3 perlfaq5 - Files and Formats
7 This section deals with I/O and the "f" issues: filehandles, flushing,
10 =head2 How do I flush/unbuffer an output filehandle? Why must I do this?
11 X<flush> X<buffer> X<unbuffer> X<autoflush>
13 (contributed by brian d foy)
15 You might like to read Mark Jason Dominus's "Suffering From Buffering"
16 at http://perl.plover.com/FAQs/Buffering.html .
18 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 calls.
20 For instance, in this little bit of code, you want to print a dot to the
21 screen for every line you process to watch the progress of your program.
22 Instead of seeing a dot for every line, Perl buffers the output and you
23 have a long wait before you see a row of 50 dots all at once:
25 # long wait, then row of dots all at once
28 print "\n" unless ++$count % 50;
30 #... expensive line processing operations
33 To get around this, you have to unbuffer the output filehandle, in this
34 case, C<STDOUT>. You can set the special variable C<$|> to a true value
35 (mnemonic: making your filehandles "piping hot"):
39 # dot shown immediately
42 print "\n" unless ++$count % 50;
44 #... expensive line processing operations
47 The C<$|> is one of the per-filehandle special variables, so each
48 filehandle has its own copy of its value. If you want to merge
49 standard output and standard error for instance, you have to unbuffer
50 each (although STDERR might be unbuffered by default):
53 my $previous_default = select(STDOUT); # save previous default
54 $|++; # autoflush STDOUT
56 $|++; # autoflush STDERR, to be sure
57 select($previous_default); # restore previous default
60 # now should alternate . and +
66 print STDOUT "\n" unless ++$count % 25;
69 Besides the C<$|> special variable, you can use C<binmode> to give
70 your filehandle a C<:unix> layer, which is unbuffered:
72 binmode( STDOUT, ":unix" );
77 print "\n" unless ++$count % 50;
80 For more information on output layers, see the entries for C<binmode>
81 and C<open> in L<perlfunc>, and the C<PerlIO> module documentation.
83 If you are using C<IO::Handle> or one of its subclasses, you can
84 call the C<autoflush> method to change the settings of the
88 open my( $io_fh ), ">", "output.txt";
91 The C<IO::Handle> objects also have a C<flush> method. You can flush
92 the buffer any time you want without auto-buffering
96 =head2 How do I change, delete, or insert a line in a file, or append to the beginning of a file?
99 (contributed by brian d foy)
101 The basic idea of inserting, changing, or deleting a line from a text
102 file involves reading and printing the file to the point you want to
103 make the change, making the change, then reading and printing the rest
104 of the file. Perl doesn't provide random access to lines (especially
105 since the record input separator, C<$/>, is mutable), although modules
106 such as C<Tie::File> can fake it.
108 A Perl program to do these tasks takes the basic form of opening a
109 file, printing its lines, then closing the file:
111 open my $in, '<', $file or die "Can't read old file: $!";
112 open my $out, '>', "$file.new" or die "Can't write new file: $!";
121 Within that basic form, add the parts that you need to insert, change,
124 To prepend lines to the beginning, print those lines before you enter
125 the loop that prints the existing lines.
127 open my $in, '<', $file or die "Can't read old file: $!";
128 open my $out, '>', "$file.new" or die "Can't write new file: $!";
130 print $out "# Add this line to the top\n"; # <--- HERE'S THE MAGIC
139 To change existing lines, insert the code to modify the lines inside
140 the C<while> loop. In this case, the code finds all lowercased
141 versions of "perl" and uppercases them. The happens for every line, so
142 be sure that you're supposed to do that on every line!
144 open my $in, '<', $file or die "Can't read old file: $!";
145 open my $out, '>', "$file.new" or die "Can't write new file: $!";
147 print $out "# Add this line to the top\n";
157 To change only a particular line, the input line number, C<$.>, is
158 useful. First read and print the lines up to the one you want to
159 change. Next, read the single line you want to change, change it, and
160 print it. After that, read the rest of the lines and print those:
162 while( <$in> ) # print the lines before the change
165 last if $. == 4; # line number before change
169 $line =~ s/\b(perl)\b/Perl/g;
172 while( <$in> ) # print the rest of the lines
177 To skip lines, use the looping controls. The C<next> in this example
178 skips comment lines, and the C<last> stops all processing once it
179 encounters either C<__END__> or C<__DATA__>.
183 next if /^\s+#/; # skip comment lines
184 last if /^__(END|DATA)__$/; # stop at end of code marker
188 Do the same sort of thing to delete a particular line by using C<next>
189 to skip the lines you don't want to show up in the output. This
190 example skips every fifth line:
198 If, for some odd reason, you really want to see the whole file at once
199 rather than processing line-by-line, you can slurp it in (as long as
200 you can fit the whole thing in memory!):
202 open my $in, '<', $file or die "Can't read old file: $!"
203 open my $out, '>', "$file.new" or die "Can't write new file: $!";
205 my @lines = do { local $/; <$in> }; # slurp!
211 Modules such as C<File::Slurp> and C<Tie::File> can help with that
212 too. If you can, however, avoid reading the entire file at once. Perl
213 won't give that memory back to the operating system until the process
216 You can also use Perl one-liners to modify a file in-place. The
217 following changes all 'Fred' to 'Barney' in F<inFile.txt>, overwriting
218 the file with the new contents. With the C<-p> switch, Perl wraps a
219 C<while> loop around the code you specify with C<-e>, and C<-i> turns
220 on in-place editing. The current line is in C<$_>. With C<-p>, Perl
221 automatically prints the value of C<$_> at the end of the loop. See
222 L<perlrun> for more details.
224 perl -pi -e 's/Fred/Barney/' inFile.txt
226 To make a backup of C<inFile.txt>, give C<-i> a file extension to add:
228 perl -pi.bak -e 's/Fred/Barney/' inFile.txt
230 To change only the fifth line, you can add a test checking C<$.>, the
231 input line number, then only perform the operation when the test
234 perl -pi -e 's/Fred/Barney/ if $. == 5' inFile.txt
236 To add lines before a certain line, you can add a line (or lines!)
237 before Perl prints C<$_>:
239 perl -pi -e 'print "Put before third line\n" if $. == 3' inFile.txt
241 You can even add a line to the beginning of a file, since the current
242 line prints at the end of the loop:
244 perl -pi -e 'print "Put before first line\n" if $. == 1' inFile.txt
246 To insert a line after one already in the file, use the C<-n> switch.
247 It's just like C<-p> except that it doesn't print C<$_> at the end of
248 the loop, so you have to do that yourself. In this case, print C<$_>
249 first, then print the line that you want to add.
251 perl -ni -e 'print; print "Put after fifth line\n" if $. == 5' inFile.txt
253 To delete lines, only print the ones that you want.
255 perl -ni -e 'print unless /d/' inFile.txt
259 perl -pi -e 'next unless /d/' inFile.txt
261 =head2 How do I count the number of lines in a file?
262 X<file, counting lines> X<lines> X<line>
264 (contributed by brian d foy)
266 Conceptually, the easiest way to count the lines in a file is to
267 simply read them and count them:
270 while( <$fh> ) { $count++; }
272 You don't really have to count them yourself, though, since Perl
273 already does that with the C<$.> variable, which is the current line
274 number from the last filehandle read:
279 If you want to use C<$.>, you can reduce it to a simple one-liner,
282 % perl -lne '} print $.; {' file
284 % perl -lne 'END { print $. }' file
286 Those can be rather inefficient though. If they aren't fast enough for
287 you, you might just read chunks of data and count the number of
291 open my($fh), '<:raw', $filename or die "Can't open $filename: $!";
292 while( sysread $fh, $buffer, 4096 ) {
293 $lines += ( $buffer =~ tr/\n// );
297 However, that doesn't work if the line ending isn't a newline. You
298 might change that C<tr///> to a C<s///> so you can count the number of
299 times the input record separator, C<$/>, shows up:
302 open my($fh), '<:raw', $filename or die "Can't open $filename: $!";
303 while( sysread $fh, $buffer, 4096 ) {
304 $lines += ( $buffer =~ s|$/||g; );
308 If you don't mind shelling out, the C<wc> command is usually the
309 fastest, even with the extra interprocess overhead. Ensure that you
310 have an untainted filename though:
317 if( $filename =~ /^([0-9a-z_.]+)\z/ ) {
318 $lines = `/usr/bin/wc -l $1`
322 =head2 How do I delete the last N lines from a file?
325 (contributed by brian d foy)
327 The easiest conceptual solution is to count the lines in the
328 file then start at the beginning and print the number of lines
329 (minus the last N) to a new file.
331 Most often, the real question is how you can delete the last N lines
332 without making more than one pass over the file, or how to do it
333 without a lot of copying. The easy concept is the hard reality when
334 you might have millions of lines in your file.
336 One trick is to use C<File::ReadBackwards>, which starts at the end of
337 the file. That module provides an object that wraps the real filehandle
338 to make it easy for you to move around the file. Once you get to the
339 spot you need, you can get the actual filehandle and work with it as
340 normal. In this case, you get the file position at the end of the last
341 line you want to keep and truncate the file to that point:
343 use File::ReadBackwards;
345 my $filename = 'test.txt';
346 my $Lines_to_truncate = 2;
348 my $bw = File::ReadBackwards->new( $filename )
349 or die "Could not read backwards in [$filename]: $!";
351 my $lines_from_end = 0;
352 until( $bw->eof or $lines_from_end == $Lines_to_truncate )
354 print "Got: ", $bw->readline;
358 truncate( $filename, $bw->tell );
360 The C<File::ReadBackwards> module also has the advantage of setting
361 the input record separator to a regular expression.
363 You can also use the C<Tie::File> module which lets you access
364 the lines through a tied array. You can use normal array operations
365 to modify your file, including setting the last index and using
368 =head2 How can I use Perl's C<-i> option from within a program?
371 C<-i> sets the value of Perl's C<$^I> variable, which in turn affects
372 the behavior of C<< <> >>; see L<perlrun> for more details. By
373 modifying the appropriate variables directly, you can get the same
374 behavior within a larger program. For example:
378 local($^I, @ARGV) = ('.orig', glob("*.c"));
381 print "This line should appear at the top of each file\n";
383 s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case
385 close ARGV if eof; # Reset $.
388 # $^I and @ARGV return to their old values here
390 This block modifies all the C<.c> files in the current directory,
391 leaving a backup of the original data from each file in a new
394 =head2 How can I copy a file?
395 X<copy> X<file, copy> X<File::Copy>
397 (contributed by brian d foy)
399 Use the C<File::Copy> module. It comes with Perl and can do a
400 true copy across file systems, and it does its magic in
405 copy( $original, $new_copy ) or die "Copy failed: $!";
407 If you can't use C<File::Copy>, you'll have to do the work yourself:
408 open the original file, open the destination file, then print
409 to the destination file as you read the original. You also have to
410 remember to copy the permissions, owner, and group to the new file.
412 =head2 How do I make a temporary file name?
415 If you don't need to know the name of the file, you can use C<open()>
416 with C<undef> in place of the file name. In Perl 5.8 or later, the
417 C<open()> function creates an anonymous temporary file:
419 open my $tmp, '+>', undef or die $!;
421 Otherwise, you can use the File::Temp module.
423 use File::Temp qw/ tempfile tempdir /;
425 my $dir = tempdir( CLEANUP => 1 );
426 ($fh, $filename) = tempfile( DIR => $dir );
428 # or if you don't need to know the filename
430 my $fh = tempfile( DIR => $dir );
432 The File::Temp has been a standard module since Perl 5.6.1. If you
433 don't have a modern enough Perl installed, use the C<new_tmpfile>
434 class method from the IO::File module to get a filehandle opened for
435 reading and writing. Use it if you don't need to know the file's name:
438 my $fh = IO::File->new_tmpfile()
439 or die "Unable to make new temporary file: $!";
441 If you're committed to creating a temporary file by hand, use the
442 process ID and/or the current time-value. If you need to have many
443 temporary files in one process, use a counter:
447 my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMPDIR} || $ENV{TEMP};
448 my $base_name = sprintf "%s/%d-%d-0000", $temp_dir, $$, time;
453 until( defined(fileno($fh)) || $count++ > 100 ) {
454 $base_name =~ s/-(\d+)$/"-" . (1 + $1)/e;
455 # O_EXCL is required for security reasons.
456 sysopen $fh, $base_name, O_WRONLY|O_EXCL|O_CREAT;
459 if( defined fileno($fh) ) {
460 return ($fh, $base_name);
469 =head2 How can I manipulate fixed-record-length files?
470 X<fixed-length> X<file, fixed-length records>
472 The most efficient way is using L<pack()|perlfunc/"pack"> and
473 L<unpack()|perlfunc/"unpack">. This is faster than using
474 L<substr()|perlfunc/"substr"> when taking many, many strings. It is
475 slower for just a few.
477 Here is a sample chunk of code to break up and put back together again
478 some fixed-format input lines, in this case from the output of a normal,
482 # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what
483 my $PS_T = 'A6 A4 A7 A5 A*';
484 open my $ps, '-|', 'ps';
486 my @fields = qw( pid tt stat time command );
489 @process{@fields} = unpack($PS_T, $_);
490 for my $field ( @fields ) {
491 print "$field: <$process{$field}>\n";
493 print 'line=', pack($PS_T, @process{@fields} ), "\n";
496 We've used a hash slice in order to easily handle the fields of each row.
497 Storing the keys in an array means it's easy to operate on them as a
498 group or loop over them with for. It also avoids polluting the program
499 with global variables and using symbolic references.
501 =head2 How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?
502 X<filehandle, local> X<filehandle, passing> X<filehandle, reference>
504 As of perl5.6, open() autovivifies file and directory handles
505 as references if you pass it an uninitialized scalar variable.
506 You can then pass these references just like any other scalar,
507 and use them in the place of named handles.
509 open my $fh, $file_name;
511 open local $fh, $file_name;
513 print $fh "Hello World!\n";
517 If you like, you can store these filehandles in an array or a hash.
518 If you access them directly, they aren't simple scalars and you
519 need to give C<print> a little help by placing the filehandle
520 reference in braces. Perl can only figure it out on its own when
521 the filehandle reference is a simple scalar.
523 my @fhs = ( $fh1, $fh2, $fh3 );
525 for( $i = 0; $i <= $#fhs; $i++ ) {
526 print {$fhs[$i]} "just another Perl answer, \n";
529 Before perl5.6, you had to deal with various typeglob idioms
530 which you may see in older code.
532 open FILE, "> $filename";
533 process_typeglob( *FILE );
534 process_reference( \*FILE );
536 sub process_typeglob { local *FH = shift; print FH "Typeglob!" }
537 sub process_reference { local $fh = shift; print $fh "Reference!" }
539 If you want to create many anonymous handles, you should
540 check out the Symbol or IO::Handle modules.
542 =head2 How can I use a filehandle indirectly?
543 X<filehandle, indirect>
545 An indirect filehandle is using something other than a symbol
546 in a place that a filehandle is expected. Here are ways
547 to get indirect filehandles:
549 $fh = SOME_FH; # bareword is strict-subs hostile
550 $fh = "SOME_FH"; # strict-refs hostile; same package only
551 $fh = *SOME_FH; # typeglob
552 $fh = \*SOME_FH; # ref to typeglob (bless-able)
553 $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob
555 Or, you can use the C<new> method from one of the IO::* modules to
556 create an anonymous filehandle, store that in a scalar variable,
557 and use it as though it were a normal filehandle.
559 use IO::Handle; # 5.004 or higher
560 my $fh = IO::Handle->new();
562 Then use any of those as you would a normal filehandle. Anywhere that
563 Perl is expecting a filehandle, an indirect filehandle may be used
564 instead. An indirect filehandle is just a scalar variable that contains
565 a filehandle. Functions like C<print>, C<open>, C<seek>, or
566 the C<< <FH> >> diamond operator will accept either a named filehandle
567 or a scalar variable containing one:
569 ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR);
570 print $ofh "Type it: ";
572 print $efh "What was that: $got";
574 If you're passing a filehandle to a function, you can write
575 the function in two ways:
579 print $fh "Sending to indirect filehandle\n";
582 Or it can localize a typeglob and use the filehandle directly:
586 print FH "Sending to localized filehandle\n";
589 Both styles work with either objects or typeglobs of real filehandles.
590 (They might also work with strings under some circumstances, but this
596 In the examples above, we assigned the filehandle to a scalar variable
597 before using it. That is because only simple scalar variables, not
598 expressions or subscripts of hashes or arrays, can be used with
599 built-ins like C<print>, C<printf>, or the diamond operator. Using
600 something other than a simple scalar variable as a filehandle is
601 illegal and won't even compile:
603 my @fd = (*STDIN, *STDOUT, *STDERR);
604 print $fd[1] "Type it: "; # WRONG
605 my $got = <$fd[0]> # WRONG
606 print $fd[2] "What was that: $got"; # WRONG
608 With C<print> and C<printf>, you get around this by using a block and
609 an expression where you would place the filehandle:
611 print { $fd[1] } "funny stuff\n";
612 printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559;
613 # Pity the poor deadbeef.
615 That block is a proper block like any other, so you can put more
616 complicated code there. This sends the message out to one of two places:
618 my $ok = -x "/bin/cat";
619 print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n";
620 print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n";
622 This approach of treating C<print> and C<printf> like object methods
623 calls doesn't work for the diamond operator. That's because it's a
624 real operator, not just a function with a comma-less argument. Assuming
625 you've been storing typeglobs in your structure as we did above, you
626 can use the built-in function named C<readline> to read a record just
627 as C<< <> >> does. Given the initialization shown above for @fd, this
628 would work, but only because readline() requires a typeglob. It doesn't
629 work with objects or strings, which might be a bug we haven't fixed yet.
631 $got = readline($fd[0]);
633 Let it be noted that the flakiness of indirect filehandles is not
634 related to whether they're strings, typeglobs, objects, or anything else.
635 It's the syntax of the fundamental operators. Playing the object
636 game doesn't help you at all here.
638 =head2 How can I set up a footer format to be used with write()?
641 There's no builtin way to do this, but L<perlform> has a couple of
642 techniques to make it possible for the intrepid hacker.
644 =head2 How can I write() into a string?
645 X<write, into a string>
647 (contributed by brian d foy)
649 If you want to C<write> into a string, you just have to <open> a
650 filehandle to a string, which Perl has been able to do since Perl 5.6:
652 open FH, '>', \my $string;
655 Since you want to be a good programmer, you probably want to use a lexical
656 filehandle, even though formats are designed to work with bareword filehandles
657 since the default format names take the filehandle name. However, you can
658 control this with some Perl special per-filehandle variables: C<$^>, which
659 names the top-of-page format, and C<$~> which shows the line format. You have
660 to change the default filehandle to set these variables:
662 open my($fh), '>', \my $string;
664 { # set per-filehandle variables
665 my $old_fh = select( $fh );
676 @## @<<< @<<<<<<<<<<<<<<
680 Although write can work with lexical or package variables, whatever variables
681 you use have to scope in the format. That most likely means you'll want to
682 localize some package variables:
685 local( $id, $type, $name ) = qw( 12 cat Buster );
691 There are also some tricks that you can play with C<formline> and the
692 accumulator variable C<$^A>, but you lose a lot of the value of formats
693 since C<formline> won't handle paging and so on. You end up reimplementing
694 formats when you use them.
696 =head2 How can I open a filehandle to a string?
697 X<string> X<open> X<IO::String> X<filehandle>
699 (contributed by Peter J. Holzer, hjp-usenet2@hjp.at)
701 Since Perl 5.8.0 a file handle referring to a string can be created by
702 calling open with a reference to that string instead of the filename.
703 This file handle can then be used to read from or write to the string:
705 open(my $fh, '>', \$string) or die "Could not open string for writing";
707 print $fh "bar\n"; # $string now contains "foo\nbar\n"
709 open(my $fh, '<', \$string) or die "Could not open string for reading";
710 my $x = <$fh>; # $x now contains "foo\n"
712 With older versions of Perl, the C<IO::String> module provides similar
715 =head2 How can I output my numbers with commas added?
718 (contributed by brian d foy and Benjamin Goldberg)
720 You can use L<Number::Format> to separate places in a number.
721 It handles locale information for those of you who want to insert
722 full stops instead (or anything else that they want to use,
725 This subroutine will add commas to your number:
729 1 while s/^([-+]?\d+)(\d{3})/$1,$2/;
733 This regex from Benjamin Goldberg will add commas to numbers:
735 s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g;
737 It is easier to see with comments:
740 ^[-+]? # beginning of number.
741 \d+? # first digits before first comma
742 (?= # followed by, (but not included in the match) :
743 (?>(?:\d{3})+) # some positive multiple of three digits.
744 (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever.
747 \G\d{3} # after the last group, get three digits
748 (?=\d) # but they have to have more digits after them.
751 =head2 How can I translate tildes (~) in a filename?
752 X<tilde> X<tilde expansion>
754 Use the E<lt>E<gt> (C<glob()>) operator, documented in L<perlfunc>.
755 Versions of Perl older than 5.6 require that you have a shell
756 installed that groks tildes. Later versions of Perl have this feature
757 built in. The C<File::KGlob> module (available from CPAN) gives more
758 portable glob functionality.
760 Within Perl, you may use this directly:
763 ^ ~ # find a leading tilde
765 [^/] # a non-slash character
766 * # repeated 0 or more times (0 means me)
771 : ( $ENV{HOME} || $ENV{LOGDIR} )
774 =head2 How come when I open a file read-write it wipes it out?
775 X<clobber> X<read-write> X<clobbering> X<truncate> X<truncating>
777 Because you're using something like this, which truncates the file
778 I<then> gives you read-write access:
780 open my $fh, '+>', '/path/name'; # WRONG (almost always)
782 Whoops. You should instead use this, which will fail if the file
785 open my $fh, '+<', '/path/name'; # open for update
787 Using ">" always clobbers or creates. Using "<" never does
788 either. The "+" doesn't change this.
790 Here are examples of many kinds of file opens. Those using C<sysopen>
791 all assume that you've pulled in the constants from C<Fcntl>:
795 To open file for reading:
797 open my $fh, '<', $path or die $!;
798 sysopen my $fh, $path, O_RDONLY or die $!;
800 To open file for writing, create new file if needed or else truncate old file:
802 open my $fh, '>', $path or die $!;
803 sysopen my $fh, $path, O_WRONLY|O_TRUNC|O_CREAT or die $!;
804 sysopen my $fh, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666 or die $!;
806 To open file for writing, create new file, file must not exist:
808 sysopen my $fh, $path, O_WRONLY|O_EXCL|O_CREAT or die $!;
809 sysopen my $fh, $path, O_WRONLY|O_EXCL|O_CREAT, 0666 or die $!;
811 To open file for appending, create if necessary:
813 open my $fh, '>>' $path or die $!;
814 sysopen my $fh, $path, O_WRONLY|O_APPEND|O_CREAT or die $!;
815 sysopen my $fh, $path, O_WRONLY|O_APPEND|O_CREAT, 0666 or die $!;
817 To open file for appending, file must exist:
819 sysopen my $fh, $path, O_WRONLY|O_APPEND or die $!;
821 To open file for update, file must exist:
823 open my $fh, '+<', $path or die $!;
824 sysopen my $fh, $path, O_RDWR or die $!;
826 To open file for update, create file if necessary:
828 sysopen my $fh, $path, O_RDWR|O_CREAT or die $!;
829 sysopen my $fh, $path, O_RDWR|O_CREAT, 0666 or die $!;
831 To open file for update, file must not exist:
833 sysopen my $fh, $path, O_RDWR|O_EXCL|O_CREAT or die $!;
834 sysopen my $fh, $path, O_RDWR|O_EXCL|O_CREAT, 0666 or die $!;
836 To open a file without blocking, creating if necessary:
838 sysopen my $fh, '/foo/somefile', O_WRONLY|O_NDELAY|O_CREAT
839 or die "can't open /foo/somefile: $!":
841 Be warned that neither creation nor deletion of files is guaranteed to
842 be an atomic operation over NFS. That is, two processes might both
843 successfully create or unlink the same file! Therefore O_EXCL
844 isn't as exclusive as you might wish.
846 See also the new L<perlopentut>.
848 =head2 Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
849 X<argument list too long>
851 The C<< <> >> operator performs a globbing operation (see above).
852 In Perl versions earlier than v5.6.0, the internal glob() operator forks
853 csh(1) to do the actual glob expansion, but
854 csh can't handle more than 127 items and so gives the error message
855 C<Argument list too long>. People who installed tcsh as csh won't
856 have this problem, but their users may be surprised by it.
858 To get around this, either upgrade to Perl v5.6.0 or later, do the glob
859 yourself with readdir() and patterns, or use a module like File::KGlob,
860 one that doesn't use the shell to do globbing.
862 =head2 Is there a leak/bug in glob()?
865 (contributed by brian d foy)
867 Starting with Perl 5.6.0, C<glob> is implemented internally rather
868 than relying on an external resource. As such, memory issues with
869 C<glob> aren't a problem in modern perls.
871 =head2 How can I open a file with a leading ">" or trailing blanks?
872 X<filename, special characters>
874 (contributed by Brian McCauley)
876 The special two argument form of Perl's open() function ignores
877 trailing blanks in filenames and infers the mode from certain leading
878 characters (or a trailing "|"). In older versions of Perl this was the
879 only version of open() and so it is prevalent in old code and books.
881 Unless you have a particular reason to use the two argument form you
882 should use the three argument form of open() which does not treat any
883 characters in the filename as special.
885 open my $fh, "<", " file "; # filename is " file "
886 open my $fh, ">", ">file"; # filename is ">file"
888 =head2 How can I reliably rename a file?
889 X<rename> X<mv> X<move> X<file, rename>
891 If your operating system supports a proper mv(1) utility or its
892 functional equivalent, this works:
894 rename($old, $new) or system("mv", $old, $new);
896 It may be more portable to use the C<File::Copy> module instead.
897 You just copy to the new file to the new name (checking return
898 values), then delete the old one. This isn't really the same
899 semantically as a C<rename()>, which preserves meta-information like
900 permissions, timestamps, inode info, etc.
902 =head2 How can I lock a file?
903 X<lock> X<file, lock> X<flock>
905 Perl's builtin flock() function (see L<perlfunc> for details) will call
906 flock(2) if that exists, fcntl(2) if it doesn't (on perl version 5.004 and
907 later), and lockf(3) if neither of the two previous system calls exists.
908 On some systems, it may even use a different form of native locking.
909 Here are some gotchas with Perl's flock():
915 Produces a fatal error if none of the three system calls (or their
916 close equivalent) exists.
920 lockf(3) does not provide shared locking, and requires that the
921 filehandle be open for writing (or appending, or read/writing).
925 Some versions of flock() can't lock files over a network (e.g. on NFS file
926 systems), so you'd need to force the use of fcntl(2) when you build Perl.
927 But even this is dubious at best. See the flock entry of L<perlfunc>
928 and the F<INSTALL> file in the source distribution for information on
929 building Perl to do this.
931 Two potentially non-obvious but traditional flock semantics are that
932 it waits indefinitely until the lock is granted, and that its locks are
933 I<merely advisory>. Such discretionary locks are more flexible, but
934 offer fewer guarantees. This means that files locked with flock() may
935 be modified by programs that do not also use flock(). Cars that stop
936 for red lights get on well with each other, but not with cars that don't
937 stop for red lights. See the perlport manpage, your port's specific
938 documentation, or your system-specific local manpages for details. It's
939 best to assume traditional behavior if you're writing portable programs.
940 (If you're not, you should as always feel perfectly free to write
941 for your own system's idiosyncrasies (sometimes called "features").
942 Slavish adherence to portability concerns shouldn't get in the way of
943 your getting your job done.)
945 For more information on file locking, see also
946 L<perlopentut/"File Locking"> if you have it (new for 5.6).
950 =head2 Why can't I just open(FH, "E<gt>file.lock")?
951 X<lock, lockfile race condition>
953 A common bit of code B<NOT TO USE> is this:
955 sleep(3) while -e 'file.lock'; # PLEASE DO NOT USE
956 open my $lock, '>', 'file.lock'; # THIS BROKEN CODE
958 This is a classic race condition: you take two steps to do something
959 which must be done in one. That's why computer hardware provides an
960 atomic test-and-set instruction. In theory, this "ought" to work:
962 sysopen my $fh, "file.lock", O_WRONLY|O_EXCL|O_CREAT
963 or die "can't open file.lock: $!";
965 except that lamentably, file creation (and deletion) is not atomic
966 over NFS, so this won't work (at least, not every time) over the net.
967 Various schemes involving link() have been suggested, but
968 these tend to involve busy-wait, which is also less than desirable.
970 =head2 I still don't get locking. I just want to increment the number in the file. How can I do this?
971 X<counter> X<file, counter>
973 Didn't anyone ever tell you web-page hit counters were useless?
974 They don't count number of hits, they're a waste of time, and they serve
975 only to stroke the writer's vanity. It's better to pick a random number;
976 they're more realistic.
978 Anyway, this is what you can do if you can't help yourself.
980 use Fcntl qw(:DEFAULT :flock);
981 sysopen my $fh, "numfile", O_RDWR|O_CREAT or die "can't open numfile: $!";
982 flock $fh, LOCK_EX or die "can't flock numfile: $!";
983 my $num = <$fh> || 0;
984 seek $fh, 0, 0 or die "can't rewind numfile: $!";
985 truncate $fh, 0 or die "can't truncate numfile: $!";
986 (print $fh $num+1, "\n") or die "can't write numfile: $!";
987 close $fh or die "can't close numfile: $!";
989 Here's a much better web-page hit counter:
991 $hits = int( (time() - 850_000_000) / rand(1_000) );
993 If the count doesn't impress your friends, then the code might. :-)
995 =head2 All I want to do is append a small amount of text to the end of a file. Do I still have to use locking?
996 X<append> X<file, append>
998 If you are on a system that correctly implements C<flock> and you use
999 the example appending code from "perldoc -f flock" everything will be
1000 OK even if the OS you are on doesn't implement append mode correctly
1001 (if such a system exists.) So if you are happy to restrict yourself to
1002 OSs that implement C<flock> (and that's not really much of a
1003 restriction) then that is what you should do.
1005 If you know you are only going to use a system that does correctly
1006 implement appending (i.e. not Win32) then you can omit the C<seek>
1007 from the code in the previous answer.
1009 If you know you are only writing code to run on an OS and filesystem
1010 that does implement append mode correctly (a local filesystem on a
1011 modern Unix for example), and you keep the file in block-buffered mode
1012 and you write less than one buffer-full of output between each manual
1013 flushing of the buffer then each bufferload is almost guaranteed to be
1014 written to the end of the file in one chunk without getting
1015 intermingled with anyone else's output. You can also use the
1016 C<syswrite> function which is simply a wrapper around your system's
1017 C<write(2)> system call.
1019 There is still a small theoretical chance that a signal will interrupt
1020 the system level C<write()> operation before completion. There is also
1021 a possibility that some STDIO implementations may call multiple system
1022 level C<write()>s even if the buffer was empty to start. There may be
1023 some systems where this probability is reduced to zero, and this is
1024 not a concern when using C<:perlio> instead of your system's STDIO.
1026 =head2 How do I randomly update a binary file?
1027 X<file, binary patch>
1029 If you're just trying to patch a binary, in many cases something as
1030 simple as this works:
1032 perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs
1034 However, if you have fixed sized records, then you might do something more
1037 $RECSIZE = 220; # size of record, in bytes
1038 $recno = 37; # which record to update
1039 open my $fh, '+<', 'somewhere' or die "can't update somewhere: $!";
1040 seek $fh, $recno * $RECSIZE, 0;
1041 read $fh, $record, $RECSIZE == $RECSIZE or die "can't read record $recno: $!";
1043 seek $fh, -$RECSIZE, 1;
1047 Locking and error checking are left as an exercise for the reader.
1048 Don't forget them or you'll be quite sorry.
1050 =head2 How do I get a file's timestamp in perl?
1051 X<timestamp> X<file, timestamp>
1053 If you want to retrieve the time at which the file was last read,
1054 written, or had its meta-data (owner, etc) changed, you use the B<-A>,
1055 B<-M>, or B<-C> file test operations as documented in L<perlfunc>.
1056 These retrieve the age of the file (measured against the start-time of
1057 your program) in days as a floating point number. Some platforms may
1058 not have all of these times. See L<perlport> for details. To retrieve
1059 the "raw" time in seconds since the epoch, you would call the stat
1060 function, then use C<localtime()>, C<gmtime()>, or
1061 C<POSIX::strftime()> to convert this into human-readable form.
1065 my $write_secs = (stat($file))[9];
1066 printf "file %s updated at %s\n", $file,
1067 scalar localtime($write_secs);
1069 If you prefer something more legible, use the File::stat module
1070 (part of the standard distribution in version 5.004 and later):
1072 # error checking left as an exercise for reader.
1074 use Time::localtime;
1075 my $date_string = ctime(stat($file)->mtime);
1076 print "file $file updated at $date_string\n";
1078 The POSIX::strftime() approach has the benefit of being,
1079 in theory, independent of the current locale. See L<perllocale>
1082 =head2 How do I set a file's timestamp in perl?
1083 X<timestamp> X<file, timestamp>
1085 You use the utime() function documented in L<perlfunc/utime>.
1086 By way of example, here's a little program that copies the
1087 read and write times from its first argument to all the rest
1091 die "usage: cptimes timestamp_file other_files ...\n";
1093 my $timestamp = shift;
1094 my($atime, $mtime) = (stat($timestamp))[8,9];
1095 utime $atime, $mtime, @ARGV;
1097 Error checking is, as usual, left as an exercise for the reader.
1099 The perldoc for utime also has an example that has the same
1100 effect as touch(1) on files that I<already exist>.
1102 Certain file systems have a limited ability to store the times
1103 on a file at the expected level of precision. For example, the
1104 FAT and HPFS filesystem are unable to create dates on files with
1105 a finer granularity than two seconds. This is a limitation of
1106 the filesystems, not of utime().
1108 =head2 How do I print to more than one file at once?
1109 X<print, to multiple files>
1111 To connect one filehandle to several output filehandles,
1112 you can use the IO::Tee or Tie::FileHandle::Multiplex modules.
1114 If you only have to do this once, you can print individually
1117 for my $fh (FH1, FH2, FH3) { print $fh "whatever\n" }
1119 =head2 How can I read in an entire file all at once?
1120 X<slurp> X<file, slurping>
1122 Are you sure you want to read the entire file and store it in memory?
1123 If you mmap the file, you can virtually load the entire file into a
1124 string without actually storing it in memory:
1126 use File::Map qw(map_file);
1128 map_file my $string, $filename;
1130 Once mapped, you can treat C<$string> as you would any other string.
1131 Since you don't necessarily have to load the data, mmap-ing can be
1132 very fast and may not increase your memory footprint.
1134 If you want to load the entire file, you can use the C<File::Slurp>
1135 module to do it in one one simple and efficient step:
1139 my $all_of_it = read_file($filename); # entire file in scalar
1140 my @all_lines = read_file($filename); # one line per element
1142 The customary Perl approach for processing all the lines in a file is to
1143 do so one line at a time:
1145 open my $input, '<', $file or die "can't open $file: $!";
1148 # do something with $_
1150 close $input or die "can't close $file: $!";
1152 This is tremendously more efficient than reading the entire file into
1153 memory as an array of lines and then processing it one element at a time,
1154 which is often--if not almost always--the wrong approach. Whenever
1155 you see someone do this:
1157 my @lines = <INPUT>;
1159 You should think long and hard about why you need everything loaded at
1160 once. It's just not a scalable solution. You might also find it more
1161 fun to use the standard C<Tie::File> module, or the C<DB_File> module's
1162 C<$DB_RECNO> bindings, which allow you to tie an array to a file so that
1163 accessing an element the array actually accesses the corresponding
1166 You can read the entire filehandle contents into a scalar.
1171 open my $fh, '<', $file or die "can't open $file: $!";
1175 That temporarily undefs your record separator, and will automatically
1176 close the file at block exit. If the file is already open, just use this:
1178 my $var = do { local $/; <$fh> };
1180 You can do that one better by using a localized C<@ARGV> so you can
1181 eliminate the C<open>:
1183 my $var = do { local( @ARGV, $/ ) = $file; <> };
1185 For ordinary files you can also use the C<read> function.
1187 read( $fh, $var, -s $fh );
1189 That third argument tests the byte size of the data on the C<INPUT> filehandle
1190 and reads that many bytes into the buffer C<$var>.
1192 =head2 How can I read in a file by paragraphs?
1193 X<file, reading by paragraphs>
1195 Use the C<$/> variable (see L<perlvar> for details). You can either
1196 set it to C<""> to eliminate empty paragraphs (C<"abc\n\n\n\ndef">,
1197 for instance, gets treated as two paragraphs and not three), or
1198 C<"\n\n"> to accept empty paragraphs.
1200 Note that a blank line must have no blanks in it. Thus
1201 S<C<"fred\n \nstuff\n\n">> is one paragraph, but C<"fred\n\nstuff\n\n"> is two.
1203 =head2 How can I read a single character from a file? From the keyboard?
1204 X<getc> X<file, reading one character at a time>
1206 You can use the builtin C<getc()> function for most filehandles, but
1207 it won't (easily) work on a terminal device. For STDIN, either use
1208 the Term::ReadKey module from CPAN or use the sample code in
1211 If your system supports the portable operating system programming
1212 interface (POSIX), you can use the following code, which you'll note
1213 turns off echo processing as well.
1226 use POSIX qw(:termios_h);
1228 my ($term, $oterm, $echo, $noecho, $fd_stdin);
1230 my $fd_stdin = fileno(STDIN);
1232 $term = POSIX::Termios->new();
1233 $term->getattr($fd_stdin);
1234 $oterm = $term->getlflag();
1236 $echo = ECHO | ECHOK | ICANON;
1237 $noecho = $oterm & ~$echo;
1240 $term->setlflag($noecho);
1241 $term->setcc(VTIME, 1);
1242 $term->setattr($fd_stdin, TCSANOW);
1246 $term->setlflag($oterm);
1247 $term->setcc(VTIME, 0);
1248 $term->setattr($fd_stdin, TCSANOW);
1254 sysread(STDIN, $key, 1);
1263 The Term::ReadKey module from CPAN may be easier to use. Recent versions
1264 include also support for non-portable systems as well.
1267 open my $tty, '<', '/dev/tty';
1268 print "Gimme a char: ";
1270 my $key = ReadKey 0, $tty;
1272 printf "\nYou said %s, char number %03d\n",
1275 =head2 How can I tell whether there's a character waiting on a filehandle?
1277 The very first thing you should do is look into getting the Term::ReadKey
1278 extension from CPAN. As we mentioned earlier, it now even has limited
1279 support for non-portable (read: not open systems, closed, proprietary,
1280 not POSIX, not Unix, etc.) systems.
1282 You should also check out the Frequently Asked Questions list in
1283 comp.unix.* for things like this: the answer is essentially the same.
1284 It's very system dependent. Here's one solution that works on BSD
1289 vec($rin, fileno(STDIN), 1) = 1;
1290 return $nfd = select($rin,undef,undef,0);
1293 If you want to find out how many characters are waiting, there's
1294 also the FIONREAD ioctl call to be looked at. The I<h2ph> tool that
1295 comes with Perl tries to convert C include files to Perl code, which
1296 can be C<require>d. FIONREAD ends up defined as a function in the
1297 I<sys/ioctl.ph> file:
1299 require 'sys/ioctl.ph';
1301 $size = pack("L", 0);
1302 ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n";
1303 $size = unpack("L", $size);
1305 If I<h2ph> wasn't installed or doesn't work for you, you can
1306 I<grep> the include files by hand:
1308 % grep FIONREAD /usr/include/*/*
1309 /usr/include/asm/ioctls.h:#define FIONREAD 0x541B
1311 Or write a small C program using the editor of champions:
1314 #include <sys/ioctl.h>
1316 printf("%#08x\n", FIONREAD);
1319 % cc -o fionread fionread.c
1323 And then hard code it, leaving porting as an exercise to your successor.
1325 $FIONREAD = 0x4004667f; # XXX: opsys dependent
1327 $size = pack("L", 0);
1328 ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n";
1329 $size = unpack("L", $size);
1331 FIONREAD requires a filehandle connected to a stream, meaning that sockets,
1332 pipes, and tty devices work, but I<not> files.
1334 =head2 How do I do a C<tail -f> in perl?
1335 X<tail> X<IO::Handle> X<File::Tail> X<clearerr>
1341 The statement C<seek(GWFILE, 0, 1)> doesn't change the current position,
1342 but it does clear the end-of-file condition on the handle, so that the
1343 next C<< <GWFILE> >> makes Perl try again to read something.
1345 If that doesn't work (it relies on features of your stdio implementation),
1346 then you need something more like this:
1349 for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE)) {
1350 # search for some stuff and put it into files
1353 seek(GWFILE, $curpos, 0); # seek to where we had been
1356 If this still doesn't work, look into the C<clearerr> method
1357 from C<IO::Handle>, which resets the error and end-of-file states
1360 There's also a C<File::Tail> module from CPAN.
1362 =head2 How do I dup() a filehandle in Perl?
1365 If you check L<perlfunc/open>, you'll see that several of the ways
1366 to call open() should do the trick. For example:
1368 open my $log, '>>', '/foo/logfile';
1369 open STDERR, '>&LOG';
1371 Or even with a literal numeric descriptor:
1373 my $fd = $ENV{MHCONTEXTFD};
1374 open $mhcontext, "<&=$fd"; # like fdopen(3S)
1376 Note that "<&STDIN" makes a copy, but "<&=STDIN" make
1377 an alias. That means if you close an aliased handle, all
1378 aliases become inaccessible. This is not true with
1381 Error checking, as always, has been left as an exercise for the reader.
1383 =head2 How do I close a file descriptor by number?
1384 X<file, closing file descriptors> X<POSIX> X<close>
1386 If, for some reason, you have a file descriptor instead of a
1387 filehandle (perhaps you used C<POSIX::open>), you can use the
1388 C<close()> function from the C<POSIX> module:
1392 POSIX::close( $fd );
1394 This should rarely be necessary, as the Perl C<close()> function is to be
1395 used for things that Perl opened itself, even if it was a dup of a
1396 numeric descriptor as with C<MHCONTEXT> above. But if you really have
1397 to, you may be able to do this:
1399 require 'sys/syscall.ph';
1400 my $rc = syscall(&SYS_close, $fd + 0); # must force numeric
1401 die "can't sysclose $fd: $!" unless $rc == -1;
1403 Or, just use the fdopen(3S) feature of C<open()>:
1406 open my( $fh ), "<&=$fd" or die "Cannot reopen fd=$fd: $!";
1410 =head2 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?
1411 X<filename, DOS issues>
1413 Whoops! You just put a tab and a formfeed into that filename!
1414 Remember that within double quoted strings ("like\this"), the
1415 backslash is an escape character. The full list of these is in
1416 L<perlop/Quote and Quote-like Operators>. Unsurprisingly, you don't
1417 have a file called "c:(tab)emp(formfeed)oo" or
1418 "c:(tab)emp(formfeed)oo.exe" on your legacy DOS filesystem.
1420 Either single-quote your strings, or (preferably) use forward slashes.
1421 Since all DOS and Windows versions since something like MS-DOS 2.0 or so
1422 have treated C</> and C<\> the same in a path, you might as well use the
1423 one that doesn't clash with Perl--or the POSIX shell, ANSI C and C++,
1424 awk, Tcl, Java, or Python, just to mention a few. POSIX paths
1425 are more portable, too.
1427 =head2 Why doesn't glob("*.*") get all the files?
1430 Because even on non-Unix ports, Perl's glob function follows standard
1431 Unix globbing semantics. You'll need C<glob("*")> to get all (non-hidden)
1432 files. This makes glob() portable even to legacy systems. Your
1433 port may include proprietary globbing functions as well. Check its
1434 documentation for details.
1436 =head2 Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl?
1438 This is elaborately and painstakingly described in the
1439 F<file-dir-perms> article in the "Far More Than You Ever Wanted To
1440 Know" collection in http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz .
1442 The executive summary: learn how your filesystem works. The
1443 permissions on a file say what can happen to the data in that file.
1444 The permissions on a directory say what can happen to the list of
1445 files in that directory. If you delete a file, you're removing its
1446 name from the directory (so the operation depends on the permissions
1447 of the directory, not of the file). If you try to write to the file,
1448 the permissions of the file govern whether you're allowed to.
1450 =head2 How do I select a random line from a file?
1451 X<file, selecting a random line>
1453 Short of loading the file into a database or pre-indexing the lines in
1454 the file, there are a couple of things that you can do.
1456 Here's a reservoir-sampling algorithm from the Camel Book:
1459 rand($.) < 1 && ($line = $_) while <>;
1461 This has a significant advantage in space over reading the whole file
1462 in. You can find a proof of this method in I<The Art of Computer
1463 Programming>, Volume 2, Section 3.4.2, by Donald E. Knuth.
1465 You can use the C<File::Random> module which provides a function
1468 use File::Random qw/random_line/;
1469 my $line = random_line($filename);
1471 Another way is to use the C<Tie::File> module, which treats the entire
1472 file as an array. Simply access a random array element.
1474 =head2 Why do I get weird spaces when I print an array of lines?
1476 (contributed by brian d foy)
1478 If you are seeing spaces between the elements of your array when
1479 you print the array, you are probably interpolating the array in
1482 my @animals = qw(camel llama alpaca vicuna);
1483 print "animals are: @animals\n";
1485 It's the double quotes, not the C<print>, doing this. Whenever you
1486 interpolate an array in a double quote context, Perl joins the
1487 elements with spaces (or whatever is in C<$">, which is a space by
1490 animals are: camel llama alpaca vicuna
1492 This is different than printing the array without the interpolation:
1494 my @animals = qw(camel llama alpaca vicuna);
1495 print "animals are: ", @animals, "\n";
1497 Now the output doesn't have the spaces between the elements because
1498 the elements of C<@animals> simply become part of the list to
1501 animals are: camelllamaalpacavicuna
1503 You might notice this when each of the elements of C<@array> end with
1504 a newline. You expect to print one element per line, but notice that
1505 every line after the first is indented:
1508 this is another line
1509 this is the third line
1511 That extra space comes from the interpolation of the array. If you
1512 don't want to put anything between your array elements, don't use the
1513 array in double quotes. You can send it to print without them:
1517 =head2 How do I traverse a directory tree?
1519 (contributed by brian d foy)
1521 The C<File::Find> module, which comes with Perl, does all of the hard
1522 work to traverse a directory structure. It comes with Perl. You simply
1523 call the C<find> subroutine with a callback subroutine and the
1524 directories you want to traverse:
1528 find( \&wanted, @directories );
1531 # full path in $File::Find::name
1532 # just filename in $_
1533 ... do whatever you want to do ...
1536 The C<File::Find::Closures>, which you can download from CPAN, provides
1537 many ready-to-use subroutines that you can use with C<File::Find>.
1539 The C<File::Finder>, which you can download from CPAN, can help you
1540 create the callback subroutine using something closer to the syntax of
1541 the C<find> command-line utility:
1546 my $deep_dirs = File::Finder->depth->type('d')->ls->exec('rmdir','{}');
1548 find( $deep_dirs->as_options, @places );
1550 The C<File::Find::Rule> module, which you can download from CPAN, has
1551 a similar interface, but does the traversal for you too:
1553 use File::Find::Rule;
1555 my @files = File::Find::Rule->file()
1559 =head2 How do I delete a directory tree?
1561 (contributed by brian d foy)
1563 If you have an empty directory, you can use Perl's built-in C<rmdir>.
1564 If the directory is not empty (so, no files or subdirectories), you
1565 either have to empty it yourself (a lot of work) or use a module to
1568 The C<File::Path> module, which comes with Perl, has a C<remove_tree>
1569 which can take care of all of the hard work for you:
1571 use File::Path qw(remove_tree);
1573 remove_tree( @directories );
1575 The C<File::Path> module also has a legacy interface to the older
1576 C<rmtree> subroutine.
1578 =head2 How do I copy an entire directory?
1580 (contributed by Shlomi Fish)
1582 To do the equivalent of C<cp -R> (i.e. copy an entire directory tree
1583 recursively) in portable Perl, you'll either need to write something yourself
1584 or find a good CPAN module such as L<File::Copy::Recursive>.
1586 =head1 AUTHOR AND COPYRIGHT
1588 Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and
1589 other authors as noted. All rights reserved.
1591 This documentation is free; you can redistribute it and/or modify it
1592 under the same terms as Perl itself.
1594 Irrespective of its distribution, all code examples here are in the public
1595 domain. You are permitted and encouraged to use this code and any
1596 derivatives thereof in your own programs for fun or for profit as you
1597 see fit. A simple comment in the code giving credit to the FAQ would
1598 be courteous but is not required.