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1 | =head1 NAME |
2 | ||
3 | perlfaq5 - Files and Formats ($Revision: 1.42 $, $Date: 2005/12/31 00:54:37 $) | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | This section deals with I/O and the "f" issues: filehandles, flushing, | |
8 | formats, and footers. | |
9 | ||
10 | =head2 How do I flush/unbuffer an output filehandle? Why must I do this? | |
11 | X<flush> X<buffer> X<unbuffer> X<autoflush> | |
12 | ||
13 | Perl does not support truly unbuffered output (except | |
14 | insofar as you can C<syswrite(OUT, $char, 1)>), although it | |
15 | does support is "command buffering", in which a physical | |
16 | write is performed after every output command. | |
17 | ||
18 | The C standard I/O library (stdio) normally buffers | |
19 | characters sent to devices so that there isn't a system call | |
20 | for each byte. In most stdio implementations, the type of | |
21 | output buffering and the size of the buffer varies according | |
22 | to the type of device. Perl's print() and write() functions | |
23 | normally buffer output, while syswrite() bypasses buffering | |
24 | all together. | |
25 | ||
26 | If you want your output to be sent immediately when you | |
27 | execute print() or write() (for instance, for some network | |
28 | protocols), you must set the handle's autoflush flag. This | |
29 | flag is the Perl variable $| and when it is set to a true | |
30 | value, Perl will flush the handle's buffer after each | |
31 | print() or write(). Setting $| affects buffering only for | |
32 | the currently selected default file handle. You choose this | |
33 | handle with the one argument select() call (see | |
34 | L<perlvar/$E<verbar>> and L<perlfunc/select>). | |
35 | ||
36 | Use select() to choose the desired handle, then set its | |
37 | per-filehandle variables. | |
38 | ||
39 | $old_fh = select(OUTPUT_HANDLE); | |
40 | $| = 1; | |
41 | select($old_fh); | |
42 | ||
43 | Some idioms can handle this in a single statement: | |
44 | ||
45 | select((select(OUTPUT_HANDLE), $| = 1)[0]); | |
46 | ||
47 | $| = 1, select $_ for select OUTPUT_HANDLE; | |
48 | ||
49 | Some modules offer object-oriented access to handles and their | |
50 | variables, although they may be overkill if this is the only | |
51 | thing you do with them. You can use IO::Handle: | |
52 | ||
53 | use IO::Handle; | |
54 | open(DEV, ">/dev/printer"); # but is this? | |
55 | DEV->autoflush(1); | |
56 | ||
57 | or IO::Socket: | |
58 | ||
59 | use IO::Socket; # this one is kinda a pipe? | |
60 | my $sock = IO::Socket::INET->new( 'www.example.com:80' ); | |
61 | ||
62 | $sock->autoflush(); | |
63 | ||
64 | =head2 How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? | |
65 | X<file, editing> | |
66 | ||
67 | Use the Tie::File module, which is included in the standard | |
68 | distribution since Perl 5.8.0. | |
69 | ||
70 | =head2 How do I count the number of lines in a file? | |
71 | X<file, counting lines> X<lines> X<line> | |
72 | ||
73 | One fairly efficient way is to count newlines in the file. The | |
74 | following program uses a feature of tr///, as documented in L<perlop>. | |
75 | If your text file doesn't end with a newline, then it's not really a | |
76 | proper text file, so this may report one fewer line than you expect. | |
77 | ||
78 | $lines = 0; | |
79 | open(FILE, $filename) or die "Can't open `$filename': $!"; | |
80 | while (sysread FILE, $buffer, 4096) { | |
81 | $lines += ($buffer =~ tr/\n//); | |
82 | } | |
83 | close FILE; | |
84 | ||
85 | This assumes no funny games with newline translations. | |
86 | ||
87 | =head2 How can I use Perl's C<-i> option from within a program? | |
88 | X<-i> X<in-place> | |
89 | ||
90 | C<-i> sets the value of Perl's C<$^I> variable, which in turn affects | |
91 | the behavior of C<< <> >>; see L<perlrun> for more details. By | |
92 | modifying the appropriate variables directly, you can get the same | |
93 | behavior within a larger program. For example: | |
94 | ||
95 | # ... | |
96 | { | |
97 | local($^I, @ARGV) = ('.orig', glob("*.c")); | |
98 | while (<>) { | |
99 | if ($. == 1) { | |
100 | print "This line should appear at the top of each file\n"; | |
101 | } | |
102 | s/\b(p)earl\b/${1}erl/i; # Correct typos, preserving case | |
103 | print; | |
104 | close ARGV if eof; # Reset $. | |
105 | } | |
106 | } | |
107 | # $^I and @ARGV return to their old values here | |
108 | ||
109 | This block modifies all the C<.c> files in the current directory, | |
110 | leaving a backup of the original data from each file in a new | |
111 | C<.c.orig> file. | |
112 | ||
113 | =head2 How can I copy a file? | |
114 | X<copy> X<file, copy> | |
115 | ||
116 | (contributed by brian d foy) | |
117 | ||
118 | Use the File::Copy module. It comes with Perl and can do a | |
119 | true copy across file systems, and it does its magic in | |
120 | a portable fashion. | |
121 | ||
122 | use File::Copy; | |
123 | ||
124 | copy( $original, $new_copy ) or die "Copy failed: $!"; | |
125 | ||
126 | If you can't use File::Copy, you'll have to do the work yourself: | |
127 | open the original file, open the destination file, then print | |
128 | to the destination file as you read the original. | |
129 | ||
130 | =head2 How do I make a temporary file name? | |
131 | X<file, temporary> | |
132 | ||
133 | If you don't need to know the name of the file, you can use C<open()> | |
134 | with C<undef> in place of the file name. The C<open()> function | |
135 | creates an anonymous temporary file. | |
136 | ||
137 | open my $tmp, '+>', undef or die $!; | |
138 | ||
139 | Otherwise, you can use the File::Temp module. | |
140 | ||
141 | use File::Temp qw/ tempfile tempdir /; | |
142 | ||
143 | $dir = tempdir( CLEANUP => 1 ); | |
144 | ($fh, $filename) = tempfile( DIR => $dir ); | |
145 | ||
146 | # or if you don't need to know the filename | |
147 | ||
148 | $fh = tempfile( DIR => $dir ); | |
149 | ||
150 | The File::Temp has been a standard module since Perl 5.6.1. If you | |
151 | don't have a modern enough Perl installed, use the C<new_tmpfile> | |
152 | class method from the IO::File module to get a filehandle opened for | |
153 | reading and writing. Use it if you don't need to know the file's name: | |
154 | ||
155 | use IO::File; | |
156 | $fh = IO::File->new_tmpfile() | |
157 | or die "Unable to make new temporary file: $!"; | |
158 | ||
159 | If you're committed to creating a temporary file by hand, use the | |
160 | process ID and/or the current time-value. If you need to have many | |
161 | temporary files in one process, use a counter: | |
162 | ||
163 | BEGIN { | |
164 | use Fcntl; | |
165 | my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMPDIR} || $ENV{TEMP}; | |
166 | my $base_name = sprintf("%s/%d-%d-0000", $temp_dir, $$, time()); | |
167 | sub temp_file { | |
168 | local *FH; | |
169 | my $count = 0; | |
170 | until (defined(fileno(FH)) || $count++ > 100) { | |
171 | $base_name =~ s/-(\d+)$/"-" . (1 + $1)/e; | |
172 | # O_EXCL is required for security reasons. | |
173 | sysopen(FH, $base_name, O_WRONLY|O_EXCL|O_CREAT); | |
174 | } | |
175 | if (defined(fileno(FH)) | |
176 | return (*FH, $base_name); | |
177 | } else { | |
178 | return (); | |
179 | } | |
180 | } | |
181 | } | |
182 | ||
183 | =head2 How can I manipulate fixed-record-length files? | |
184 | X<fixed-length> X<file, fixed-length records> | |
185 | ||
186 | The most efficient way is using L<pack()|perlfunc/"pack"> and | |
187 | L<unpack()|perlfunc/"unpack">. This is faster than using | |
188 | L<substr()|perlfunc/"substr"> when taking many, many strings. It is | |
189 | slower for just a few. | |
190 | ||
191 | Here is a sample chunk of code to break up and put back together again | |
192 | some fixed-format input lines, in this case from the output of a normal, | |
193 | Berkeley-style ps: | |
194 | ||
195 | # sample input line: | |
196 | # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what | |
197 | my $PS_T = 'A6 A4 A7 A5 A*'; | |
198 | open my $ps, '-|', 'ps'; | |
199 | print scalar <$ps>; | |
200 | my @fields = qw( pid tt stat time command ); | |
201 | while (<$ps>) { | |
202 | my %process; | |
203 | @process{@fields} = unpack($PS_T, $_); | |
204 | for my $field ( @fields ) { | |
205 | print "$field: <$process{$field}>\n"; | |
206 | } | |
207 | print 'line=', pack($PS_T, @process{@fields} ), "\n"; | |
208 | } | |
209 | ||
210 | We've used a hash slice in order to easily handle the fields of each row. | |
211 | Storing the keys in an array means it's easy to operate on them as a | |
212 | group or loop over them with for. It also avoids polluting the program | |
213 | with global variables and using symbolic references. | |
214 | ||
215 | =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? | |
216 | X<filehandle, local> X<filehandle, passing> X<filehandle, reference> | |
217 | ||
218 | As of perl5.6, open() autovivifies file and directory handles | |
219 | as references if you pass it an uninitialized scalar variable. | |
220 | You can then pass these references just like any other scalar, | |
221 | and use them in the place of named handles. | |
222 | ||
223 | open my $fh, $file_name; | |
224 | ||
225 | open local $fh, $file_name; | |
226 | ||
227 | print $fh "Hello World!\n"; | |
228 | ||
229 | process_file( $fh ); | |
230 | ||
231 | Before perl5.6, you had to deal with various typeglob idioms | |
232 | which you may see in older code. | |
233 | ||
234 | open FILE, "> $filename"; | |
235 | process_typeglob( *FILE ); | |
236 | process_reference( \*FILE ); | |
237 | ||
238 | sub process_typeglob { local *FH = shift; print FH "Typeglob!" } | |
239 | sub process_reference { local $fh = shift; print $fh "Reference!" } | |
240 | ||
241 | If you want to create many anonymous handles, you should | |
242 | check out the Symbol or IO::Handle modules. | |
243 | ||
244 | =head2 How can I use a filehandle indirectly? | |
245 | X<filehandle, indirect> | |
246 | ||
247 | An indirect filehandle is using something other than a symbol | |
248 | in a place that a filehandle is expected. Here are ways | |
249 | to get indirect filehandles: | |
250 | ||
251 | $fh = SOME_FH; # bareword is strict-subs hostile | |
252 | $fh = "SOME_FH"; # strict-refs hostile; same package only | |
253 | $fh = *SOME_FH; # typeglob | |
254 | $fh = \*SOME_FH; # ref to typeglob (bless-able) | |
255 | $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob | |
256 | ||
257 | Or, you can use the C<new> method from one of the IO::* modules to | |
258 | create an anonymous filehandle, store that in a scalar variable, | |
259 | and use it as though it were a normal filehandle. | |
260 | ||
261 | use IO::Handle; # 5.004 or higher | |
262 | $fh = IO::Handle->new(); | |
263 | ||
264 | Then use any of those as you would a normal filehandle. Anywhere that | |
265 | Perl is expecting a filehandle, an indirect filehandle may be used | |
266 | instead. An indirect filehandle is just a scalar variable that contains | |
267 | a filehandle. Functions like C<print>, C<open>, C<seek>, or | |
268 | the C<< <FH> >> diamond operator will accept either a named filehandle | |
269 | or a scalar variable containing one: | |
270 | ||
271 | ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR); | |
272 | print $ofh "Type it: "; | |
273 | $got = <$ifh> | |
274 | print $efh "What was that: $got"; | |
275 | ||
276 | If you're passing a filehandle to a function, you can write | |
277 | the function in two ways: | |
278 | ||
279 | sub accept_fh { | |
280 | my $fh = shift; | |
281 | print $fh "Sending to indirect filehandle\n"; | |
282 | } | |
283 | ||
284 | Or it can localize a typeglob and use the filehandle directly: | |
285 | ||
286 | sub accept_fh { | |
287 | local *FH = shift; | |
288 | print FH "Sending to localized filehandle\n"; | |
289 | } | |
290 | ||
291 | Both styles work with either objects or typeglobs of real filehandles. | |
292 | (They might also work with strings under some circumstances, but this | |
293 | is risky.) | |
294 | ||
295 | accept_fh(*STDOUT); | |
296 | accept_fh($handle); | |
297 | ||
298 | In the examples above, we assigned the filehandle to a scalar variable | |
299 | before using it. That is because only simple scalar variables, not | |
300 | expressions or subscripts of hashes or arrays, can be used with | |
301 | built-ins like C<print>, C<printf>, or the diamond operator. Using | |
302 | something other than a simple scalar variable as a filehandle is | |
303 | illegal and won't even compile: | |
304 | ||
305 | @fd = (*STDIN, *STDOUT, *STDERR); | |
306 | print $fd[1] "Type it: "; # WRONG | |
307 | $got = <$fd[0]> # WRONG | |
308 | print $fd[2] "What was that: $got"; # WRONG | |
309 | ||
310 | With C<print> and C<printf>, you get around this by using a block and | |
311 | an expression where you would place the filehandle: | |
312 | ||
313 | print { $fd[1] } "funny stuff\n"; | |
314 | printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559; | |
315 | # Pity the poor deadbeef. | |
316 | ||
317 | That block is a proper block like any other, so you can put more | |
318 | complicated code there. This sends the message out to one of two places: | |
319 | ||
320 | $ok = -x "/bin/cat"; | |
321 | print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n"; | |
322 | print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n"; | |
323 | ||
324 | This approach of treating C<print> and C<printf> like object methods | |
325 | calls doesn't work for the diamond operator. That's because it's a | |
326 | real operator, not just a function with a comma-less argument. Assuming | |
327 | you've been storing typeglobs in your structure as we did above, you | |
328 | can use the built-in function named C<readline> to read a record just | |
329 | as C<< <> >> does. Given the initialization shown above for @fd, this | |
330 | would work, but only because readline() requires a typeglob. It doesn't | |
331 | work with objects or strings, which might be a bug we haven't fixed yet. | |
332 | ||
333 | $got = readline($fd[0]); | |
334 | ||
335 | Let it be noted that the flakiness of indirect filehandles is not | |
336 | related to whether they're strings, typeglobs, objects, or anything else. | |
337 | It's the syntax of the fundamental operators. Playing the object | |
338 | game doesn't help you at all here. | |
339 | ||
340 | =head2 How can I set up a footer format to be used with write()? | |
341 | X<footer> | |
342 | ||
343 | There's no builtin way to do this, but L<perlform> has a couple of | |
344 | techniques to make it possible for the intrepid hacker. | |
345 | ||
346 | =head2 How can I write() into a string? | |
347 | X<write, into a string> | |
348 | ||
349 | See L<perlform/"Accessing Formatting Internals"> for an swrite() function. | |
350 | ||
351 | =head2 How can I output my numbers with commas added? | |
352 | X<number, commify> | |
353 | ||
354 | (contributed by brian d foy and Benjamin Goldberg) | |
355 | ||
356 | You can use L<Number::Format> to separate places in a number. | |
357 | It handles locale information for those of you who want to insert | |
358 | full stops instead (or anything else that they want to use, | |
359 | really). | |
360 | ||
361 | This subroutine will add commas to your number: | |
362 | ||
363 | sub commify { | |
364 | local $_ = shift; | |
365 | 1 while s/^([-+]?\d+)(\d{3})/$1,$2/; | |
366 | return $_; | |
367 | } | |
368 | ||
369 | This regex from Benjamin Goldberg will add commas to numbers: | |
370 | ||
371 | s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g; | |
372 | ||
373 | It is easier to see with comments: | |
374 | ||
375 | s/( | |
376 | ^[-+]? # beginning of number. | |
377 | \d+? # first digits before first comma | |
378 | (?= # followed by, (but not included in the match) : | |
379 | (?>(?:\d{3})+) # some positive multiple of three digits. | |
380 | (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever. | |
381 | ) | |
382 | | # or: | |
383 | \G\d{3} # after the last group, get three digits | |
384 | (?=\d) # but they have to have more digits after them. | |
385 | )/$1,/xg; | |
386 | ||
387 | =head2 How can I translate tildes (~) in a filename? | |
388 | X<tilde> X<tilde expansion> | |
389 | ||
390 | Use the <> (glob()) operator, documented in L<perlfunc>. Older | |
391 | versions of Perl require that you have a shell installed that groks | |
392 | tildes. Recent perl versions have this feature built in. The | |
393 | File::KGlob module (available from CPAN) gives more portable glob | |
394 | functionality. | |
395 | ||
396 | Within Perl, you may use this directly: | |
397 | ||
398 | $filename =~ s{ | |
399 | ^ ~ # find a leading tilde | |
400 | ( # save this in $1 | |
401 | [^/] # a non-slash character | |
402 | * # repeated 0 or more times (0 means me) | |
403 | ) | |
404 | }{ | |
405 | $1 | |
406 | ? (getpwnam($1))[7] | |
407 | : ( $ENV{HOME} || $ENV{LOGDIR} ) | |
408 | }ex; | |
409 | ||
410 | =head2 How come when I open a file read-write it wipes it out? | |
411 | X<clobber> X<read-write> X<clobbering> X<truncate> X<truncating> | |
412 | ||
413 | Because you're using something like this, which truncates the file and | |
414 | I<then> gives you read-write access: | |
415 | ||
416 | open(FH, "+> /path/name"); # WRONG (almost always) | |
417 | ||
418 | Whoops. You should instead use this, which will fail if the file | |
419 | doesn't exist. | |
420 | ||
421 | open(FH, "+< /path/name"); # open for update | |
422 | ||
423 | Using ">" always clobbers or creates. Using "<" never does | |
424 | either. The "+" doesn't change this. | |
425 | ||
426 | Here are examples of many kinds of file opens. Those using sysopen() | |
427 | all assume | |
428 | ||
429 | use Fcntl; | |
430 | ||
431 | To open file for reading: | |
432 | ||
433 | open(FH, "< $path") || die $!; | |
434 | sysopen(FH, $path, O_RDONLY) || die $!; | |
435 | ||
436 | To open file for writing, create new file if needed or else truncate old file: | |
437 | ||
438 | open(FH, "> $path") || die $!; | |
439 | sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT) || die $!; | |
440 | sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666) || die $!; | |
441 | ||
442 | To open file for writing, create new file, file must not exist: | |
443 | ||
444 | sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT) || die $!; | |
445 | sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT, 0666) || die $!; | |
446 | ||
447 | To open file for appending, create if necessary: | |
448 | ||
449 | open(FH, ">> $path") || die $!; | |
450 | sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT) || die $!; | |
451 | sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT, 0666) || die $!; | |
452 | ||
453 | To open file for appending, file must exist: | |
454 | ||
455 | sysopen(FH, $path, O_WRONLY|O_APPEND) || die $!; | |
456 | ||
457 | To open file for update, file must exist: | |
458 | ||
459 | open(FH, "+< $path") || die $!; | |
460 | sysopen(FH, $path, O_RDWR) || die $!; | |
461 | ||
462 | To open file for update, create file if necessary: | |
463 | ||
464 | sysopen(FH, $path, O_RDWR|O_CREAT) || die $!; | |
465 | sysopen(FH, $path, O_RDWR|O_CREAT, 0666) || die $!; | |
466 | ||
467 | To open file for update, file must not exist: | |
468 | ||
469 | sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT) || die $!; | |
470 | sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT, 0666) || die $!; | |
471 | ||
472 | To open a file without blocking, creating if necessary: | |
473 | ||
474 | sysopen(FH, "/foo/somefile", O_WRONLY|O_NDELAY|O_CREAT) | |
475 | or die "can't open /foo/somefile: $!": | |
476 | ||
477 | Be warned that neither creation nor deletion of files is guaranteed to | |
478 | be an atomic operation over NFS. That is, two processes might both | |
479 | successfully create or unlink the same file! Therefore O_EXCL | |
480 | isn't as exclusive as you might wish. | |
481 | ||
482 | See also the new L<perlopentut> if you have it (new for 5.6). | |
483 | ||
484 | =head2 Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>? | |
485 | X<argument list too long> | |
486 | ||
487 | The C<< <> >> operator performs a globbing operation (see above). | |
488 | In Perl versions earlier than v5.6.0, the internal glob() operator forks | |
489 | csh(1) to do the actual glob expansion, but | |
490 | csh can't handle more than 127 items and so gives the error message | |
491 | C<Argument list too long>. People who installed tcsh as csh won't | |
492 | have this problem, but their users may be surprised by it. | |
493 | ||
494 | To get around this, either upgrade to Perl v5.6.0 or later, do the glob | |
495 | yourself with readdir() and patterns, or use a module like File::KGlob, | |
496 | one that doesn't use the shell to do globbing. | |
497 | ||
498 | =head2 Is there a leak/bug in glob()? | |
499 | X<glob> | |
500 | ||
501 | Due to the current implementation on some operating systems, when you | |
502 | use the glob() function or its angle-bracket alias in a scalar | |
503 | context, you may cause a memory leak and/or unpredictable behavior. It's | |
504 | best therefore to use glob() only in list context. | |
505 | ||
506 | =head2 How can I open a file with a leading ">" or trailing blanks? | |
507 | X<filename, special characters> | |
508 | ||
509 | (contributed by Brian McCauley) | |
510 | ||
511 | The special two argument form of Perl's open() function ignores | |
512 | trailing blanks in filenames and infers the mode from certain leading | |
513 | characters (or a trailing "|"). In older versions of Perl this was the | |
514 | only version of open() and so it is prevalent in old code and books. | |
515 | ||
516 | Unless you have a particular reason to use the two argument form you | |
517 | should use the three argument form of open() which does not treat any | |
518 | charcters in the filename as special. | |
519 | ||
520 | open FILE, "<", " file "; # filename is " file " | |
521 | open FILE, ">", ">file"; # filename is ">file" | |
522 | ||
523 | =head2 How can I reliably rename a file? | |
524 | X<rename> X<mv> X<move> X<file, rename> X<ren> | |
525 | ||
526 | If your operating system supports a proper mv(1) utility or its | |
527 | functional equivalent, this works: | |
528 | ||
529 | rename($old, $new) or system("mv", $old, $new); | |
530 | ||
531 | It may be more portable to use the File::Copy module instead. | |
532 | You just copy to the new file to the new name (checking return | |
533 | values), then delete the old one. This isn't really the same | |
534 | semantically as a rename(), which preserves meta-information like | |
535 | permissions, timestamps, inode info, etc. | |
536 | ||
537 | Newer versions of File::Copy export a move() function. | |
538 | ||
539 | =head2 How can I lock a file? | |
540 | X<lock> X<file, lock> X<flock> | |
541 | ||
542 | Perl's builtin flock() function (see L<perlfunc> for details) will call | |
543 | flock(2) if that exists, fcntl(2) if it doesn't (on perl version 5.004 and | |
544 | later), and lockf(3) if neither of the two previous system calls exists. | |
545 | On some systems, it may even use a different form of native locking. | |
546 | Here are some gotchas with Perl's flock(): | |
547 | ||
548 | =over 4 | |
549 | ||
550 | =item 1 | |
551 | ||
552 | Produces a fatal error if none of the three system calls (or their | |
553 | close equivalent) exists. | |
554 | ||
555 | =item 2 | |
556 | ||
557 | lockf(3) does not provide shared locking, and requires that the | |
558 | filehandle be open for writing (or appending, or read/writing). | |
559 | ||
560 | =item 3 | |
561 | ||
562 | Some versions of flock() can't lock files over a network (e.g. on NFS file | |
563 | systems), so you'd need to force the use of fcntl(2) when you build Perl. | |
564 | But even this is dubious at best. See the flock entry of L<perlfunc> | |
565 | and the F<INSTALL> file in the source distribution for information on | |
566 | building Perl to do this. | |
567 | ||
568 | Two potentially non-obvious but traditional flock semantics are that | |
569 | it waits indefinitely until the lock is granted, and that its locks are | |
570 | I<merely advisory>. Such discretionary locks are more flexible, but | |
571 | offer fewer guarantees. This means that files locked with flock() may | |
572 | be modified by programs that do not also use flock(). Cars that stop | |
573 | for red lights get on well with each other, but not with cars that don't | |
574 | stop for red lights. See the perlport manpage, your port's specific | |
575 | documentation, or your system-specific local manpages for details. It's | |
576 | best to assume traditional behavior if you're writing portable programs. | |
577 | (If you're not, you should as always feel perfectly free to write | |
578 | for your own system's idiosyncrasies (sometimes called "features"). | |
579 | Slavish adherence to portability concerns shouldn't get in the way of | |
580 | your getting your job done.) | |
581 | ||
582 | For more information on file locking, see also | |
583 | L<perlopentut/"File Locking"> if you have it (new for 5.6). | |
584 | ||
585 | =back | |
586 | ||
587 | =head2 Why can't I just open(FH, "E<gt>file.lock")? | |
588 | X<lock, lockfile race condition> | |
589 | ||
590 | A common bit of code B<NOT TO USE> is this: | |
591 | ||
592 | sleep(3) while -e "file.lock"; # PLEASE DO NOT USE | |
593 | open(LCK, "> file.lock"); # THIS BROKEN CODE | |
594 | ||
595 | This is a classic race condition: you take two steps to do something | |
596 | which must be done in one. That's why computer hardware provides an | |
597 | atomic test-and-set instruction. In theory, this "ought" to work: | |
598 | ||
599 | sysopen(FH, "file.lock", O_WRONLY|O_EXCL|O_CREAT) | |
600 | or die "can't open file.lock: $!"; | |
601 | ||
602 | except that lamentably, file creation (and deletion) is not atomic | |
603 | over NFS, so this won't work (at least, not every time) over the net. | |
604 | Various schemes involving link() have been suggested, but | |
605 | these tend to involve busy-wait, which is also subdesirable. | |
606 | ||
607 | =head2 I still don't get locking. I just want to increment the number in the file. How can I do this? | |
608 | X<counter> X<file, counter> | |
609 | ||
610 | Didn't anyone ever tell you web-page hit counters were useless? | |
611 | They don't count number of hits, they're a waste of time, and they serve | |
612 | only to stroke the writer's vanity. It's better to pick a random number; | |
613 | they're more realistic. | |
614 | ||
615 | Anyway, this is what you can do if you can't help yourself. | |
616 | ||
617 | use Fcntl qw(:DEFAULT :flock); | |
618 | sysopen(FH, "numfile", O_RDWR|O_CREAT) or die "can't open numfile: $!"; | |
619 | flock(FH, LOCK_EX) or die "can't flock numfile: $!"; | |
620 | $num = <FH> || 0; | |
621 | seek(FH, 0, 0) or die "can't rewind numfile: $!"; | |
622 | truncate(FH, 0) or die "can't truncate numfile: $!"; | |
623 | (print FH $num+1, "\n") or die "can't write numfile: $!"; | |
624 | close FH or die "can't close numfile: $!"; | |
625 | ||
626 | Here's a much better web-page hit counter: | |
627 | ||
628 | $hits = int( (time() - 850_000_000) / rand(1_000) ); | |
629 | ||
630 | If the count doesn't impress your friends, then the code might. :-) | |
631 | ||
632 | =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? | |
633 | X<append> X<file, append> | |
634 | ||
635 | If you are on a system that correctly implements flock() and you use the | |
636 | example appending code from "perldoc -f flock" everything will be OK | |
637 | even if the OS you are on doesn't implement append mode correctly (if | |
638 | such a system exists.) So if you are happy to restrict yourself to OSs | |
639 | that implement flock() (and that's not really much of a restriction) | |
640 | then that is what you should do. | |
641 | ||
642 | If you know you are only going to use a system that does correctly | |
643 | implement appending (i.e. not Win32) then you can omit the seek() from | |
644 | the above code. | |
645 | ||
646 | If you know you are only writing code to run on an OS and filesystem that | |
647 | does implement append mode correctly (a local filesystem on a modern | |
648 | Unix for example), and you keep the file in block-buffered mode and you | |
649 | write less than one buffer-full of output between each manual flushing | |
650 | of the buffer then each bufferload is almost guaranteed to be written to | |
651 | the end of the file in one chunk without getting intermingled with | |
652 | anyone else's output. You can also use the syswrite() function which is | |
653 | simply a wrapper around your systems write(2) system call. | |
654 | ||
655 | There is still a small theoretical chance that a signal will interrupt | |
656 | the system level write() operation before completion. There is also a | |
657 | possibility that some STDIO implementations may call multiple system | |
658 | level write()s even if the buffer was empty to start. There may be some | |
659 | systems where this probability is reduced to zero. | |
660 | ||
661 | =head2 How do I randomly update a binary file? | |
662 | X<file, binary patch> | |
663 | ||
664 | If you're just trying to patch a binary, in many cases something as | |
665 | simple as this works: | |
666 | ||
667 | perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs | |
668 | ||
669 | However, if you have fixed sized records, then you might do something more | |
670 | like this: | |
671 | ||
672 | $RECSIZE = 220; # size of record, in bytes | |
673 | $recno = 37; # which record to update | |
674 | open(FH, "+<somewhere") || die "can't update somewhere: $!"; | |
675 | seek(FH, $recno * $RECSIZE, 0); | |
676 | read(FH, $record, $RECSIZE) == $RECSIZE || die "can't read record $recno: $!"; | |
677 | # munge the record | |
678 | seek(FH, -$RECSIZE, 1); | |
679 | print FH $record; | |
680 | close FH; | |
681 | ||
682 | Locking and error checking are left as an exercise for the reader. | |
683 | Don't forget them or you'll be quite sorry. | |
684 | ||
685 | =head2 How do I get a file's timestamp in perl? | |
686 | X<timestamp> X<file, timestamp> | |
687 | ||
688 | If you want to retrieve the time at which the file was last | |
689 | read, written, or had its meta-data (owner, etc) changed, | |
690 | you use the B<-A>, B<-M>, or B<-C> file test operations as | |
691 | documented in L<perlfunc>. These retrieve the age of the | |
692 | file (measured against the start-time of your program) in | |
693 | days as a floating point number. Some platforms may not have | |
694 | all of these times. See L<perlport> for details. To | |
695 | retrieve the "raw" time in seconds since the epoch, you | |
696 | would call the stat function, then use localtime(), | |
697 | gmtime(), or POSIX::strftime() to convert this into | |
698 | human-readable form. | |
699 | ||
700 | Here's an example: | |
701 | ||
702 | $write_secs = (stat($file))[9]; | |
703 | printf "file %s updated at %s\n", $file, | |
704 | scalar localtime($write_secs); | |
705 | ||
706 | If you prefer something more legible, use the File::stat module | |
707 | (part of the standard distribution in version 5.004 and later): | |
708 | ||
709 | # error checking left as an exercise for reader. | |
710 | use File::stat; | |
711 | use Time::localtime; | |
712 | $date_string = ctime(stat($file)->mtime); | |
713 | print "file $file updated at $date_string\n"; | |
714 | ||
715 | The POSIX::strftime() approach has the benefit of being, | |
716 | in theory, independent of the current locale. See L<perllocale> | |
717 | for details. | |
718 | ||
719 | =head2 How do I set a file's timestamp in perl? | |
720 | X<timestamp> X<file, timestamp> | |
721 | ||
722 | You use the utime() function documented in L<perlfunc/utime>. | |
723 | By way of example, here's a little program that copies the | |
724 | read and write times from its first argument to all the rest | |
725 | of them. | |
726 | ||
727 | if (@ARGV < 2) { | |
728 | die "usage: cptimes timestamp_file other_files ...\n"; | |
729 | } | |
730 | $timestamp = shift; | |
731 | ($atime, $mtime) = (stat($timestamp))[8,9]; | |
732 | utime $atime, $mtime, @ARGV; | |
733 | ||
734 | Error checking is, as usual, left as an exercise for the reader. | |
735 | ||
736 | The perldoc for utime also has an example that has the same | |
737 | effect as touch(1) on files that I<already exist>. | |
738 | ||
739 | Certain file systems have a limited ability to store the times | |
740 | on a file at the expected level of precision. For example, the | |
741 | FAT and HPFS filesystem are unable to create dates on files with | |
742 | a finer granularity than two seconds. This is a limitation of | |
743 | the filesystems, not of utime(). | |
744 | ||
745 | =head2 How do I print to more than one file at once? | |
746 | X<print, to multiple files> | |
747 | ||
748 | To connect one filehandle to several output filehandles, | |
749 | you can use the IO::Tee or Tie::FileHandle::Multiplex modules. | |
750 | ||
751 | If you only have to do this once, you can print individually | |
752 | to each filehandle. | |
753 | ||
754 | for $fh (FH1, FH2, FH3) { print $fh "whatever\n" } | |
755 | ||
756 | =head2 How can I read in an entire file all at once? | |
757 | X<slurp> X<file, slurping> | |
758 | ||
759 | You can use the File::Slurp module to do it in one step. | |
760 | ||
761 | use File::Slurp; | |
762 | ||
763 | $all_of_it = read_file($filename); # entire file in scalar | |
764 | @all_lines = read_file($filename); # one line perl element | |
765 | ||
766 | The customary Perl approach for processing all the lines in a file is to | |
767 | do so one line at a time: | |
768 | ||
769 | open (INPUT, $file) || die "can't open $file: $!"; | |
770 | while (<INPUT>) { | |
771 | chomp; | |
772 | # do something with $_ | |
773 | } | |
774 | close(INPUT) || die "can't close $file: $!"; | |
775 | ||
776 | This is tremendously more efficient than reading the entire file into | |
777 | memory as an array of lines and then processing it one element at a time, | |
778 | which is often--if not almost always--the wrong approach. Whenever | |
779 | you see someone do this: | |
780 | ||
781 | @lines = <INPUT>; | |
782 | ||
783 | you should think long and hard about why you need everything loaded at | |
784 | once. It's just not a scalable solution. You might also find it more | |
785 | fun to use the standard Tie::File module, or the DB_File module's | |
786 | $DB_RECNO bindings, which allow you to tie an array to a file so that | |
787 | accessing an element the array actually accesses the corresponding | |
788 | line in the file. | |
789 | ||
790 | You can read the entire filehandle contents into a scalar. | |
791 | ||
792 | { | |
793 | local(*INPUT, $/); | |
794 | open (INPUT, $file) || die "can't open $file: $!"; | |
795 | $var = <INPUT>; | |
796 | } | |
797 | ||
798 | That temporarily undefs your record separator, and will automatically | |
799 | close the file at block exit. If the file is already open, just use this: | |
800 | ||
801 | $var = do { local $/; <INPUT> }; | |
802 | ||
803 | For ordinary files you can also use the read function. | |
804 | ||
805 | read( INPUT, $var, -s INPUT ); | |
806 | ||
807 | The third argument tests the byte size of the data on the INPUT filehandle | |
808 | and reads that many bytes into the buffer $var. | |
809 | ||
810 | =head2 How can I read in a file by paragraphs? | |
811 | X<file, reading by paragraphs> | |
812 | ||
813 | Use the C<$/> variable (see L<perlvar> for details). You can either | |
814 | set it to C<""> to eliminate empty paragraphs (C<"abc\n\n\n\ndef">, | |
815 | for instance, gets treated as two paragraphs and not three), or | |
816 | C<"\n\n"> to accept empty paragraphs. | |
817 | ||
818 | Note that a blank line must have no blanks in it. Thus | |
819 | S<C<"fred\n \nstuff\n\n">> is one paragraph, but C<"fred\n\nstuff\n\n"> is two. | |
820 | ||
821 | =head2 How can I read a single character from a file? From the keyboard? | |
822 | X<getc> X<file, reading one character at a time> | |
823 | ||
824 | You can use the builtin C<getc()> function for most filehandles, but | |
825 | it won't (easily) work on a terminal device. For STDIN, either use | |
826 | the Term::ReadKey module from CPAN or use the sample code in | |
827 | L<perlfunc/getc>. | |
828 | ||
829 | If your system supports the portable operating system programming | |
830 | interface (POSIX), you can use the following code, which you'll note | |
831 | turns off echo processing as well. | |
832 | ||
833 | #!/usr/bin/perl -w | |
834 | use strict; | |
835 | $| = 1; | |
836 | for (1..4) { | |
837 | my $got; | |
838 | print "gimme: "; | |
839 | $got = getone(); | |
840 | print "--> $got\n"; | |
841 | } | |
842 | exit; | |
843 | ||
844 | BEGIN { | |
845 | use POSIX qw(:termios_h); | |
846 | ||
847 | my ($term, $oterm, $echo, $noecho, $fd_stdin); | |
848 | ||
849 | $fd_stdin = fileno(STDIN); | |
850 | ||
851 | $term = POSIX::Termios->new(); | |
852 | $term->getattr($fd_stdin); | |
853 | $oterm = $term->getlflag(); | |
854 | ||
855 | $echo = ECHO | ECHOK | ICANON; | |
856 | $noecho = $oterm & ~$echo; | |
857 | ||
858 | sub cbreak { | |
859 | $term->setlflag($noecho); | |
860 | $term->setcc(VTIME, 1); | |
861 | $term->setattr($fd_stdin, TCSANOW); | |
862 | } | |
863 | ||
864 | sub cooked { | |
865 | $term->setlflag($oterm); | |
866 | $term->setcc(VTIME, 0); | |
867 | $term->setattr($fd_stdin, TCSANOW); | |
868 | } | |
869 | ||
870 | sub getone { | |
871 | my $key = ''; | |
872 | cbreak(); | |
873 | sysread(STDIN, $key, 1); | |
874 | cooked(); | |
875 | return $key; | |
876 | } | |
877 | ||
878 | } | |
879 | ||
880 | END { cooked() } | |
881 | ||
882 | The Term::ReadKey module from CPAN may be easier to use. Recent versions | |
883 | include also support for non-portable systems as well. | |
884 | ||
885 | use Term::ReadKey; | |
886 | open(TTY, "</dev/tty"); | |
887 | print "Gimme a char: "; | |
888 | ReadMode "raw"; | |
889 | $key = ReadKey 0, *TTY; | |
890 | ReadMode "normal"; | |
891 | printf "\nYou said %s, char number %03d\n", | |
892 | $key, ord $key; | |
893 | ||
894 | =head2 How can I tell whether there's a character waiting on a filehandle? | |
895 | ||
896 | The very first thing you should do is look into getting the Term::ReadKey | |
897 | extension from CPAN. As we mentioned earlier, it now even has limited | |
898 | support for non-portable (read: not open systems, closed, proprietary, | |
899 | not POSIX, not Unix, etc) systems. | |
900 | ||
901 | You should also check out the Frequently Asked Questions list in | |
902 | comp.unix.* for things like this: the answer is essentially the same. | |
903 | It's very system dependent. Here's one solution that works on BSD | |
904 | systems: | |
905 | ||
906 | sub key_ready { | |
907 | my($rin, $nfd); | |
908 | vec($rin, fileno(STDIN), 1) = 1; | |
909 | return $nfd = select($rin,undef,undef,0); | |
910 | } | |
911 | ||
912 | If you want to find out how many characters are waiting, there's | |
913 | also the FIONREAD ioctl call to be looked at. The I<h2ph> tool that | |
914 | comes with Perl tries to convert C include files to Perl code, which | |
915 | can be C<require>d. FIONREAD ends up defined as a function in the | |
916 | I<sys/ioctl.ph> file: | |
917 | ||
918 | require 'sys/ioctl.ph'; | |
919 | ||
920 | $size = pack("L", 0); | |
921 | ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n"; | |
922 | $size = unpack("L", $size); | |
923 | ||
924 | If I<h2ph> wasn't installed or doesn't work for you, you can | |
925 | I<grep> the include files by hand: | |
926 | ||
927 | % grep FIONREAD /usr/include/*/* | |
928 | /usr/include/asm/ioctls.h:#define FIONREAD 0x541B | |
929 | ||
930 | Or write a small C program using the editor of champions: | |
931 | ||
932 | % cat > fionread.c | |
933 | #include <sys/ioctl.h> | |
934 | main() { | |
935 | printf("%#08x\n", FIONREAD); | |
936 | } | |
937 | ^D | |
938 | % cc -o fionread fionread.c | |
939 | % ./fionread | |
940 | 0x4004667f | |
941 | ||
942 | And then hard code it, leaving porting as an exercise to your successor. | |
943 | ||
944 | $FIONREAD = 0x4004667f; # XXX: opsys dependent | |
945 | ||
946 | $size = pack("L", 0); | |
947 | ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n"; | |
948 | $size = unpack("L", $size); | |
949 | ||
950 | FIONREAD requires a filehandle connected to a stream, meaning that sockets, | |
951 | pipes, and tty devices work, but I<not> files. | |
952 | ||
953 | =head2 How do I do a C<tail -f> in perl? | |
954 | X<tail> | |
955 | ||
956 | First try | |
957 | ||
958 | seek(GWFILE, 0, 1); | |
959 | ||
960 | The statement C<seek(GWFILE, 0, 1)> doesn't change the current position, | |
961 | but it does clear the end-of-file condition on the handle, so that the | |
962 | next <GWFILE> makes Perl try again to read something. | |
963 | ||
964 | If that doesn't work (it relies on features of your stdio implementation), | |
965 | then you need something more like this: | |
966 | ||
967 | for (;;) { | |
968 | for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE)) { | |
969 | # search for some stuff and put it into files | |
970 | } | |
971 | # sleep for a while | |
972 | seek(GWFILE, $curpos, 0); # seek to where we had been | |
973 | } | |
974 | ||
975 | If this still doesn't work, look into the POSIX module. POSIX defines | |
976 | the clearerr() method, which can remove the end of file condition on a | |
977 | filehandle. The method: read until end of file, clearerr(), read some | |
978 | more. Lather, rinse, repeat. | |
979 | ||
980 | There's also a File::Tail module from CPAN. | |
981 | ||
982 | =head2 How do I dup() a filehandle in Perl? | |
983 | X<dup> | |
984 | ||
985 | If you check L<perlfunc/open>, you'll see that several of the ways | |
986 | to call open() should do the trick. For example: | |
987 | ||
988 | open(LOG, ">>/foo/logfile"); | |
989 | open(STDERR, ">&LOG"); | |
990 | ||
991 | Or even with a literal numeric descriptor: | |
992 | ||
993 | $fd = $ENV{MHCONTEXTFD}; | |
994 | open(MHCONTEXT, "<&=$fd"); # like fdopen(3S) | |
995 | ||
996 | Note that "<&STDIN" makes a copy, but "<&=STDIN" make | |
997 | an alias. That means if you close an aliased handle, all | |
998 | aliases become inaccessible. This is not true with | |
999 | a copied one. | |
1000 | ||
1001 | Error checking, as always, has been left as an exercise for the reader. | |
1002 | ||
1003 | =head2 How do I close a file descriptor by number? | |
1004 | X<file, closing file descriptors> | |
1005 | ||
1006 | This should rarely be necessary, as the Perl close() function is to be | |
1007 | used for things that Perl opened itself, even if it was a dup of a | |
1008 | numeric descriptor as with MHCONTEXT above. But if you really have | |
1009 | to, you may be able to do this: | |
1010 | ||
1011 | require 'sys/syscall.ph'; | |
1012 | $rc = syscall(&SYS_close, $fd + 0); # must force numeric | |
1013 | die "can't sysclose $fd: $!" unless $rc == -1; | |
1014 | ||
1015 | Or, just use the fdopen(3S) feature of open(): | |
1016 | ||
1017 | { | |
1018 | local *F; | |
1019 | open F, "<&=$fd" or die "Cannot reopen fd=$fd: $!"; | |
1020 | close F; | |
1021 | } | |
1022 | ||
1023 | =head2 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work? | |
1024 | X<filename, DOS issues> | |
1025 | ||
1026 | Whoops! You just put a tab and a formfeed into that filename! | |
1027 | Remember that within double quoted strings ("like\this"), the | |
1028 | backslash is an escape character. The full list of these is in | |
1029 | L<perlop/Quote and Quote-like Operators>. Unsurprisingly, you don't | |
1030 | have a file called "c:(tab)emp(formfeed)oo" or | |
1031 | "c:(tab)emp(formfeed)oo.exe" on your legacy DOS filesystem. | |
1032 | ||
1033 | Either single-quote your strings, or (preferably) use forward slashes. | |
1034 | Since all DOS and Windows versions since something like MS-DOS 2.0 or so | |
1035 | have treated C</> and C<\> the same in a path, you might as well use the | |
1036 | one that doesn't clash with Perl--or the POSIX shell, ANSI C and C++, | |
1037 | awk, Tcl, Java, or Python, just to mention a few. POSIX paths | |
1038 | are more portable, too. | |
1039 | ||
1040 | =head2 Why doesn't glob("*.*") get all the files? | |
1041 | X<glob> | |
1042 | ||
1043 | Because even on non-Unix ports, Perl's glob function follows standard | |
1044 | Unix globbing semantics. You'll need C<glob("*")> to get all (non-hidden) | |
1045 | files. This makes glob() portable even to legacy systems. Your | |
1046 | port may include proprietary globbing functions as well. Check its | |
1047 | documentation for details. | |
1048 | ||
1049 | =head2 Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl? | |
1050 | ||
1051 | This is elaborately and painstakingly described in the | |
1052 | F<file-dir-perms> article in the "Far More Than You Ever Wanted To | |
1053 | Know" collection in http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz . | |
1054 | ||
1055 | The executive summary: learn how your filesystem works. The | |
1056 | permissions on a file say what can happen to the data in that file. | |
1057 | The permissions on a directory say what can happen to the list of | |
1058 | files in that directory. If you delete a file, you're removing its | |
1059 | name from the directory (so the operation depends on the permissions | |
1060 | of the directory, not of the file). If you try to write to the file, | |
1061 | the permissions of the file govern whether you're allowed to. | |
1062 | ||
1063 | =head2 How do I select a random line from a file? | |
1064 | X<file, selecting a random line> | |
1065 | ||
1066 | Here's an algorithm from the Camel Book: | |
1067 | ||
1068 | srand; | |
1069 | rand($.) < 1 && ($line = $_) while <>; | |
1070 | ||
1071 | This has a significant advantage in space over reading the whole file | |
1072 | in. You can find a proof of this method in I<The Art of Computer | |
1073 | Programming>, Volume 2, Section 3.4.2, by Donald E. Knuth. | |
1074 | ||
1075 | You can use the File::Random module which provides a function | |
1076 | for that algorithm: | |
1077 | ||
1078 | use File::Random qw/random_line/; | |
1079 | my $line = random_line($filename); | |
1080 | ||
1081 | Another way is to use the Tie::File module, which treats the entire | |
1082 | file as an array. Simply access a random array element. | |
1083 | ||
1084 | =head2 Why do I get weird spaces when I print an array of lines? | |
1085 | ||
1086 | Saying | |
1087 | ||
1088 | print "@lines\n"; | |
1089 | ||
1090 | joins together the elements of C<@lines> with a space between them. | |
1091 | If C<@lines> were C<("little", "fluffy", "clouds")> then the above | |
1092 | statement would print | |
1093 | ||
1094 | little fluffy clouds | |
1095 | ||
1096 | but if each element of C<@lines> was a line of text, ending a newline | |
1097 | character C<("little\n", "fluffy\n", "clouds\n")> then it would print: | |
1098 | ||
1099 | little | |
1100 | fluffy | |
1101 | clouds | |
1102 | ||
1103 | If your array contains lines, just print them: | |
1104 | ||
1105 | print @lines; | |
1106 | ||
1107 | =head1 AUTHOR AND COPYRIGHT | |
1108 | ||
1109 | Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and | |
1110 | other authors as noted. All rights reserved. | |
1111 | ||
1112 | This documentation is free; you can redistribute it and/or modify it | |
1113 | under the same terms as Perl itself. | |
1114 | ||
1115 | Irrespective of its distribution, all code examples here are in the public | |
1116 | domain. You are permitted and encouraged to use this code and any | |
1117 | derivatives thereof in your own programs for fun or for profit as you | |
1118 | see fit. A simple comment in the code giving credit to the FAQ would | |
1119 | be courteous but is not required. |