Commit | Line | Data |
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68dc0745 | 1 | =head1 NAME |
2 | ||
109f0441 | 3 | perlfaq5 - Files and Formats |
68dc0745 | 4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | This section deals with I/O and the "f" issues: filehandles, flushing, | |
8 | formats, and footers. | |
9 | ||
5a964f20 | 10 | =head2 How do I flush/unbuffer an output filehandle? Why must I do this? |
d74e8afc | 11 | X<flush> X<buffer> X<unbuffer> X<autoflush> |
68dc0745 | 12 | |
109f0441 | 13 | (contributed by brian d foy) |
5a964f20 | 14 | |
109f0441 S |
15 | You might like to read Mark Jason Dominus's "Suffering From Buffering" |
16 | at http://perl.plover.com/FAQs/Buffering.html . | |
68dc0745 | 17 | |
109f0441 S |
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: | |
24 | ||
25 | # long wait, then row of dots all at once | |
26 | while( <> ) { | |
27 | print "."; | |
28 | print "\n" unless ++$count % 50; | |
29 | ||
30 | #... expensive line processing operations | |
31 | } | |
32 | ||
33 | To get around this, you have to unbuffer the output filehandle, in this | |
34 | case, C<STDOUT>. You can set the special variable C<$|> to a true value | |
35 | (mnemonic: making your filehandles "piping hot"): | |
36 | ||
37 | $|++; | |
38 | ||
39 | # dot shown immediately | |
40 | while( <> ) { | |
41 | print "."; | |
42 | print "\n" unless ++$count % 50; | |
43 | ||
44 | #... expensive line processing operations | |
45 | } | |
46 | ||
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): | |
51 | ||
52 | { | |
53 | my $previous_default = select(STDOUT); # save previous default | |
54 | $|++; # autoflush STDOUT | |
55 | select(STDERR); | |
56 | $|++; # autoflush STDERR, to be sure | |
57 | select($previous_default); # restore previous default | |
58 | } | |
68dc0745 | 59 | |
109f0441 S |
60 | # now should alternate . and + |
61 | while( 1 ) | |
62 | { | |
63 | sleep 1; | |
64 | print STDOUT "."; | |
65 | print STDERR "+"; | |
66 | print STDOUT "\n" unless ++$count % 25; | |
67 | } | |
68 | ||
69 | Besides the C<$|> special variable, you can use C<binmode> to give | |
70 | your filehandle a C<:unix> layer, which is unbuffered: | |
71 | ||
72 | binmode( STDOUT, ":unix" ); | |
68dc0745 | 73 | |
109f0441 S |
74 | while( 1 ) { |
75 | sleep 1; | |
76 | print "."; | |
77 | print "\n" unless ++$count % 50; | |
78 | } | |
68dc0745 | 79 | |
109f0441 S |
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. | |
68dc0745 | 82 | |
109f0441 S |
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 | |
85 | filehandle: | |
c195e131 RGS |
86 | |
87 | use IO::Handle; | |
109f0441 S |
88 | open my( $io_fh ), ">", "output.txt"; |
89 | $io_fh->autoflush(1); | |
90 | ||
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 | |
c195e131 | 93 | |
109f0441 | 94 | $io_fh->flush; |
487af187 | 95 | |
e573f903 | 96 | =head2 How do I change, delete, or insert a line in a file, or append to the beginning of a file? |
d74e8afc | 97 | X<file, editing> |
68dc0745 | 98 | |
e573f903 RGS |
99 | (contributed by brian d foy) |
100 | ||
101 | The basic idea of inserting, changing, or deleting a line from a text | |
102 | file involves reading and printing the file to the point you want to | |
103 | make the change, making the change, then reading and printing the rest | |
104 | of the file. Perl doesn't provide random access to lines (especially | |
105 | since the record input separator, C<$/>, is mutable), although modules | |
106 | such as C<Tie::File> can fake it. | |
107 | ||
108 | A Perl program to do these tasks takes the basic form of opening a | |
109 | file, printing its lines, then closing the file: | |
110 | ||
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: $!"; | |
113 | ||
114 | while( <$in> ) | |
115 | { | |
116 | print $out $_; | |
117 | } | |
118 | ||
119 | close $out; | |
120 | ||
121 | Within that basic form, add the parts that you need to insert, change, | |
122 | or delete lines. | |
123 | ||
124 | To prepend lines to the beginning, print those lines before you enter | |
125 | the loop that prints the existing lines. | |
126 | ||
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: $!"; | |
129 | ||
109f0441 | 130 | print $out "# Add this line to the top\n"; # <--- HERE'S THE MAGIC |
e573f903 RGS |
131 | |
132 | while( <$in> ) | |
133 | { | |
134 | print $out $_; | |
135 | } | |
136 | ||
137 | close $out; | |
138 | ||
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! | |
143 | ||
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: $!"; | |
146 | ||
109f0441 | 147 | print $out "# Add this line to the top\n"; |
e573f903 RGS |
148 | |
149 | while( <$in> ) | |
150 | { | |
151 | s/\b(perl)\b/Perl/g; | |
152 | print $out $_; | |
153 | } | |
154 | ||
155 | close $out; | |
156 | ||
157 | To change only a particular line, the input line number, C<$.>, is | |
ee891a00 RGS |
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: | |
e573f903 | 161 | |
ee891a00 | 162 | while( <$in> ) # print the lines before the change |
e573f903 | 163 | { |
e573f903 | 164 | print $out $_; |
ee891a00 | 165 | last if $. == 4; # line number before change |
e573f903 RGS |
166 | } |
167 | ||
ee891a00 RGS |
168 | my $line = <$in>; |
169 | $line =~ s/\b(perl)\b/Perl/g; | |
170 | print $out $line; | |
171 | ||
172 | while( <$in> ) # print the rest of the lines | |
173 | { | |
174 | print $out $_; | |
175 | } | |
109f0441 | 176 | |
e573f903 RGS |
177 | To skip lines, use the looping controls. The C<next> in this example |
178 | skips comment lines, and the C<last> stops all processing once it | |
179 | encounters either C<__END__> or C<__DATA__>. | |
180 | ||
181 | while( <$in> ) | |
182 | { | |
183 | next if /^\s+#/; # skip comment lines | |
184 | last if /^__(END|DATA)__$/; # stop at end of code marker | |
185 | print $out $_; | |
186 | } | |
187 | ||
188 | Do the same sort of thing to delete a particular line by using C<next> | |
189 | to skip the lines you don't want to show up in the output. This | |
190 | example skips every fifth line: | |
191 | ||
192 | while( <$in> ) | |
193 | { | |
194 | next unless $. % 5; | |
195 | print $out $_; | |
196 | } | |
197 | ||
198 | If, for some odd reason, you really want to see the whole file at once | |
f12f5f55 | 199 | rather than processing line-by-line, you can slurp it in (as long as |
e573f903 RGS |
200 | you can fit the whole thing in memory!): |
201 | ||
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: $!"; | |
204 | ||
205 | my @lines = do { local $/; <$in> }; # slurp! | |
206 | ||
207 | # do your magic here | |
208 | ||
209 | print $out @lines; | |
210 | ||
211 | Modules such as C<File::Slurp> and C<Tie::File> can help with that | |
212 | too. If you can, however, avoid reading the entire file at once. Perl | |
213 | won't give that memory back to the operating system until the process | |
214 | finishes. | |
215 | ||
216 | You can also use Perl one-liners to modify a file in-place. The | |
217 | following changes all 'Fred' to 'Barney' in F<inFile.txt>, overwriting | |
218 | the file with the new contents. With the C<-p> switch, Perl wraps a | |
219 | C<while> loop around the code you specify with C<-e>, and C<-i> turns | |
220 | on in-place editing. The current line is in C<$_>. With C<-p>, Perl | |
221 | automatically prints the value of C<$_> at the end of the loop. See | |
222 | L<perlrun> for more details. | |
223 | ||
224 | perl -pi -e 's/Fred/Barney/' inFile.txt | |
225 | ||
226 | To make a backup of C<inFile.txt>, give C<-i> a file extension to add: | |
227 | ||
228 | perl -pi.bak -e 's/Fred/Barney/' inFile.txt | |
229 | ||
230 | To change only the fifth line, you can add a test checking C<$.>, the | |
231 | input line number, then only perform the operation when the test | |
232 | passes: | |
233 | ||
234 | perl -pi -e 's/Fred/Barney/ if $. == 5' inFile.txt | |
235 | ||
236 | To add lines before a certain line, you can add a line (or lines!) | |
237 | before Perl prints C<$_>: | |
238 | ||
239 | perl -pi -e 'print "Put before third line\n" if $. == 3' inFile.txt | |
240 | ||
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: | |
243 | ||
244 | perl -pi -e 'print "Put before first line\n" if $. == 1' inFile.txt | |
245 | ||
246 | To insert a line after one already in the file, use the C<-n> switch. | |
247 | It's just like C<-p> except that it doesn't print C<$_> 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. | |
250 | ||
251 | perl -ni -e 'print; print "Put after fifth line\n" if $. == 5' inFile.txt | |
252 | ||
253 | To delete lines, only print the ones that you want. | |
254 | ||
255 | perl -ni -e 'print unless /d/' inFile.txt | |
256 | ||
257 | ... or ... | |
258 | ||
259 | perl -pi -e 'next unless /d/' inFile.txt | |
68dc0745 | 260 | |
261 | =head2 How do I count the number of lines in a file? | |
d74e8afc | 262 | X<file, counting lines> X<lines> X<line> |
68dc0745 | 263 | |
264 | One fairly efficient way is to count newlines in the file. The | |
265 | following program uses a feature of tr///, as documented in L<perlop>. | |
266 | If your text file doesn't end with a newline, then it's not really a | |
267 | proper text file, so this may report one fewer line than you expect. | |
268 | ||
500071f4 RGS |
269 | $lines = 0; |
270 | open(FILE, $filename) or die "Can't open `$filename': $!"; | |
271 | while (sysread FILE, $buffer, 4096) { | |
272 | $lines += ($buffer =~ tr/\n//); | |
273 | } | |
274 | close FILE; | |
68dc0745 | 275 | |
5a964f20 TC |
276 | This assumes no funny games with newline translations. |
277 | ||
4750257b | 278 | =head2 How can I use Perl's C<-i> option from within a program? |
d74e8afc | 279 | X<-i> X<in-place> |
4750257b MJD |
280 | |
281 | C<-i> sets the value of Perl's C<$^I> variable, which in turn affects | |
282 | the behavior of C<< <> >>; see L<perlrun> for more details. By | |
283 | modifying the appropriate variables directly, you can get the same | |
284 | behavior within a larger program. For example: | |
285 | ||
500071f4 RGS |
286 | # ... |
287 | { | |
288 | local($^I, @ARGV) = ('.orig', glob("*.c")); | |
289 | while (<>) { | |
290 | if ($. == 1) { | |
291 | print "This line should appear at the top of each file\n"; | |
292 | } | |
293 | s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case | |
294 | print; | |
295 | close ARGV if eof; # Reset $. | |
296 | } | |
297 | } | |
298 | # $^I and @ARGV return to their old values here | |
4750257b MJD |
299 | |
300 | This block modifies all the C<.c> files in the current directory, | |
301 | leaving a backup of the original data from each file in a new | |
302 | C<.c.orig> file. | |
303 | ||
7678cced | 304 | =head2 How can I copy a file? |
109f0441 | 305 | X<copy> X<file, copy> X<File::Copy> |
7678cced RGS |
306 | |
307 | (contributed by brian d foy) | |
308 | ||
109f0441 | 309 | Use the C<File::Copy> module. It comes with Perl and can do a |
7678cced RGS |
310 | true copy across file systems, and it does its magic in |
311 | a portable fashion. | |
312 | ||
313 | use File::Copy; | |
314 | ||
315 | copy( $original, $new_copy ) or die "Copy failed: $!"; | |
316 | ||
109f0441 | 317 | If you can't use C<File::Copy>, you'll have to do the work yourself: |
7678cced | 318 | open the original file, open the destination file, then print |
109f0441 S |
319 | to the destination file as you read the original. You also have to |
320 | remember to copy the permissions, owner, and group to the new file. | |
7678cced | 321 | |
68dc0745 | 322 | =head2 How do I make a temporary file name? |
d74e8afc | 323 | X<file, temporary> |
68dc0745 | 324 | |
7678cced | 325 | If you don't need to know the name of the file, you can use C<open()> |
109f0441 S |
326 | with C<undef> in place of the file name. In Perl 5.8 or later, the |
327 | C<open()> function creates an anonymous temporary file: | |
7678cced RGS |
328 | |
329 | open my $tmp, '+>', undef or die $!; | |
6670e5e7 | 330 | |
7678cced | 331 | Otherwise, you can use the File::Temp module. |
68dc0745 | 332 | |
500071f4 | 333 | use File::Temp qw/ tempfile tempdir /; |
a6dd486b | 334 | |
500071f4 RGS |
335 | $dir = tempdir( CLEANUP => 1 ); |
336 | ($fh, $filename) = tempfile( DIR => $dir ); | |
5a964f20 | 337 | |
500071f4 | 338 | # or if you don't need to know the filename |
5a964f20 | 339 | |
500071f4 | 340 | $fh = tempfile( DIR => $dir ); |
5a964f20 | 341 | |
16394a69 JH |
342 | The File::Temp has been a standard module since Perl 5.6.1. If you |
343 | don't have a modern enough Perl installed, use the C<new_tmpfile> | |
344 | class method from the IO::File module to get a filehandle opened for | |
345 | reading and writing. Use it if you don't need to know the file's name: | |
5a964f20 | 346 | |
500071f4 RGS |
347 | use IO::File; |
348 | $fh = IO::File->new_tmpfile() | |
16394a69 | 349 | or die "Unable to make new temporary file: $!"; |
5a964f20 | 350 | |
a6dd486b JB |
351 | If you're committed to creating a temporary file by hand, use the |
352 | process ID and/or the current time-value. If you need to have many | |
353 | temporary files in one process, use a counter: | |
5a964f20 | 354 | |
500071f4 | 355 | BEGIN { |
68dc0745 | 356 | use Fcntl; |
16394a69 | 357 | my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMPDIR} || $ENV{TEMP}; |
c195e131 | 358 | my $base_name = sprintf "%s/%d-%d-0000", $temp_dir, $$, time; |
500071f4 | 359 | |
68dc0745 | 360 | sub temp_file { |
500071f4 RGS |
361 | local *FH; |
362 | my $count = 0; | |
c195e131 RGS |
363 | until( defined(fileno(FH)) || $count++ > 100 ) { |
364 | $base_name =~ s/-(\d+)$/"-" . (1 + $1)/e; | |
365 | # O_EXCL is required for security reasons. | |
366 | sysopen FH, $base_name, O_WRONLY|O_EXCL|O_CREAT; | |
367 | } | |
368 | ||
369 | if( defined fileno(FH) ) { | |
370 | return (*FH, $base_name); | |
371 | } | |
372 | else { | |
373 | return (); | |
374 | } | |
500071f4 | 375 | } |
109f0441 | 376 | |
500071f4 | 377 | } |
68dc0745 | 378 | |
68dc0745 | 379 | =head2 How can I manipulate fixed-record-length files? |
d74e8afc | 380 | X<fixed-length> X<file, fixed-length records> |
68dc0745 | 381 | |
793f5136 RGS |
382 | The most efficient way is using L<pack()|perlfunc/"pack"> and |
383 | L<unpack()|perlfunc/"unpack">. This is faster than using | |
384 | L<substr()|perlfunc/"substr"> when taking many, many strings. It is | |
385 | slower for just a few. | |
5a964f20 TC |
386 | |
387 | Here is a sample chunk of code to break up and put back together again | |
388 | some fixed-format input lines, in this case from the output of a normal, | |
389 | Berkeley-style ps: | |
68dc0745 | 390 | |
500071f4 RGS |
391 | # sample input line: |
392 | # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what | |
393 | my $PS_T = 'A6 A4 A7 A5 A*'; | |
394 | open my $ps, '-|', 'ps'; | |
395 | print scalar <$ps>; | |
396 | my @fields = qw( pid tt stat time command ); | |
397 | while (<$ps>) { | |
398 | my %process; | |
399 | @process{@fields} = unpack($PS_T, $_); | |
793f5136 | 400 | for my $field ( @fields ) { |
500071f4 | 401 | print "$field: <$process{$field}>\n"; |
68dc0745 | 402 | } |
793f5136 | 403 | print 'line=', pack($PS_T, @process{@fields} ), "\n"; |
500071f4 | 404 | } |
68dc0745 | 405 | |
793f5136 RGS |
406 | We've used a hash slice in order to easily handle the fields of each row. |
407 | Storing the keys in an array means it's easy to operate on them as a | |
408 | group or loop over them with for. It also avoids polluting the program | |
409 | with global variables and using symbolic references. | |
5a964f20 | 410 | |
ac9dac7f | 411 | =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? |
d74e8afc | 412 | X<filehandle, local> X<filehandle, passing> X<filehandle, reference> |
68dc0745 | 413 | |
c90536be JH |
414 | As of perl5.6, open() autovivifies file and directory handles |
415 | as references if you pass it an uninitialized scalar variable. | |
416 | You can then pass these references just like any other scalar, | |
417 | and use them in the place of named handles. | |
68dc0745 | 418 | |
c90536be | 419 | open my $fh, $file_name; |
818c4caa | 420 | |
c90536be | 421 | open local $fh, $file_name; |
818c4caa | 422 | |
c90536be | 423 | print $fh "Hello World!\n"; |
818c4caa | 424 | |
c90536be | 425 | process_file( $fh ); |
68dc0745 | 426 | |
500071f4 RGS |
427 | If you like, you can store these filehandles in an array or a hash. |
428 | If you access them directly, they aren't simple scalars and you | |
ac9dac7f | 429 | need to give C<print> a little help by placing the filehandle |
500071f4 RGS |
430 | reference in braces. Perl can only figure it out on its own when |
431 | the filehandle reference is a simple scalar. | |
432 | ||
433 | my @fhs = ( $fh1, $fh2, $fh3 ); | |
ac9dac7f | 434 | |
500071f4 RGS |
435 | for( $i = 0; $i <= $#fhs; $i++ ) { |
436 | print {$fhs[$i]} "just another Perl answer, \n"; | |
437 | } | |
438 | ||
c90536be JH |
439 | Before perl5.6, you had to deal with various typeglob idioms |
440 | which you may see in older code. | |
68dc0745 | 441 | |
c90536be JH |
442 | open FILE, "> $filename"; |
443 | process_typeglob( *FILE ); | |
444 | process_reference( \*FILE ); | |
818c4caa | 445 | |
c90536be JH |
446 | sub process_typeglob { local *FH = shift; print FH "Typeglob!" } |
447 | sub process_reference { local $fh = shift; print $fh "Reference!" } | |
5a964f20 | 448 | |
c90536be JH |
449 | If you want to create many anonymous handles, you should |
450 | check out the Symbol or IO::Handle modules. | |
5a964f20 TC |
451 | |
452 | =head2 How can I use a filehandle indirectly? | |
d74e8afc | 453 | X<filehandle, indirect> |
5a964f20 TC |
454 | |
455 | An indirect filehandle is using something other than a symbol | |
456 | in a place that a filehandle is expected. Here are ways | |
a6dd486b | 457 | to get indirect filehandles: |
5a964f20 | 458 | |
500071f4 RGS |
459 | $fh = SOME_FH; # bareword is strict-subs hostile |
460 | $fh = "SOME_FH"; # strict-refs hostile; same package only | |
461 | $fh = *SOME_FH; # typeglob | |
462 | $fh = \*SOME_FH; # ref to typeglob (bless-able) | |
463 | $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob | |
5a964f20 | 464 | |
c90536be | 465 | Or, you can use the C<new> method from one of the IO::* modules to |
5a964f20 TC |
466 | create an anonymous filehandle, store that in a scalar variable, |
467 | and use it as though it were a normal filehandle. | |
468 | ||
500071f4 RGS |
469 | use IO::Handle; # 5.004 or higher |
470 | $fh = IO::Handle->new(); | |
5a964f20 TC |
471 | |
472 | Then use any of those as you would a normal filehandle. Anywhere that | |
473 | Perl is expecting a filehandle, an indirect filehandle may be used | |
474 | instead. An indirect filehandle is just a scalar variable that contains | |
368c9434 | 475 | a filehandle. Functions like C<print>, C<open>, C<seek>, or |
c90536be | 476 | the C<< <FH> >> diamond operator will accept either a named filehandle |
5a964f20 TC |
477 | or a scalar variable containing one: |
478 | ||
500071f4 RGS |
479 | ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR); |
480 | print $ofh "Type it: "; | |
481 | $got = <$ifh> | |
482 | print $efh "What was that: $got"; | |
5a964f20 | 483 | |
368c9434 | 484 | If you're passing a filehandle to a function, you can write |
5a964f20 TC |
485 | the function in two ways: |
486 | ||
500071f4 RGS |
487 | sub accept_fh { |
488 | my $fh = shift; | |
489 | print $fh "Sending to indirect filehandle\n"; | |
490 | } | |
46fc3d4c | 491 | |
5a964f20 | 492 | Or it can localize a typeglob and use the filehandle directly: |
46fc3d4c | 493 | |
500071f4 RGS |
494 | sub accept_fh { |
495 | local *FH = shift; | |
496 | print FH "Sending to localized filehandle\n"; | |
497 | } | |
46fc3d4c | 498 | |
5a964f20 TC |
499 | Both styles work with either objects or typeglobs of real filehandles. |
500 | (They might also work with strings under some circumstances, but this | |
501 | is risky.) | |
502 | ||
500071f4 RGS |
503 | accept_fh(*STDOUT); |
504 | accept_fh($handle); | |
5a964f20 TC |
505 | |
506 | In the examples above, we assigned the filehandle to a scalar variable | |
a6dd486b JB |
507 | before using it. That is because only simple scalar variables, not |
508 | expressions or subscripts of hashes or arrays, can be used with | |
509 | built-ins like C<print>, C<printf>, or the diamond operator. Using | |
8305e449 | 510 | something other than a simple scalar variable as a filehandle is |
5a964f20 TC |
511 | illegal and won't even compile: |
512 | ||
500071f4 RGS |
513 | @fd = (*STDIN, *STDOUT, *STDERR); |
514 | print $fd[1] "Type it: "; # WRONG | |
515 | $got = <$fd[0]> # WRONG | |
516 | print $fd[2] "What was that: $got"; # WRONG | |
5a964f20 TC |
517 | |
518 | With C<print> and C<printf>, you get around this by using a block and | |
519 | an expression where you would place the filehandle: | |
520 | ||
500071f4 RGS |
521 | print { $fd[1] } "funny stuff\n"; |
522 | printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559; | |
523 | # Pity the poor deadbeef. | |
5a964f20 TC |
524 | |
525 | That block is a proper block like any other, so you can put more | |
526 | complicated code there. This sends the message out to one of two places: | |
527 | ||
500071f4 RGS |
528 | $ok = -x "/bin/cat"; |
529 | print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n"; | |
530 | print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n"; | |
5a964f20 TC |
531 | |
532 | This approach of treating C<print> and C<printf> like object methods | |
533 | calls doesn't work for the diamond operator. That's because it's a | |
534 | real operator, not just a function with a comma-less argument. Assuming | |
535 | you've been storing typeglobs in your structure as we did above, you | |
c90536be | 536 | can use the built-in function named C<readline> to read a record just |
c47ff5f1 | 537 | as C<< <> >> does. Given the initialization shown above for @fd, this |
c90536be | 538 | would work, but only because readline() requires a typeglob. It doesn't |
5a964f20 TC |
539 | work with objects or strings, which might be a bug we haven't fixed yet. |
540 | ||
500071f4 | 541 | $got = readline($fd[0]); |
5a964f20 TC |
542 | |
543 | Let it be noted that the flakiness of indirect filehandles is not | |
544 | related to whether they're strings, typeglobs, objects, or anything else. | |
545 | It's the syntax of the fundamental operators. Playing the object | |
546 | game doesn't help you at all here. | |
46fc3d4c | 547 | |
68dc0745 | 548 | =head2 How can I set up a footer format to be used with write()? |
d74e8afc | 549 | X<footer> |
68dc0745 | 550 | |
54310121 | 551 | There's no builtin way to do this, but L<perlform> has a couple of |
68dc0745 | 552 | techniques to make it possible for the intrepid hacker. |
553 | ||
554 | =head2 How can I write() into a string? | |
d74e8afc | 555 | X<write, into a string> |
68dc0745 | 556 | |
c195e131 | 557 | See L<perlform/"Accessing Formatting Internals"> for an C<swrite()> function. |
68dc0745 | 558 | |
c195e131 | 559 | =head2 How can I open a filehandle to a string? |
109f0441 | 560 | X<string> X<open> X<IO::String> X<filehandle> |
c195e131 RGS |
561 | |
562 | (contributed by Peter J. Holzer, hjp-usenet2@hjp.at) | |
563 | ||
109f0441 S |
564 | Since Perl 5.8.0 a file handle referring to a string can be created by |
565 | calling open with a reference to that string instead of the filename. | |
566 | This file handle can then be used to read from or write to the string: | |
c195e131 RGS |
567 | |
568 | open(my $fh, '>', \$string) or die "Could not open string for writing"; | |
569 | print $fh "foo\n"; | |
570 | print $fh "bar\n"; # $string now contains "foo\nbar\n" | |
571 | ||
572 | open(my $fh, '<', \$string) or die "Could not open string for reading"; | |
573 | my $x = <$fh>; # $x now contains "foo\n" | |
574 | ||
575 | With older versions of Perl, the C<IO::String> module provides similar | |
576 | functionality. | |
487af187 | 577 | |
68dc0745 | 578 | =head2 How can I output my numbers with commas added? |
d74e8afc | 579 | X<number, commify> |
68dc0745 | 580 | |
b68463f7 RGS |
581 | (contributed by brian d foy and Benjamin Goldberg) |
582 | ||
583 | You can use L<Number::Format> to separate places in a number. | |
584 | It handles locale information for those of you who want to insert | |
585 | full stops instead (or anything else that they want to use, | |
586 | really). | |
587 | ||
49d635f9 RGS |
588 | This subroutine will add commas to your number: |
589 | ||
590 | sub commify { | |
500071f4 RGS |
591 | local $_ = shift; |
592 | 1 while s/^([-+]?\d+)(\d{3})/$1,$2/; | |
593 | return $_; | |
594 | } | |
49d635f9 RGS |
595 | |
596 | This regex from Benjamin Goldberg will add commas to numbers: | |
68dc0745 | 597 | |
500071f4 | 598 | s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g; |
68dc0745 | 599 | |
49d635f9 | 600 | It is easier to see with comments: |
68dc0745 | 601 | |
500071f4 RGS |
602 | s/( |
603 | ^[-+]? # beginning of number. | |
604 | \d+? # first digits before first comma | |
605 | (?= # followed by, (but not included in the match) : | |
606 | (?>(?:\d{3})+) # some positive multiple of three digits. | |
607 | (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever. | |
608 | ) | |
609 | | # or: | |
610 | \G\d{3} # after the last group, get three digits | |
611 | (?=\d) # but they have to have more digits after them. | |
612 | )/$1,/xg; | |
46fc3d4c | 613 | |
68dc0745 | 614 | =head2 How can I translate tildes (~) in a filename? |
d74e8afc | 615 | X<tilde> X<tilde expansion> |
68dc0745 | 616 | |
109f0441 S |
617 | Use the E<lt>E<gt> (C<glob()>) operator, documented in L<perlfunc>. |
618 | Versions of Perl older than 5.6 require that you have a shell | |
619 | installed that groks tildes. Later versions of Perl have this feature | |
620 | built in. The C<File::KGlob> module (available from CPAN) gives more | |
621 | portable glob functionality. | |
68dc0745 | 622 | |
623 | Within Perl, you may use this directly: | |
624 | ||
625 | $filename =~ s{ | |
626 | ^ ~ # find a leading tilde | |
627 | ( # save this in $1 | |
628 | [^/] # a non-slash character | |
629 | * # repeated 0 or more times (0 means me) | |
630 | ) | |
631 | }{ | |
632 | $1 | |
633 | ? (getpwnam($1))[7] | |
634 | : ( $ENV{HOME} || $ENV{LOGDIR} ) | |
635 | }ex; | |
636 | ||
5a964f20 | 637 | =head2 How come when I open a file read-write it wipes it out? |
d74e8afc | 638 | X<clobber> X<read-write> X<clobbering> X<truncate> X<truncating> |
68dc0745 | 639 | |
640 | Because you're using something like this, which truncates the file and | |
641 | I<then> gives you read-write access: | |
642 | ||
500071f4 | 643 | open(FH, "+> /path/name"); # WRONG (almost always) |
68dc0745 | 644 | |
645 | Whoops. You should instead use this, which will fail if the file | |
197aec24 | 646 | doesn't exist. |
d92eb7b0 | 647 | |
500071f4 | 648 | open(FH, "+< /path/name"); # open for update |
d92eb7b0 | 649 | |
c47ff5f1 | 650 | Using ">" always clobbers or creates. Using "<" never does |
d92eb7b0 | 651 | either. The "+" doesn't change this. |
68dc0745 | 652 | |
5a964f20 TC |
653 | Here are examples of many kinds of file opens. Those using sysopen() |
654 | all assume | |
68dc0745 | 655 | |
500071f4 | 656 | use Fcntl; |
68dc0745 | 657 | |
5a964f20 | 658 | To open file for reading: |
68dc0745 | 659 | |
500071f4 RGS |
660 | open(FH, "< $path") || die $!; |
661 | sysopen(FH, $path, O_RDONLY) || die $!; | |
5a964f20 TC |
662 | |
663 | To open file for writing, create new file if needed or else truncate old file: | |
664 | ||
500071f4 RGS |
665 | open(FH, "> $path") || die $!; |
666 | sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT) || die $!; | |
667 | sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666) || die $!; | |
5a964f20 TC |
668 | |
669 | To open file for writing, create new file, file must not exist: | |
670 | ||
500071f4 RGS |
671 | sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT) || die $!; |
672 | sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT, 0666) || die $!; | |
5a964f20 TC |
673 | |
674 | To open file for appending, create if necessary: | |
675 | ||
500071f4 RGS |
676 | open(FH, ">> $path") || die $!; |
677 | sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT) || die $!; | |
678 | sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT, 0666) || die $!; | |
5a964f20 TC |
679 | |
680 | To open file for appending, file must exist: | |
681 | ||
500071f4 | 682 | sysopen(FH, $path, O_WRONLY|O_APPEND) || die $!; |
5a964f20 TC |
683 | |
684 | To open file for update, file must exist: | |
685 | ||
500071f4 RGS |
686 | open(FH, "+< $path") || die $!; |
687 | sysopen(FH, $path, O_RDWR) || die $!; | |
5a964f20 TC |
688 | |
689 | To open file for update, create file if necessary: | |
690 | ||
500071f4 RGS |
691 | sysopen(FH, $path, O_RDWR|O_CREAT) || die $!; |
692 | sysopen(FH, $path, O_RDWR|O_CREAT, 0666) || die $!; | |
5a964f20 TC |
693 | |
694 | To open file for update, file must not exist: | |
695 | ||
500071f4 RGS |
696 | sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT) || die $!; |
697 | sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT, 0666) || die $!; | |
5a964f20 TC |
698 | |
699 | To open a file without blocking, creating if necessary: | |
700 | ||
500071f4 | 701 | sysopen(FH, "/foo/somefile", O_WRONLY|O_NDELAY|O_CREAT) |
2359510d | 702 | or die "can't open /foo/somefile: $!": |
5a964f20 TC |
703 | |
704 | Be warned that neither creation nor deletion of files is guaranteed to | |
705 | be an atomic operation over NFS. That is, two processes might both | |
a6dd486b JB |
706 | successfully create or unlink the same file! Therefore O_EXCL |
707 | isn't as exclusive as you might wish. | |
68dc0745 | 708 | |
87275199 | 709 | See also the new L<perlopentut> if you have it (new for 5.6). |
65acb1b1 | 710 | |
04d666b1 | 711 | =head2 Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>? |
d74e8afc | 712 | X<argument list too long> |
68dc0745 | 713 | |
c47ff5f1 | 714 | The C<< <> >> operator performs a globbing operation (see above). |
3a4b19e4 GS |
715 | In Perl versions earlier than v5.6.0, the internal glob() operator forks |
716 | csh(1) to do the actual glob expansion, but | |
68dc0745 | 717 | csh can't handle more than 127 items and so gives the error message |
718 | C<Argument list too long>. People who installed tcsh as csh won't | |
719 | have this problem, but their users may be surprised by it. | |
720 | ||
3a4b19e4 | 721 | To get around this, either upgrade to Perl v5.6.0 or later, do the glob |
d6260402 | 722 | yourself with readdir() and patterns, or use a module like File::KGlob, |
3a4b19e4 | 723 | one that doesn't use the shell to do globbing. |
68dc0745 | 724 | |
725 | =head2 Is there a leak/bug in glob()? | |
d74e8afc | 726 | X<glob> |
68dc0745 | 727 | |
f12f5f55 | 728 | (conributed by brian d foy) |
729 | ||
730 | Starting with Perl 5.6.0, C<glob> is implemented internally rather | |
731 | than relying on an external resource. As such, memory issues with | |
732 | C<glob> aren't a problem in modern perls. | |
68dc0745 | 733 | |
c47ff5f1 | 734 | =head2 How can I open a file with a leading ">" or trailing blanks? |
d74e8afc | 735 | X<filename, special characters> |
68dc0745 | 736 | |
b68463f7 | 737 | (contributed by Brian McCauley) |
68dc0745 | 738 | |
b68463f7 RGS |
739 | The special two argument form of Perl's open() function ignores |
740 | trailing blanks in filenames and infers the mode from certain leading | |
741 | characters (or a trailing "|"). In older versions of Perl this was the | |
742 | only version of open() and so it is prevalent in old code and books. | |
65acb1b1 | 743 | |
b68463f7 RGS |
744 | Unless you have a particular reason to use the two argument form you |
745 | should use the three argument form of open() which does not treat any | |
c195e131 | 746 | characters in the filename as special. |
58103a2e | 747 | |
881bdbd4 JH |
748 | open FILE, "<", " file "; # filename is " file " |
749 | open FILE, ">", ">file"; # filename is ">file" | |
65acb1b1 | 750 | |
68dc0745 | 751 | =head2 How can I reliably rename a file? |
f12f5f55 | 752 | X<rename> X<mv> X<move> X<file, rename> |
68dc0745 | 753 | |
49d635f9 RGS |
754 | If your operating system supports a proper mv(1) utility or its |
755 | functional equivalent, this works: | |
68dc0745 | 756 | |
500071f4 | 757 | rename($old, $new) or system("mv", $old, $new); |
68dc0745 | 758 | |
f12f5f55 | 759 | It may be more portable to use the C<File::Copy> module instead. |
d2321c93 JH |
760 | You just copy to the new file to the new name (checking return |
761 | values), then delete the old one. This isn't really the same | |
f12f5f55 | 762 | semantically as a C<rename()>, which preserves meta-information like |
68dc0745 | 763 | permissions, timestamps, inode info, etc. |
764 | ||
765 | =head2 How can I lock a file? | |
d74e8afc | 766 | X<lock> X<file, lock> X<flock> |
68dc0745 | 767 | |
54310121 | 768 | Perl's builtin flock() function (see L<perlfunc> for details) will call |
68dc0745 | 769 | flock(2) if that exists, fcntl(2) if it doesn't (on perl version 5.004 and |
770 | later), and lockf(3) if neither of the two previous system calls exists. | |
771 | On some systems, it may even use a different form of native locking. | |
772 | Here are some gotchas with Perl's flock(): | |
773 | ||
774 | =over 4 | |
775 | ||
776 | =item 1 | |
777 | ||
778 | Produces a fatal error if none of the three system calls (or their | |
779 | close equivalent) exists. | |
780 | ||
781 | =item 2 | |
782 | ||
783 | lockf(3) does not provide shared locking, and requires that the | |
784 | filehandle be open for writing (or appending, or read/writing). | |
785 | ||
786 | =item 3 | |
787 | ||
d92eb7b0 GS |
788 | Some versions of flock() can't lock files over a network (e.g. on NFS file |
789 | systems), so you'd need to force the use of fcntl(2) when you build Perl. | |
a6dd486b | 790 | But even this is dubious at best. See the flock entry of L<perlfunc> |
d92eb7b0 GS |
791 | and the F<INSTALL> file in the source distribution for information on |
792 | building Perl to do this. | |
793 | ||
794 | Two potentially non-obvious but traditional flock semantics are that | |
a6dd486b | 795 | it waits indefinitely until the lock is granted, and that its locks are |
d92eb7b0 GS |
796 | I<merely advisory>. Such discretionary locks are more flexible, but |
797 | offer fewer guarantees. This means that files locked with flock() may | |
798 | be modified by programs that do not also use flock(). Cars that stop | |
799 | for red lights get on well with each other, but not with cars that don't | |
800 | stop for red lights. See the perlport manpage, your port's specific | |
801 | documentation, or your system-specific local manpages for details. It's | |
802 | best to assume traditional behavior if you're writing portable programs. | |
a6dd486b | 803 | (If you're not, you should as always feel perfectly free to write |
d92eb7b0 GS |
804 | for your own system's idiosyncrasies (sometimes called "features"). |
805 | Slavish adherence to portability concerns shouldn't get in the way of | |
806 | your getting your job done.) | |
68dc0745 | 807 | |
197aec24 | 808 | For more information on file locking, see also |
13a2d996 | 809 | L<perlopentut/"File Locking"> if you have it (new for 5.6). |
65acb1b1 | 810 | |
68dc0745 | 811 | =back |
812 | ||
04d666b1 | 813 | =head2 Why can't I just open(FH, "E<gt>file.lock")? |
d74e8afc | 814 | X<lock, lockfile race condition> |
68dc0745 | 815 | |
816 | A common bit of code B<NOT TO USE> is this: | |
817 | ||
500071f4 RGS |
818 | sleep(3) while -e "file.lock"; # PLEASE DO NOT USE |
819 | open(LCK, "> file.lock"); # THIS BROKEN CODE | |
68dc0745 | 820 | |
821 | This is a classic race condition: you take two steps to do something | |
822 | which must be done in one. That's why computer hardware provides an | |
823 | atomic test-and-set instruction. In theory, this "ought" to work: | |
824 | ||
500071f4 | 825 | sysopen(FH, "file.lock", O_WRONLY|O_EXCL|O_CREAT) |
9b55d3ab | 826 | or die "can't open file.lock: $!"; |
68dc0745 | 827 | |
828 | except that lamentably, file creation (and deletion) is not atomic | |
829 | over NFS, so this won't work (at least, not every time) over the net. | |
65acb1b1 | 830 | Various schemes involving link() have been suggested, but |
c195e131 | 831 | these tend to involve busy-wait, which is also less than desirable. |
68dc0745 | 832 | |
fc36a67e | 833 | =head2 I still don't get locking. I just want to increment the number in the file. How can I do this? |
d74e8afc | 834 | X<counter> X<file, counter> |
68dc0745 | 835 | |
46fc3d4c | 836 | Didn't anyone ever tell you web-page hit counters were useless? |
5a964f20 | 837 | They don't count number of hits, they're a waste of time, and they serve |
a6dd486b JB |
838 | only to stroke the writer's vanity. It's better to pick a random number; |
839 | they're more realistic. | |
68dc0745 | 840 | |
5a964f20 | 841 | Anyway, this is what you can do if you can't help yourself. |
68dc0745 | 842 | |
500071f4 RGS |
843 | use Fcntl qw(:DEFAULT :flock); |
844 | sysopen(FH, "numfile", O_RDWR|O_CREAT) or die "can't open numfile: $!"; | |
845 | flock(FH, LOCK_EX) or die "can't flock numfile: $!"; | |
846 | $num = <FH> || 0; | |
847 | seek(FH, 0, 0) or die "can't rewind numfile: $!"; | |
848 | truncate(FH, 0) or die "can't truncate numfile: $!"; | |
849 | (print FH $num+1, "\n") or die "can't write numfile: $!"; | |
850 | close FH or die "can't close numfile: $!"; | |
68dc0745 | 851 | |
46fc3d4c | 852 | Here's a much better web-page hit counter: |
68dc0745 | 853 | |
500071f4 | 854 | $hits = int( (time() - 850_000_000) / rand(1_000) ); |
68dc0745 | 855 | |
856 | If the count doesn't impress your friends, then the code might. :-) | |
857 | ||
f52f3be2 | 858 | =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? |
d74e8afc | 859 | X<append> X<file, append> |
05caf3a7 | 860 | |
109f0441 S |
861 | If you are on a system that correctly implements C<flock> and you use |
862 | the example appending code from "perldoc -f flock" everything will be | |
863 | OK even if the OS you are on doesn't implement append mode correctly | |
864 | (if such a system exists.) So if you are happy to restrict yourself to | |
865 | OSs that implement C<flock> (and that's not really much of a | |
866 | restriction) then that is what you should do. | |
05caf3a7 GJ |
867 | |
868 | If you know you are only going to use a system that does correctly | |
109f0441 S |
869 | implement appending (i.e. not Win32) then you can omit the C<seek> |
870 | from the code in the previous answer. | |
871 | ||
872 | If you know you are only writing code to run on an OS and filesystem | |
873 | that does implement append mode correctly (a local filesystem on a | |
874 | modern Unix for example), and you keep the file in block-buffered mode | |
875 | and you write less than one buffer-full of output between each manual | |
876 | flushing of the buffer then each bufferload is almost guaranteed to be | |
877 | written to the end of the file in one chunk without getting | |
878 | intermingled with anyone else's output. You can also use the | |
879 | C<syswrite> function which is simply a wrapper around your system's | |
880 | C<write(2)> system call. | |
05caf3a7 GJ |
881 | |
882 | There is still a small theoretical chance that a signal will interrupt | |
109f0441 S |
883 | the system level C<write()> operation before completion. There is also |
884 | a possibility that some STDIO implementations may call multiple system | |
885 | level C<write()>s even if the buffer was empty to start. There may be | |
886 | some systems where this probability is reduced to zero, and this is | |
887 | not a concern when using C<:perlio> instead of your system's STDIO. | |
05caf3a7 | 888 | |
68dc0745 | 889 | =head2 How do I randomly update a binary file? |
d74e8afc | 890 | X<file, binary patch> |
68dc0745 | 891 | |
892 | If you're just trying to patch a binary, in many cases something as | |
893 | simple as this works: | |
894 | ||
500071f4 | 895 | perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs |
68dc0745 | 896 | |
897 | However, if you have fixed sized records, then you might do something more | |
898 | like this: | |
899 | ||
500071f4 RGS |
900 | $RECSIZE = 220; # size of record, in bytes |
901 | $recno = 37; # which record to update | |
902 | open(FH, "+<somewhere") || die "can't update somewhere: $!"; | |
903 | seek(FH, $recno * $RECSIZE, 0); | |
904 | read(FH, $record, $RECSIZE) == $RECSIZE || die "can't read record $recno: $!"; | |
905 | # munge the record | |
906 | seek(FH, -$RECSIZE, 1); | |
907 | print FH $record; | |
908 | close FH; | |
68dc0745 | 909 | |
910 | Locking and error checking are left as an exercise for the reader. | |
a6dd486b | 911 | Don't forget them or you'll be quite sorry. |
68dc0745 | 912 | |
68dc0745 | 913 | =head2 How do I get a file's timestamp in perl? |
d74e8afc | 914 | X<timestamp> X<file, timestamp> |
68dc0745 | 915 | |
881bdbd4 JH |
916 | If you want to retrieve the time at which the file was last |
917 | read, written, or had its meta-data (owner, etc) changed, | |
a05e4845 | 918 | you use the B<-A>, B<-M>, or B<-C> file test operations as |
881bdbd4 JH |
919 | documented in L<perlfunc>. These retrieve the age of the |
920 | file (measured against the start-time of your program) in | |
921 | days as a floating point number. Some platforms may not have | |
922 | all of these times. See L<perlport> for details. To | |
923 | retrieve the "raw" time in seconds since the epoch, you | |
924 | would call the stat function, then use localtime(), | |
925 | gmtime(), or POSIX::strftime() to convert this into | |
926 | human-readable form. | |
68dc0745 | 927 | |
928 | Here's an example: | |
929 | ||
500071f4 RGS |
930 | $write_secs = (stat($file))[9]; |
931 | printf "file %s updated at %s\n", $file, | |
c8db1d39 | 932 | scalar localtime($write_secs); |
68dc0745 | 933 | |
934 | If you prefer something more legible, use the File::stat module | |
935 | (part of the standard distribution in version 5.004 and later): | |
936 | ||
500071f4 RGS |
937 | # error checking left as an exercise for reader. |
938 | use File::stat; | |
939 | use Time::localtime; | |
940 | $date_string = ctime(stat($file)->mtime); | |
941 | print "file $file updated at $date_string\n"; | |
68dc0745 | 942 | |
65acb1b1 TC |
943 | The POSIX::strftime() approach has the benefit of being, |
944 | in theory, independent of the current locale. See L<perllocale> | |
945 | for details. | |
68dc0745 | 946 | |
947 | =head2 How do I set a file's timestamp in perl? | |
d74e8afc | 948 | X<timestamp> X<file, timestamp> |
68dc0745 | 949 | |
950 | You use the utime() function documented in L<perlfunc/utime>. | |
951 | By way of example, here's a little program that copies the | |
952 | read and write times from its first argument to all the rest | |
953 | of them. | |
954 | ||
500071f4 RGS |
955 | if (@ARGV < 2) { |
956 | die "usage: cptimes timestamp_file other_files ...\n"; | |
957 | } | |
958 | $timestamp = shift; | |
959 | ($atime, $mtime) = (stat($timestamp))[8,9]; | |
960 | utime $atime, $mtime, @ARGV; | |
68dc0745 | 961 | |
65acb1b1 | 962 | Error checking is, as usual, left as an exercise for the reader. |
68dc0745 | 963 | |
19a1cd16 SP |
964 | The perldoc for utime also has an example that has the same |
965 | effect as touch(1) on files that I<already exist>. | |
966 | ||
967 | Certain file systems have a limited ability to store the times | |
968 | on a file at the expected level of precision. For example, the | |
969 | FAT and HPFS filesystem are unable to create dates on files with | |
970 | a finer granularity than two seconds. This is a limitation of | |
971 | the filesystems, not of utime(). | |
68dc0745 | 972 | |
973 | =head2 How do I print to more than one file at once? | |
d74e8afc | 974 | X<print, to multiple files> |
68dc0745 | 975 | |
49d635f9 RGS |
976 | To connect one filehandle to several output filehandles, |
977 | you can use the IO::Tee or Tie::FileHandle::Multiplex modules. | |
68dc0745 | 978 | |
49d635f9 RGS |
979 | If you only have to do this once, you can print individually |
980 | to each filehandle. | |
68dc0745 | 981 | |
500071f4 | 982 | for $fh (FH1, FH2, FH3) { print $fh "whatever\n" } |
5a964f20 | 983 | |
49d635f9 | 984 | =head2 How can I read in an entire file all at once? |
d74e8afc | 985 | X<slurp> X<file, slurping> |
68dc0745 | 986 | |
49d635f9 | 987 | You can use the File::Slurp module to do it in one step. |
68dc0745 | 988 | |
49d635f9 | 989 | use File::Slurp; |
197aec24 | 990 | |
49d635f9 | 991 | $all_of_it = read_file($filename); # entire file in scalar |
109f0441 | 992 | @all_lines = read_file($filename); # one line per element |
d92eb7b0 GS |
993 | |
994 | The customary Perl approach for processing all the lines in a file is to | |
995 | do so one line at a time: | |
996 | ||
500071f4 RGS |
997 | open (INPUT, $file) || die "can't open $file: $!"; |
998 | while (<INPUT>) { | |
999 | chomp; | |
1000 | # do something with $_ | |
1001 | } | |
1002 | close(INPUT) || die "can't close $file: $!"; | |
d92eb7b0 GS |
1003 | |
1004 | This is tremendously more efficient than reading the entire file into | |
1005 | memory as an array of lines and then processing it one element at a time, | |
a6dd486b | 1006 | which is often--if not almost always--the wrong approach. Whenever |
d92eb7b0 GS |
1007 | you see someone do this: |
1008 | ||
500071f4 | 1009 | @lines = <INPUT>; |
d92eb7b0 | 1010 | |
30852c57 JH |
1011 | you should think long and hard about why you need everything loaded at |
1012 | once. It's just not a scalable solution. You might also find it more | |
1013 | fun to use the standard Tie::File module, or the DB_File module's | |
1014 | $DB_RECNO bindings, which allow you to tie an array to a file so that | |
1015 | accessing an element the array actually accesses the corresponding | |
1016 | line in the file. | |
d92eb7b0 | 1017 | |
f05bbc40 | 1018 | You can read the entire filehandle contents into a scalar. |
d92eb7b0 | 1019 | |
500071f4 | 1020 | { |
d92eb7b0 GS |
1021 | local(*INPUT, $/); |
1022 | open (INPUT, $file) || die "can't open $file: $!"; | |
1023 | $var = <INPUT>; | |
500071f4 | 1024 | } |
d92eb7b0 | 1025 | |
197aec24 | 1026 | That temporarily undefs your record separator, and will automatically |
d92eb7b0 GS |
1027 | close the file at block exit. If the file is already open, just use this: |
1028 | ||
500071f4 | 1029 | $var = do { local $/; <INPUT> }; |
d92eb7b0 | 1030 | |
f05bbc40 JH |
1031 | For ordinary files you can also use the read function. |
1032 | ||
1033 | read( INPUT, $var, -s INPUT ); | |
1034 | ||
1035 | The third argument tests the byte size of the data on the INPUT filehandle | |
1036 | and reads that many bytes into the buffer $var. | |
1037 | ||
68dc0745 | 1038 | =head2 How can I read in a file by paragraphs? |
d74e8afc | 1039 | X<file, reading by paragraphs> |
68dc0745 | 1040 | |
65acb1b1 | 1041 | Use the C<$/> variable (see L<perlvar> for details). You can either |
68dc0745 | 1042 | set it to C<""> to eliminate empty paragraphs (C<"abc\n\n\n\ndef">, |
1043 | for instance, gets treated as two paragraphs and not three), or | |
1044 | C<"\n\n"> to accept empty paragraphs. | |
1045 | ||
197aec24 | 1046 | Note that a blank line must have no blanks in it. Thus |
c4db748a | 1047 | S<C<"fred\n \nstuff\n\n">> is one paragraph, but C<"fred\n\nstuff\n\n"> is two. |
65acb1b1 | 1048 | |
68dc0745 | 1049 | =head2 How can I read a single character from a file? From the keyboard? |
d74e8afc | 1050 | X<getc> X<file, reading one character at a time> |
68dc0745 | 1051 | |
1052 | You can use the builtin C<getc()> function for most filehandles, but | |
1053 | it won't (easily) work on a terminal device. For STDIN, either use | |
a6dd486b | 1054 | the Term::ReadKey module from CPAN or use the sample code in |
68dc0745 | 1055 | L<perlfunc/getc>. |
1056 | ||
65acb1b1 TC |
1057 | If your system supports the portable operating system programming |
1058 | interface (POSIX), you can use the following code, which you'll note | |
1059 | turns off echo processing as well. | |
68dc0745 | 1060 | |
500071f4 RGS |
1061 | #!/usr/bin/perl -w |
1062 | use strict; | |
1063 | $| = 1; | |
1064 | for (1..4) { | |
1065 | my $got; | |
1066 | print "gimme: "; | |
1067 | $got = getone(); | |
1068 | print "--> $got\n"; | |
1069 | } | |
68dc0745 | 1070 | exit; |
1071 | ||
500071f4 | 1072 | BEGIN { |
68dc0745 | 1073 | use POSIX qw(:termios_h); |
1074 | ||
1075 | my ($term, $oterm, $echo, $noecho, $fd_stdin); | |
1076 | ||
1077 | $fd_stdin = fileno(STDIN); | |
1078 | ||
1079 | $term = POSIX::Termios->new(); | |
1080 | $term->getattr($fd_stdin); | |
1081 | $oterm = $term->getlflag(); | |
1082 | ||
1083 | $echo = ECHO | ECHOK | ICANON; | |
1084 | $noecho = $oterm & ~$echo; | |
1085 | ||
1086 | sub cbreak { | |
500071f4 RGS |
1087 | $term->setlflag($noecho); |
1088 | $term->setcc(VTIME, 1); | |
1089 | $term->setattr($fd_stdin, TCSANOW); | |
1090 | } | |
ac9dac7f | 1091 | |
68dc0745 | 1092 | sub cooked { |
500071f4 RGS |
1093 | $term->setlflag($oterm); |
1094 | $term->setcc(VTIME, 0); | |
1095 | $term->setattr($fd_stdin, TCSANOW); | |
1096 | } | |
68dc0745 | 1097 | |
1098 | sub getone { | |
500071f4 RGS |
1099 | my $key = ''; |
1100 | cbreak(); | |
1101 | sysread(STDIN, $key, 1); | |
1102 | cooked(); | |
1103 | return $key; | |
1104 | } | |
68dc0745 | 1105 | |
500071f4 | 1106 | } |
68dc0745 | 1107 | |
500071f4 | 1108 | END { cooked() } |
68dc0745 | 1109 | |
a6dd486b | 1110 | The Term::ReadKey module from CPAN may be easier to use. Recent versions |
65acb1b1 | 1111 | include also support for non-portable systems as well. |
68dc0745 | 1112 | |
500071f4 RGS |
1113 | use Term::ReadKey; |
1114 | open(TTY, "</dev/tty"); | |
1115 | print "Gimme a char: "; | |
1116 | ReadMode "raw"; | |
1117 | $key = ReadKey 0, *TTY; | |
1118 | ReadMode "normal"; | |
1119 | printf "\nYou said %s, char number %03d\n", | |
1120 | $key, ord $key; | |
68dc0745 | 1121 | |
65acb1b1 | 1122 | =head2 How can I tell whether there's a character waiting on a filehandle? |
68dc0745 | 1123 | |
5a964f20 | 1124 | The very first thing you should do is look into getting the Term::ReadKey |
65acb1b1 TC |
1125 | extension from CPAN. As we mentioned earlier, it now even has limited |
1126 | support for non-portable (read: not open systems, closed, proprietary, | |
1127 | not POSIX, not Unix, etc) systems. | |
5a964f20 TC |
1128 | |
1129 | You should also check out the Frequently Asked Questions list in | |
68dc0745 | 1130 | comp.unix.* for things like this: the answer is essentially the same. |
1131 | It's very system dependent. Here's one solution that works on BSD | |
1132 | systems: | |
1133 | ||
500071f4 RGS |
1134 | sub key_ready { |
1135 | my($rin, $nfd); | |
1136 | vec($rin, fileno(STDIN), 1) = 1; | |
1137 | return $nfd = select($rin,undef,undef,0); | |
1138 | } | |
68dc0745 | 1139 | |
65acb1b1 TC |
1140 | If you want to find out how many characters are waiting, there's |
1141 | also the FIONREAD ioctl call to be looked at. The I<h2ph> tool that | |
1142 | comes with Perl tries to convert C include files to Perl code, which | |
1143 | can be C<require>d. FIONREAD ends up defined as a function in the | |
1144 | I<sys/ioctl.ph> file: | |
68dc0745 | 1145 | |
500071f4 | 1146 | require 'sys/ioctl.ph'; |
68dc0745 | 1147 | |
500071f4 RGS |
1148 | $size = pack("L", 0); |
1149 | ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n"; | |
1150 | $size = unpack("L", $size); | |
68dc0745 | 1151 | |
5a964f20 TC |
1152 | If I<h2ph> wasn't installed or doesn't work for you, you can |
1153 | I<grep> the include files by hand: | |
68dc0745 | 1154 | |
500071f4 RGS |
1155 | % grep FIONREAD /usr/include/*/* |
1156 | /usr/include/asm/ioctls.h:#define FIONREAD 0x541B | |
68dc0745 | 1157 | |
5a964f20 | 1158 | Or write a small C program using the editor of champions: |
68dc0745 | 1159 | |
500071f4 RGS |
1160 | % cat > fionread.c |
1161 | #include <sys/ioctl.h> | |
1162 | main() { | |
1163 | printf("%#08x\n", FIONREAD); | |
1164 | } | |
1165 | ^D | |
1166 | % cc -o fionread fionread.c | |
1167 | % ./fionread | |
1168 | 0x4004667f | |
5a964f20 | 1169 | |
8305e449 | 1170 | And then hard code it, leaving porting as an exercise to your successor. |
5a964f20 | 1171 | |
500071f4 | 1172 | $FIONREAD = 0x4004667f; # XXX: opsys dependent |
5a964f20 | 1173 | |
500071f4 RGS |
1174 | $size = pack("L", 0); |
1175 | ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n"; | |
1176 | $size = unpack("L", $size); | |
5a964f20 | 1177 | |
a6dd486b | 1178 | FIONREAD requires a filehandle connected to a stream, meaning that sockets, |
5a964f20 | 1179 | pipes, and tty devices work, but I<not> files. |
68dc0745 | 1180 | |
1181 | =head2 How do I do a C<tail -f> in perl? | |
ac9dac7f | 1182 | X<tail> X<IO::Handle> X<File::Tail> X<clearerr> |
68dc0745 | 1183 | |
1184 | First try | |
1185 | ||
500071f4 | 1186 | seek(GWFILE, 0, 1); |
68dc0745 | 1187 | |
1188 | The statement C<seek(GWFILE, 0, 1)> doesn't change the current position, | |
1189 | but it does clear the end-of-file condition on the handle, so that the | |
ac9dac7f | 1190 | next C<< <GWFILE> >> makes Perl try again to read something. |
68dc0745 | 1191 | |
1192 | If that doesn't work (it relies on features of your stdio implementation), | |
1193 | then you need something more like this: | |
1194 | ||
1195 | for (;;) { | |
1196 | for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE)) { | |
1197 | # search for some stuff and put it into files | |
1198 | } | |
1199 | # sleep for a while | |
1200 | seek(GWFILE, $curpos, 0); # seek to where we had been | |
1201 | } | |
1202 | ||
ac9dac7f RGS |
1203 | If this still doesn't work, look into the C<clearerr> method |
1204 | from C<IO::Handle>, which resets the error and end-of-file states | |
1205 | on the handle. | |
68dc0745 | 1206 | |
ac9dac7f | 1207 | There's also a C<File::Tail> module from CPAN. |
65acb1b1 | 1208 | |
68dc0745 | 1209 | =head2 How do I dup() a filehandle in Perl? |
d74e8afc | 1210 | X<dup> |
68dc0745 | 1211 | |
1212 | If you check L<perlfunc/open>, you'll see that several of the ways | |
1213 | to call open() should do the trick. For example: | |
1214 | ||
500071f4 RGS |
1215 | open(LOG, ">>/foo/logfile"); |
1216 | open(STDERR, ">&LOG"); | |
68dc0745 | 1217 | |
1218 | Or even with a literal numeric descriptor: | |
1219 | ||
1220 | $fd = $ENV{MHCONTEXTFD}; | |
1221 | open(MHCONTEXT, "<&=$fd"); # like fdopen(3S) | |
1222 | ||
c47ff5f1 | 1223 | Note that "<&STDIN" makes a copy, but "<&=STDIN" make |
5a964f20 | 1224 | an alias. That means if you close an aliased handle, all |
197aec24 | 1225 | aliases become inaccessible. This is not true with |
5a964f20 TC |
1226 | a copied one. |
1227 | ||
1228 | Error checking, as always, has been left as an exercise for the reader. | |
68dc0745 | 1229 | |
1230 | =head2 How do I close a file descriptor by number? | |
ee891a00 RGS |
1231 | X<file, closing file descriptors> X<POSIX> X<close> |
1232 | ||
1233 | If, for some reason, you have a file descriptor instead of a | |
1234 | filehandle (perhaps you used C<POSIX::open>), you can use the | |
1235 | C<close()> function from the C<POSIX> module: | |
68dc0745 | 1236 | |
ee891a00 | 1237 | use POSIX (); |
109f0441 | 1238 | |
ee891a00 | 1239 | POSIX::close( $fd ); |
109f0441 | 1240 | |
ac003c96 | 1241 | This should rarely be necessary, as the Perl C<close()> function is to be |
68dc0745 | 1242 | used for things that Perl opened itself, even if it was a dup of a |
ac003c96 | 1243 | numeric descriptor as with C<MHCONTEXT> above. But if you really have |
68dc0745 | 1244 | to, you may be able to do this: |
1245 | ||
500071f4 RGS |
1246 | require 'sys/syscall.ph'; |
1247 | $rc = syscall(&SYS_close, $fd + 0); # must force numeric | |
1248 | die "can't sysclose $fd: $!" unless $rc == -1; | |
68dc0745 | 1249 | |
ee891a00 | 1250 | Or, just use the fdopen(3S) feature of C<open()>: |
d92eb7b0 | 1251 | |
500071f4 | 1252 | { |
ee891a00 RGS |
1253 | open my( $fh ), "<&=$fd" or die "Cannot reopen fd=$fd: $!"; |
1254 | close $fh; | |
500071f4 | 1255 | } |
d92eb7b0 | 1256 | |
883f1635 | 1257 | =head2 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work? |
d74e8afc | 1258 | X<filename, DOS issues> |
68dc0745 | 1259 | |
1260 | Whoops! You just put a tab and a formfeed into that filename! | |
1261 | Remember that within double quoted strings ("like\this"), the | |
1262 | backslash is an escape character. The full list of these is in | |
1263 | L<perlop/Quote and Quote-like Operators>. Unsurprisingly, you don't | |
1264 | have a file called "c:(tab)emp(formfeed)oo" or | |
65acb1b1 | 1265 | "c:(tab)emp(formfeed)oo.exe" on your legacy DOS filesystem. |
68dc0745 | 1266 | |
1267 | Either single-quote your strings, or (preferably) use forward slashes. | |
46fc3d4c | 1268 | Since all DOS and Windows versions since something like MS-DOS 2.0 or so |
68dc0745 | 1269 | have treated C</> and C<\> the same in a path, you might as well use the |
a6dd486b | 1270 | one that doesn't clash with Perl--or the POSIX shell, ANSI C and C++, |
65acb1b1 TC |
1271 | awk, Tcl, Java, or Python, just to mention a few. POSIX paths |
1272 | are more portable, too. | |
68dc0745 | 1273 | |
1274 | =head2 Why doesn't glob("*.*") get all the files? | |
d74e8afc | 1275 | X<glob> |
68dc0745 | 1276 | |
1277 | Because even on non-Unix ports, Perl's glob function follows standard | |
46fc3d4c | 1278 | Unix globbing semantics. You'll need C<glob("*")> to get all (non-hidden) |
65acb1b1 TC |
1279 | files. This makes glob() portable even to legacy systems. Your |
1280 | port may include proprietary globbing functions as well. Check its | |
1281 | documentation for details. | |
68dc0745 | 1282 | |
1283 | =head2 Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl? | |
1284 | ||
06a5f41f JH |
1285 | This is elaborately and painstakingly described in the |
1286 | F<file-dir-perms> article in the "Far More Than You Ever Wanted To | |
49d635f9 | 1287 | Know" collection in http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz . |
68dc0745 | 1288 | |
1289 | The executive summary: learn how your filesystem works. The | |
1290 | permissions on a file say what can happen to the data in that file. | |
1291 | The permissions on a directory say what can happen to the list of | |
1292 | files in that directory. If you delete a file, you're removing its | |
1293 | name from the directory (so the operation depends on the permissions | |
1294 | of the directory, not of the file). If you try to write to the file, | |
1295 | the permissions of the file govern whether you're allowed to. | |
1296 | ||
1297 | =head2 How do I select a random line from a file? | |
d74e8afc | 1298 | X<file, selecting a random line> |
68dc0745 | 1299 | |
109f0441 S |
1300 | Short of loading the file into a database or pre-indexing the lines in |
1301 | the file, there are a couple of things that you can do. | |
1302 | ||
1303 | Here's a reservoir-sampling algorithm from the Camel Book: | |
68dc0745 | 1304 | |
500071f4 RGS |
1305 | srand; |
1306 | rand($.) < 1 && ($line = $_) while <>; | |
68dc0745 | 1307 | |
49d635f9 RGS |
1308 | This has a significant advantage in space over reading the whole file |
1309 | in. You can find a proof of this method in I<The Art of Computer | |
1310 | Programming>, Volume 2, Section 3.4.2, by Donald E. Knuth. | |
1311 | ||
109f0441 | 1312 | You can use the C<File::Random> module which provides a function |
49d635f9 RGS |
1313 | for that algorithm: |
1314 | ||
1315 | use File::Random qw/random_line/; | |
1316 | my $line = random_line($filename); | |
1317 | ||
109f0441 | 1318 | Another way is to use the C<Tie::File> module, which treats the entire |
49d635f9 | 1319 | file as an array. Simply access a random array element. |
68dc0745 | 1320 | |
65acb1b1 TC |
1321 | =head2 Why do I get weird spaces when I print an array of lines? |
1322 | ||
109f0441 S |
1323 | (contributed by brian d foy) |
1324 | ||
1325 | If you are seeing spaces between the elements of your array when | |
1326 | you print the array, you are probably interpolating the array in | |
1327 | double quotes: | |
1328 | ||
1329 | my @animals = qw(camel llama alpaca vicuna); | |
1330 | print "animals are: @animals\n"; | |
65acb1b1 | 1331 | |
109f0441 S |
1332 | It's the double quotes, not the C<print>, doing this. Whenever you |
1333 | interpolate an array in a double quote context, Perl joins the | |
1334 | elements with spaces (or whatever is in C<$">, which is a space by | |
1335 | default): | |
65acb1b1 | 1336 | |
109f0441 | 1337 | animals are: camel llama alpaca vicuna |
65acb1b1 | 1338 | |
109f0441 | 1339 | This is different than printing the array without the interpolation: |
65acb1b1 | 1340 | |
109f0441 S |
1341 | my @animals = qw(camel llama alpaca vicuna); |
1342 | print "animals are: ", @animals, "\n"; | |
65acb1b1 | 1343 | |
109f0441 S |
1344 | Now the output doesn't have the spaces between the elements because |
1345 | the elements of C<@animals> simply become part of the list to | |
1346 | C<print>: | |
65acb1b1 | 1347 | |
109f0441 S |
1348 | animals are: camelllamaalpacavicuna |
1349 | ||
1350 | You might notice this when each of the elements of C<@array> end with | |
1351 | a newline. You expect to print one element per line, but notice that | |
1352 | every line after the first is indented: | |
1353 | ||
1354 | this is a line | |
1355 | this is another line | |
1356 | this is the third line | |
1357 | ||
1358 | That extra space comes from the interpolation of the array. If you | |
1359 | don't want to put anything between your array elements, don't use the | |
1360 | array in double quotes. You can send it to print without them: | |
65acb1b1 | 1361 | |
500071f4 RGS |
1362 | print @lines; |
1363 | ||
109f0441 S |
1364 | =head2 How do I traverse a directory tree? |
1365 | ||
1366 | (contributed by brian d foy) | |
1367 | ||
1368 | The C<File::Find> module, which comes with Perl, does all of the hard | |
1369 | work to traverse a directory structure. It comes with Perl. You simply | |
1370 | call the C<find> subroutine with a callback subroutine and the | |
1371 | directories you want to traverse: | |
1372 | ||
1373 | use File::Find; | |
1374 | ||
1375 | find( \&wanted, @directories ); | |
1376 | ||
1377 | sub wanted { | |
1378 | # full path in $File::Find::name | |
1379 | # just filename in $_ | |
1380 | ... do whatever you want to do ... | |
1381 | } | |
1382 | ||
1383 | The C<File::Find::Closures>, which you can download from CPAN, provides | |
1384 | many ready-to-use subroutines that you can use with C<File::Find>. | |
1385 | ||
1386 | The C<File::Finder>, which you can download from CPAN, can help you | |
1387 | create the callback subroutine using something closer to the syntax of | |
1388 | the C<find> command-line utility: | |
1389 | ||
1390 | use File::Find; | |
1391 | use File::Finder; | |
1392 | ||
1393 | my $deep_dirs = File::Finder->depth->type('d')->ls->exec('rmdir','{}'); | |
1394 | ||
1395 | find( $deep_dirs->as_options, @places ); | |
1396 | ||
1397 | The C<File::Find::Rule> module, which you can download from CPAN, has | |
1398 | a similar interface, but does the traversal for you too: | |
1399 | ||
1400 | use File::Find::Rule; | |
1401 | ||
1402 | my @files = File::Find::Rule->file() | |
1403 | ->name( '*.pm' ) | |
1404 | ->in( @INC ); | |
1405 | ||
1406 | =head2 How do I delete a directory tree? | |
1407 | ||
1408 | (contributed by brian d foy) | |
1409 | ||
1410 | If you have an empty directory, you can use Perl's built-in C<rmdir>. If | |
1411 | the directory is not empty (so, no files or subdirectories), you either | |
1412 | have to empty it yourself (a lot of work) or use a module to help you. | |
1413 | ||
1414 | The C<File::Path> module, which comes with Perl, has a C<rmtree> which | |
1415 | can take care of all of the hard work for you: | |
1416 | ||
1417 | use File::Path qw(rmtree); | |
1418 | ||
1419 | rmtree( \@directories, 0, 0 ); | |
1420 | ||
1421 | The first argument to C<rmtree> is either a string representing a directory path | |
1422 | or an array reference. The second argument controls progress messages, and the | |
1423 | third argument controls the handling of files you don't have permissions to | |
1424 | delete. See the C<File::Path> module for the details. | |
1425 | ||
1426 | =head2 How do I copy an entire directory? | |
1427 | ||
1428 | (contributed by Shlomi Fish) | |
1429 | ||
1430 | To do the equivalent of C<cp -R> (i.e. copy an entire directory tree | |
1431 | recursively) in portable Perl, you'll either need to write something yourself | |
1432 | or find a good CPAN module such as L<File::Copy::Recursive>. | |
500071f4 RGS |
1433 | =head1 REVISION |
1434 | ||
109f0441 | 1435 | Revision: $Revision$ |
500071f4 | 1436 | |
109f0441 | 1437 | Date: $Date$ |
500071f4 RGS |
1438 | |
1439 | See L<perlfaq> for source control details and availability. | |
65acb1b1 | 1440 | |
68dc0745 | 1441 | =head1 AUTHOR AND COPYRIGHT |
1442 | ||
109f0441 | 1443 | Copyright (c) 1997-2009 Tom Christiansen, Nathan Torkington, and |
7678cced | 1444 | other authors as noted. All rights reserved. |
5a964f20 | 1445 | |
5a7beb56 JH |
1446 | This documentation is free; you can redistribute it and/or modify it |
1447 | under the same terms as Perl itself. | |
c8db1d39 | 1448 | |
87275199 | 1449 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 TC |
1450 | domain. You are permitted and encouraged to use this code and any |
1451 | derivatives thereof in your own programs for fun or for profit as you | |
1452 | see fit. A simple comment in the code giving credit to the FAQ would | |
1453 | be courteous but is not required. |