972 use Time::localtime;
973 my $date_string = ctime(stat($file)->mtime);
974 print "file $file updated at $date_string\n";
975 The POSIX::strftime() approach has the benefit of being, in theory,
977 independent of the current locale. See perllocale for details.
978 How do I set a file's timestamp in perl?
980 You use the utime() function documented in "utime" in perlfunc. By way
981 of example, here's a little program that copies the read and write
982 times from its first argument to all the rest of them.
983 if (@ARGV < 2) {
985 die "usage: cptimes timestamp_file other_files ...\n";
986 }
987 my $timestamp = shift;
988 my($atime, $mtime) = (stat($timestamp))[8,9];
989 utime $atime, $mtime, @ARGV;
990 Error checking is, as usual, left as an exercise for the reader.
992 The perldoc for utime also has an example that has the same effect as
994 touch(1) on files that already exist.
995 Certain file systems have a limited ability to store the times on a
997 file at the expected level of precision. For example, the FAT and HPFS
998 filesystem are unable to create dates on files with a finer granularity
999 than two seconds. This is a limitation of the filesystems, not of
1000 utime().
1001 How do I print to more than one file at once?
1003 To connect one filehandle to several output filehandles, you can use
1004 the IO::Tee or Tie::FileHandle::Multiplex modules.
1005 If you only have to do this once, you can print individually to each
1007 filehandle.
1008 for my $fh (FH1, FH2, FH3) { print $fh "whatever\n" }
1010 How can I read in an entire file all at once?
1012 Are you sure you want to read the entire file and store it in memory?
1013 If you mmap the file, you can virtually load the entire file into a
1014 string without actually storing it in memory:
1015 use File::Map qw(map_file);
1017 map_file my $string, $filename;
1019 Once mapped, you can treat $string as you would any other string.
1021 Since you don't actually load the data, mmap-ing is very fast and does
1022 not increase your memory footprint.
1023 If you really want to load the entire file, you can use the
1025 "File::Slurp" module to do it in one step.
1026 use File::Slurp;
1028 my $all_of_it = read_file($filename); # entire file in scalar
1030 my @all_lines = read_file($filename); # one line per element
1031 The customary Perl approach for processing all the lines in a file is
1033 to do so one line at a time:
1034 open my $input, '<', $file or die "can't open $file: $!";
1036 while (<$input>) {
1037 chomp;
1038 # do something with $_
1039 }
1040 close $input or die "can't close $file: $!";
1041 This is tremendously more efficient than reading the entire file into
1043 memory as an array of lines and then processing it one element at a
1044 time, which is often--if not almost always--the wrong approach.
1045 Whenever you see someone do this:
1046 my @lines = <INPUT>;
1048 You should think long and hard about why you need everything loaded at
1050 once. It's just not a scalable solution. You might also find it more
1051 fun to use the standard Tie::File module, or the DB_File module's
1052 $DB_RECNO bindings, which allow you to tie an array to a file so that
1053 accessing an element the array actually accesses the corresponding line
1054 in the file.
1055 You can read the entire filehandle contents into a scalar.
1057 {
1059 local $/;
1060 open my $fh, '<', $file or die "can't open $file: $!";
1061 $var = <$fh>;
1062 }
1063 That temporarily undefs your record separator, and will automatically
1065 close the file at block exit. If the file is already open, just use
1066 this:
1067 $var = do { local $/; <$fh> };
1069 For ordinary files you can also use the read function.
1071 read( $fh, $var, -s $fh );
1073 The third argument tests the byte size of the data on the INPUT
1075 filehandle and reads that many bytes into the buffer $var.
1076 How can I read in a file by paragraphs?
1078 Use the $/ variable (see perlvar for details). You can either set it to
1079 "" to eliminate empty paragraphs ("abc\n\n\n\ndef", for instance, gets
1080 treated as two paragraphs and not three), or "\n\n" to accept empty
1081 paragraphs.
1082 Note that a blank line must have no blanks in it. Thus
1084 "fred\n \nstuff\n\n" is one paragraph, but "fred\n\nstuff\n\n" is two.
1085 How can I read a single character from a file? From the keyboard?
1087 You can use the builtin "getc()" function for most filehandles, but it
1088 won't (easily) work on a terminal device. For STDIN, either use the
1089 Term::ReadKey module from CPAN or use the sample code in "getc" in
1090 perlfunc.
1091 If your system supports the portable operating system programming
1093 interface (POSIX), you can use the following code, which you'll note
1094 turns off echo processing as well.
1095 #!/usr/bin/perl -w
1097 use strict;
1098 $| = 1;
1099 for (1..4) {
1100 print "gimme: ";
1101 my $got = getone();
1102 print "--> $got\n";
1103 }
1104 exit;
1105 BEGIN {
1107 use POSIX qw(:termios_h);
1108 my ($term, $oterm, $echo, $noecho, $fd_stdin);
1110 my $fd_stdin = fileno(STDIN);
1112 $term = POSIX::Termios->new();
1114 $term->getattr($fd_stdin);
1115 $oterm = $term->getlflag();
1116 $echo = ECHO | ECHOK | ICANON;
1118 $noecho = $oterm & ~$echo;
1119 sub cbreak {
1121 $term->setlflag($noecho);
1122 $term->setcc(VTIME, 1);
1123 $term->setattr($fd_stdin, TCSANOW);
1124 }
1125 sub cooked {
1127 $term->setlflag($oterm);
1128 $term->setcc(VTIME, 0);
1129 $term->setattr($fd_stdin, TCSANOW);
1130 }
1131 sub getone {
1133 my $key = '';
1134 cbreak();
1135 sysread(STDIN, $key, 1);
1136 cooked();
1137 return $key;
1138 }
1139 }
1141 END { cooked() }
1143 The Term::ReadKey module from CPAN may be easier to use. Recent
1145 versions include also support for non-portable systems as well.
1146 use Term::ReadKey;
1148 open my $tty, '<', '/dev/tty';
1149 print "Gimme a char: ";
1150 ReadMode "raw";
1151 my $key = ReadKey 0, $tty;
1152 ReadMode "normal";
1153 printf "\nYou said %s, char number %03d\n",
1154 $key, ord $key;
1155 How can I tell whether there's a character waiting on a filehandle?
1157 The very first thing you should do is look into getting the
1158 Term::ReadKey extension from CPAN. As we mentioned earlier, it now even
1159 has limited support for non-portable (read: not open systems, closed,
1160 proprietary, not POSIX, not Unix, etc.) systems.
1161 You should also check out the Frequently Asked Questions list in
1163 comp.unix.* for things like this: the answer is essentially the same.
1164 It's very system dependent. Here's one solution that works on BSD
1165 systems:
1166 sub key_ready {
1168 my($rin, $nfd);
1169 vec($rin, fileno(STDIN), 1) = 1;
1170 return $nfd = select($rin,undef,undef,0);
1171 }
1172 If you want to find out how many characters are waiting, there's also
1174 the FIONREAD ioctl call to be looked at. The h2ph tool that comes with
1175 Perl tries to convert C include files to Perl code, which can be
1176 "require"d. FIONREAD ends up defined as a function in the sys/ioctl.ph
1177 file:
1178 require 'sys/ioctl.ph';
1180 $size = pack("L", 0);
1182 ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n";
1183 $size = unpack("L", $size);
1184 If h2ph wasn't installed or doesn't work for you, you can grep the
1186 include files by hand:
1187 % grep FIONREAD /usr/include/*/*
1189 /usr/include/asm/ioctls.h:#define FIONREAD 0x541B
1190 Or write a small C program using the editor of champions:
1192 % cat > fionread.c
1194 #include <sys/ioctl.h>
1195 main() {
1196 printf("%#08x\n", FIONREAD);
1197 }
1198 ^D
1199 % cc -o fionread fionread.c
1200 % ./fionread
1201 0x4004667f
1202 And then hard code it, leaving porting as an exercise to your
1204 successor.
1205 $FIONREAD = 0x4004667f; # XXX: opsys dependent
1207 $size = pack("L", 0);
1209 ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n";
1210 $size = unpack("L", $size);
1211 FIONREAD requires a filehandle connected to a stream, meaning that
1213 sockets, pipes, and tty devices work, but not files.
1214 How do I do a "tail -f" in perl?
1216 First try
1217 seek(GWFILE, 0, 1);
1219 The statement "seek(GWFILE, 0, 1)" doesn't change the current position,
1221 but it does clear the end-of-file condition on the handle, so that the
1222 next "<GWFILE>" makes Perl try again to read something.
1223 If that doesn't work (it relies on features of your stdio
1225 implementation), then you need something more like this:
1226 for (;;) {
1228 for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE)) {
1229 # search for some stuff and put it into files
1230 }
1231 # sleep for a while
1232 seek(GWFILE, $curpos, 0); # seek to where we had been
1233 }
1234 If this still doesn't work, look into the "clearerr" method from
1236 "IO::Handle", which resets the error and end-of-file states on the
1237 handle.
1238 There's also a "File::Tail" module from CPAN.
1240 How do I dup() a filehandle in Perl?
1242 If you check "open" in perlfunc, you'll see that several of the ways to
1243 call open() should do the trick. For example:
1244 open my $log, '>>', '/foo/logfile';
1246 open STDERR, '>&LOG';
1247 Or even with a literal numeric descriptor:
1249 my $fd = $ENV{MHCONTEXTFD};
1251 open $mhcontext, "<&=$fd"; # like fdopen(3S)
1252 Note that "<&STDIN" makes a copy, but "<&=STDIN" make an alias. That
1254 means if you close an aliased handle, all aliases become inaccessible.
1255 This is not true with a copied one.
1256 Error checking, as always, has been left as an exercise for the reader.
1258 How do I close a file descriptor by number?
1260 If, for some reason, you have a file descriptor instead of a filehandle
1261 (perhaps you used "POSIX::open"), you can use the "close()" function
1262 from the "POSIX" module:
1263 use POSIX ();
1265 POSIX::close( $fd );
1267 This should rarely be necessary, as the Perl "close()" function is to
1269 be used for things that Perl opened itself, even if it was a dup of a
1270 numeric descriptor as with "MHCONTEXT" above. But if you really have
1271 to, you may be able to do this:
1272 require 'sys/syscall.ph';
1274 my $rc = syscall(&SYS_close, $fd + 0); # must force numeric
1275 die "can't sysclose $fd: $!" unless $rc == -1;
1276 Or, just use the fdopen(3S) feature of "open()":
1278 {
1280 open my( $fh ), "<&=$fd" or die "Cannot reopen fd=$fd: $!";
1281 close $fh;
1282 }
1283 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe`
1285 work?
1286 Whoops! You just put a tab and a formfeed into that filename!
1287 Remember that within double quoted strings ("like\this"), the backslash
1288 is an escape character. The full list of these is in "Quote and Quote-
1289 like Operators" in perlop. Unsurprisingly, you don't have a file called
1290 "c:(tab)emp(formfeed)oo" or "c:(tab)emp(formfeed)oo.exe" on your legacy
1291 DOS filesystem.
1292 Either single-quote your strings, or (preferably) use forward slashes.
1294 Since all DOS and Windows versions since something like MS-DOS 2.0 or
1295 so have treated "/" and "\" the same in a path, you might as well use
1296 the one that doesn't clash with Perl--or the POSIX shell, ANSI C and
1297 C++, awk, Tcl, Java, or Python, just to mention a few. POSIX paths are
1298 more portable, too.
1299 Why doesn't glob("*.*") get all the files?
1301 Because even on non-Unix ports, Perl's glob function follows standard
1302 Unix globbing semantics. You'll need "glob("*")" to get all (non-
1303 hidden) files. This makes glob() portable even to legacy systems. Your
1304 port may include proprietary globbing functions as well. Check its
1305 documentation for details.
1306 Why does Perl let me delete read-only files? Why does "-i" clobber
1308 protected files? Isn't this a bug in Perl?
1309 This is elaborately and painstakingly described in the file-dir-perms
1310 article in the "Far More Than You Ever Wanted To Know" collection in
1311 http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz .
1312 The executive summary: learn how your filesystem works. The permissions
1314 on a file say what can happen to the data in that file. The
1315 permissions on a directory say what can happen to the list of files in
1316 that directory. If you delete a file, you're removing its name from the
1317 directory (so the operation depends on the permissions of the
1318 directory, not of the file). If you try to write to the file, the
1319 permissions of the file govern whether you're allowed to.
1320 How do I select a random line from a file?
1322 Short of loading the file into a database or pre-indexing the lines in
1323 the file, there are a couple of things that you can do.
1324 Here's a reservoir-sampling algorithm from the Camel Book:
1326 srand;
1328 rand($.) < 1 && ($line = $_) while <>;
1329 This has a significant advantage in space over reading the whole file
1331 in. You can find a proof of this method in The Art of Computer
1332 Programming, Volume 2, Section 3.4.2, by Donald E. Knuth.
1333 You can use the "File::Random" module which provides a function for
1335 that algorithm:
1336 use File::Random qw/random_line/;
1338 my $line = random_line($filename);
1339 Another way is to use the "Tie::File" module, which treats the entire
1341 file as an array. Simply access a random array element.
1342 Why do I get weird spaces when I print an array of lines?
1344 (contributed by brian d foy)
1345 If you are seeing spaces between the elements of your array when you
1347 print the array, you are probably interpolating the array in double
1348 quotes:
1349 my @animals = qw(camel llama alpaca vicuna);
1351 print "animals are: @animals\n";
1352 It's the double quotes, not the "print", doing this. Whenever you
1354 interpolate an array in a double quote context, Perl joins the elements
1355 with spaces (or whatever is in $", which is a space by default):
1356 animals are: camel llama alpaca vicuna
1358 This is different than printing the array without the interpolation:
1360 my @animals = qw(camel llama alpaca vicuna);
1362 print "animals are: ", @animals, "\n";
1363 Now the output doesn't have the spaces between the elements because the
1365 elements of @animals simply become part of the list to "print":
1366 animals are: camelllamaalpacavicuna
1368 You might notice this when each of the elements of @array end with a
1370 newline. You expect to print one element per line, but notice that
1371 every line after the first is indented:
1372 this is a line
1374 this is another line
1375 this is the third line
1376 That extra space comes from the interpolation of the array. If you
1378 don't want to put anything between your array elements, don't use the
1379 array in double quotes. You can send it to print without them:
1380 print @lines;
1382 How do I traverse a directory tree?
1384 (contributed by brian d foy)
1385 The "File::Find" module, which comes with Perl, does all of the hard
1387 work to traverse a directory structure. It comes with Perl. You simply
1388 call the "find" subroutine with a callback subroutine and the
1389 directories you want to traverse:
1390 use File::Find;
1392 find( \&wanted, @directories );
1394 sub wanted {
1396 # full path in $File::Find::name
1397 # just filename in $_
1398 ... do whatever you want to do ...
1399 }
1400 The "File::Find::Closures", which you can download from CPAN, provides
1402 many ready-to-use subroutines that you can use with "File::Find".
1403 The "File::Finder", which you can download from CPAN, can help you
1405 create the callback subroutine using something closer to the syntax of
1406 the "find" command-line utility:
1407 use File::Find;
1409 use File::Finder;
1410 my $deep_dirs = File::Finder->depth->type('d')->ls->exec('rmdir','{}');
1412 find( $deep_dirs->as_options, @places );
1414 The "File::Find::Rule" module, which you can download from CPAN, has a
1416 similar interface, but does the traversal for you too:
1417 use File::Find::Rule;
1419 my @files = File::Find::Rule->file()
1421 ->name( '*.pm' )
1422 ->in( @INC );
1423 How do I delete a directory tree?
1425 (contributed by brian d foy)
1426 If you have an empty directory, you can use Perl's built-in "rmdir".
1428 If the directory is not empty (so, no files or subdirectories), you
1429 either have to empty it yourself (a lot of work) or use a module to
1430 help you.
1431 The "File::Path" module, which comes with Perl, has a "remove_tree"
1433 which can take care of all of the hard work for you:
1434 use File::Path qw(remove_tree);
1436 remove_tree( @directories );
1438 The "File::Path" module also has a legacy interface to the older
1440 "rmtree" subroutine.
1441 How do I copy an entire directory?
1443 (contributed by Shlomi Fish)
1444 To do the equivalent of "cp -R" (i.e. copy an entire directory tree
1446 recursively) in portable Perl, you'll either need to write something
1447 yourself or find a good CPAN module such as File::Copy::Recursive.
1448
1450 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and other
1451 authors as noted. All rights reserved.
1452 This documentation is free; you can redistribute it and/or modify it
1454 under the same terms as Perl itself.
1455 Irrespective of its distribution, all code examples here are in the
1457 public domain. You are permitted and encouraged to use this code and
1458 any derivatives thereof in your own programs for fun or for profit as
1459 you see fit. A simple comment in the code giving credit to the FAQ
1460 would be courteous but is not required.
1461perl v5.12.4 2011-06-07 PERLFAQ5(1)