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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "PERLINTRO 1" | |
132 | .TH PERLINTRO 1 "2002-06-08" "perl v5.8.0" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | perlintro \-\- a brief introduction and overview of Perl | |
135 | .SH "DESCRIPTION" | |
136 | .IX Header "DESCRIPTION" | |
137 | This document is intended to give you a quick overview of the Perl | |
138 | programming language, along with pointers to further documentation. It | |
139 | is intended as a \*(L"bootstrap\*(R" guide for those who are new to the | |
140 | language, and provides just enough information for you to be able to | |
141 | read other peoples' Perl and understand roughly what it's doing, or | |
142 | write your own simple scripts. | |
143 | .PP | |
144 | This introductory document does not aim to be complete. It does not | |
145 | even aim to be entirely accurate. In some cases perfection has been | |
146 | sacrificed in the goal of getting the general idea across. You are | |
147 | \&\fIstrongly\fR advised to follow this introduction with more information | |
148 | from the full Perl manual, the table of contents to which can be found | |
149 | in perltoc. | |
150 | .PP | |
151 | Throughout this document you'll see references to other parts of the | |
152 | Perl documentation. You can read that documentation using the \f(CW\*(C`perldoc\*(C'\fR | |
153 | command or whatever method you're using to read this document. | |
154 | .Sh "What is Perl?" | |
155 | .IX Subsection "What is Perl?" | |
156 | Perl is a general-purpose programming language originally developed for | |
157 | text manipulation and now used for a wide range of tasks including | |
158 | system administration, web development, network programming, \s-1GUI\s0 | |
159 | development, and more. | |
160 | .PP | |
161 | The language is intended to be practical (easy to use, efficient, | |
162 | complete) rather than beautiful (tiny, elegant, minimal). Its major | |
163 | features are that it's easy to use, supports both procedural and | |
164 | object-oriented (\s-1OO\s0) programming, has powerful built-in support for text | |
165 | processing, and has one of the world's most impressive collections of | |
166 | third-party modules. | |
167 | .PP | |
168 | Different definitions of Perl are given in perl, perlfaq1 and | |
169 | no doubt other places. From this we can determine that Perl is different | |
170 | things to different people, but that lots of people think it's at least | |
171 | worth writing about. | |
172 | .Sh "Running Perl programs" | |
173 | .IX Subsection "Running Perl programs" | |
174 | To run a Perl program from the Unix command line: | |
175 | .PP | |
176 | .Vb 1 | |
177 | \& perl progname.pl | |
178 | .Ve | |
179 | .PP | |
180 | Alternatively, put this as the first line of your script: | |
181 | .PP | |
182 | .Vb 1 | |
183 | \& #!/usr/bin/env perl | |
184 | .Ve | |
185 | .PP | |
186 | \&... and run the script as \f(CW\*(C`/path/to/script.pl\*(C'\fR. Of course, it'll need | |
187 | to be executable first, so \f(CW\*(C`chmod 755 script.pl\*(C'\fR (under Unix). | |
188 | .PP | |
189 | For more information, including instructions for other platforms such as | |
190 | Windows and Mac \s-1OS\s0, read perlrun. | |
191 | .Sh "Basic syntax overview" | |
192 | .IX Subsection "Basic syntax overview" | |
193 | A Perl script or program consists of one or more statements. These | |
194 | statements are simply written in the script in a straightforward | |
195 | fashion. There is no need to have a \f(CW\*(C`main()\*(C'\fR function or anything of | |
196 | that kind. | |
197 | .PP | |
198 | Perl statements end in a semi\-colon: | |
199 | .PP | |
200 | .Vb 1 | |
201 | \& print "Hello, world"; | |
202 | .Ve | |
203 | .PP | |
204 | Comments start with a hash symbol and run to the end of the line | |
205 | .PP | |
206 | .Vb 1 | |
207 | \& # This is a comment | |
208 | .Ve | |
209 | .PP | |
210 | Whitespace is irrelevant: | |
211 | .PP | |
212 | .Vb 3 | |
213 | ||
214 | \& "Hello, world" | |
215 | \& ; | |
216 | .Ve | |
217 | .PP | |
218 | \&... except inside quoted strings: | |
219 | .PP | |
220 | .Vb 3 | |
221 | \& # this would print with a linebreak in the middle | |
222 | \& print "Hello | |
223 | \& world"; | |
224 | .Ve | |
225 | .PP | |
226 | Double quotes or single quotes may be used around literal strings: | |
227 | .PP | |
228 | .Vb 2 | |
229 | \& print "Hello, world"; | |
230 | \& print 'Hello, world'; | |
231 | .Ve | |
232 | .PP | |
233 | However, only double quotes \*(L"interpolate\*(R" variables and special | |
234 | characters such as newlines (\f(CW\*(C`\en\*(C'\fR): | |
235 | .PP | |
236 | .Vb 2 | |
237 | \& print "Hello, $name\en"; # works fine | |
238 | \& print 'Hello, $name\en'; # prints $name\en literally | |
239 | .Ve | |
240 | .PP | |
241 | Numbers don't need quotes around them: | |
242 | .PP | |
243 | .Vb 1 | |
244 | \& print 42; | |
245 | .Ve | |
246 | .PP | |
247 | You can use parentheses for functions' arguments or omit them | |
248 | according to your personal taste. They are only required | |
249 | occasionally to clarify issues of precedence. | |
250 | .PP | |
251 | .Vb 2 | |
252 | \& print("Hello, world\en"); | |
253 | \& print "Hello, world\en"; | |
254 | .Ve | |
255 | .PP | |
256 | More detailed information about Perl syntax can be found in perlsyn. | |
257 | .Sh "Perl variable types" | |
258 | .IX Subsection "Perl variable types" | |
259 | Perl has three main variable types: scalars, arrays, and hashes. | |
260 | .IP "Scalars" 4 | |
261 | .IX Item "Scalars" | |
262 | A scalar represents a single value: | |
263 | .Sp | |
264 | .Vb 2 | |
265 | \& my $animal = "camel"; | |
266 | \& my $answer = 42; | |
267 | .Ve | |
268 | .Sp | |
269 | Scalar values can be strings, integers or floating point numbers, and Perl | |
270 | will automatically convert between them as required. There is no need | |
271 | to pre-declare your variable types. | |
272 | .Sp | |
273 | Scalar values can be used in various ways: | |
274 | .Sp | |
275 | .Vb 3 | |
276 | \& print $animal; | |
277 | \& print "The animal is $animal\en"; | |
278 | \& print "The square of $answer is ", $answer * $answer, "\en"; | |
279 | .Ve | |
280 | .Sp | |
281 | There are a number of \*(L"magic\*(R" scalars with names that look like | |
282 | punctuation or line noise. These special variables are used for all | |
283 | kinds of purposes, and are documented in perlvar. The only one you | |
284 | need to know about for now is \f(CW$_\fR which is the \*(L"default variable\*(R". | |
285 | It's used as the default argument to a number of functions in Perl, and | |
286 | it's set implicitly by certain looping constructs. | |
287 | .Sp | |
288 | .Vb 1 | |
289 | \& print; # prints contents of $_ by default | |
290 | .Ve | |
291 | .IP "Arrays" 4 | |
292 | .IX Item "Arrays" | |
293 | An array represents a list of values: | |
294 | .Sp | |
295 | .Vb 3 | |
296 | \& my @animals = ("camel", "llama", "owl"); | |
297 | \& my @numbers = (23, 42, 69); | |
298 | \& my @mixed = ("camel", 42, 1.23); | |
299 | .Ve | |
300 | .Sp | |
301 | Arrays are zero\-indexed. Here's how you get at elements in an array: | |
302 | .Sp | |
303 | .Vb 2 | |
304 | \& print $animals[0]; # prints "camel" | |
305 | \& print $animals[1]; # prints "llama" | |
306 | .Ve | |
307 | .Sp | |
308 | The special variable \f(CW$#array\fR tells you the index of the last element | |
309 | of an array: | |
310 | .Sp | |
311 | .Vb 1 | |
312 | \& print $mixed[$#mixed]; # last element, prints 1.23 | |
313 | .Ve | |
314 | .Sp | |
315 | You might be tempted to use \f(CW\*(C`$#array + 1\*(C'\fR to tell you how many items there | |
316 | are in an array. Don't bother. As it happens, using \f(CW@array\fR where Perl | |
317 | expects to find a scalar value (\*(L"in scalar context\*(R") will give you the number | |
318 | of elements in the array: | |
319 | .Sp | |
320 | .Vb 1 | |
321 | \& if (@animals < 5) { ... } | |
322 | .Ve | |
323 | .Sp | |
324 | The elements we're getting from the array start with a \f(CW\*(C`$\*(C'\fR because | |
325 | we're getting just a single value out of the array \*(-- you ask for a scalar, | |
326 | you get a scalar. | |
327 | .Sp | |
328 | To get multiple values from an array: | |
329 | .Sp | |
330 | .Vb 3 | |
331 | \& @animals[0,1]; # gives ("camel", "llama"); | |
332 | \& @animals[0..2]; # gives ("camel", "llama", "owl"); | |
333 | \& @animals[1..$#animals]; # gives all except the first element | |
334 | .Ve | |
335 | .Sp | |
336 | This is called an \*(L"array slice\*(R". | |
337 | .Sp | |
338 | You can do various useful things to lists: | |
339 | .Sp | |
340 | .Vb 2 | |
341 | \& my @sorted = sort @animals; | |
342 | \& my @backwards = reverse @numbers; | |
343 | .Ve | |
344 | .Sp | |
345 | There are a couple of special arrays too, such as \f(CW@ARGV\fR (the command | |
346 | line arguments to your script) and \f(CW@_\fR (the arguments passed to a | |
347 | subroutine). These are documented in perlvar. | |
348 | .IP "Hashes" 4 | |
349 | .IX Item "Hashes" | |
350 | A hash represents a set of key/value pairs: | |
351 | .Sp | |
352 | .Vb 1 | |
353 | \& my %fruit_color = ("apple", "red", "banana", "yellow"); | |
354 | .Ve | |
355 | .Sp | |
356 | You can use whitespace and the \f(CW\*(C`=>\*(C'\fR operator to lay them out more | |
357 | nicely: | |
358 | .Sp | |
359 | .Vb 4 | |
360 | \& my %fruit_color = ( | |
361 | \& apple => "red", | |
362 | \& banana => "yellow", | |
363 | \& ); | |
364 | .Ve | |
365 | .Sp | |
366 | To get at hash elements: | |
367 | .Sp | |
368 | .Vb 1 | |
369 | \& $fruit_color{"apple"}; # gives "red" | |
370 | .Ve | |
371 | .Sp | |
372 | You can get at lists of keys and values with \f(CW\*(C`keys()\*(C'\fR and | |
373 | \&\f(CW\*(C`values()\*(C'\fR. | |
374 | .Sp | |
375 | .Vb 2 | |
376 | \& my @fruits = keys %fruit_colors; | |
377 | \& my @colors = values %fruit_colors; | |
378 | .Ve | |
379 | .Sp | |
380 | Hashes have no particular internal order, though you can sort the keys | |
381 | and loop through them. | |
382 | .Sp | |
383 | Just like special scalars and arrays, there are also special hashes. | |
384 | The most well known of these is \f(CW%ENV\fR which contains environment | |
385 | variables. Read all about it (and other special variables) in | |
386 | perlvar. | |
387 | .PP | |
388 | Scalars, arrays and hashes are documented more fully in perldata. | |
389 | .PP | |
390 | More complex data types can be constructed using references, which allow | |
391 | you to build lists and hashes within lists and hashes. | |
392 | .PP | |
393 | A reference is a scalar value and can refer to any other Perl data | |
394 | type. So by storing a reference as the value of an array or hash | |
395 | element, you can easily create lists and hashes within lists and | |
396 | hashes. The following example shows a 2 level hash of hash | |
397 | structure using anonymous hash references. | |
398 | .PP | |
399 | .Vb 14 | |
400 | \& my $variables = { | |
401 | \& scalar => { | |
402 | \& description => "single item", | |
403 | \& sigil => '$', | |
404 | \& }, | |
405 | \& array => { | |
406 | \& description => "ordered list of items", | |
407 | \& sigil => '@', | |
408 | \& }, | |
409 | \& hash => { | |
410 | \& description => "key/value pairs", | |
411 | \& sigil => '%', | |
412 | \& }, | |
413 | \& }; | |
414 | .Ve | |
415 | .PP | |
416 | .Vb 1 | |
417 | \& print "Scalars begin with a $variables->{'scalar'}->{'sigil'}\en"; | |
418 | .Ve | |
419 | .PP | |
420 | Exhaustive information on the topic of references can be found in | |
421 | perlreftut, perllol, perlref and perldsc. | |
422 | .Sh "Variable scoping" | |
423 | .IX Subsection "Variable scoping" | |
424 | Throughout the previous section all the examples have used the syntax: | |
425 | .PP | |
426 | .Vb 1 | |
427 | \& my $var = "value"; | |
428 | .Ve | |
429 | .PP | |
430 | The \f(CW\*(C`my\*(C'\fR is actually not required; you could just use: | |
431 | .PP | |
432 | .Vb 1 | |
433 | \& $var = "value"; | |
434 | .Ve | |
435 | .PP | |
436 | However, the above usage will create global variables throughout your | |
437 | program, which is bad programming practice. \f(CW\*(C`my\*(C'\fR creates lexically | |
438 | scoped variables instead. The variables are scoped to the block | |
439 | (i.e. a bunch of statements surrounded by curly\-braces) in which they | |
440 | are defined. | |
441 | .PP | |
442 | .Vb 8 | |
443 | \& my $a = "foo"; | |
444 | \& if ($some_condition) { | |
445 | \& my $b = "bar"; | |
446 | \& print $a; # prints "foo" | |
447 | \& print $b; # prints "bar" | |
448 | \& } | |
449 | \& print $a; # prints "foo" | |
450 | \& print $b; # prints nothing; $b has fallen out of scope | |
451 | .Ve | |
452 | .PP | |
453 | Using \f(CW\*(C`my\*(C'\fR in combination with a \f(CW\*(C`use strict;\*(C'\fR at the top of | |
454 | your Perl scripts means that the interpreter will pick up certain common | |
455 | programming errors. For instance, in the example above, the final | |
456 | \&\f(CW\*(C`print $b\*(C'\fR would cause a compile-time error and prevent you from | |
457 | running the program. Using \f(CW\*(C`strict\*(C'\fR is highly recommended. | |
458 | .Sh "Conditional and looping constructs" | |
459 | .IX Subsection "Conditional and looping constructs" | |
460 | Perl has most of the usual conditional and looping constructs except for | |
461 | case/switch (but if you really want it, there is a Switch module in Perl | |
462 | 5.8 and newer, and on \s-1CPAN\s0. See the section on modules, below, for more | |
463 | information about modules and \s-1CPAN\s0). | |
464 | .PP | |
465 | The conditions can be any Perl expression. See the list of operators in | |
466 | the next section for information on comparison and boolean logic operators, | |
467 | which are commonly used in conditional statements. | |
468 | .IP "if" 4 | |
469 | .IX Item "if" | |
470 | .Vb 7 | |
471 | \& if ( condition ) { | |
472 | \& ... | |
473 | \& } elsif ( other condition ) { | |
474 | \& ... | |
475 | \& } else { | |
476 | \& ... | |
477 | \& } | |
478 | .Ve | |
479 | .Sp | |
480 | There's also a negated version of it: | |
481 | .Sp | |
482 | .Vb 3 | |
483 | \& unless ( condition ) { | |
484 | \& ... | |
485 | \& } | |
486 | .Ve | |
487 | .Sp | |
488 | This is provided as a more readable version of \f(CW\*(C`if (!\f(CIcondition\f(CW)\*(C'\fR. | |
489 | .Sp | |
490 | Note that the braces are required in Perl, even if you've only got one | |
491 | line in the block. However, there is a clever way of making your one-line | |
492 | conditional blocks more English like: | |
493 | .Sp | |
494 | .Vb 4 | |
495 | \& # the traditional way | |
496 | \& if ($zippy) { | |
497 | \& print "Yow!"; | |
498 | \& } | |
499 | .Ve | |
500 | .Sp | |
501 | .Vb 3 | |
502 | \& # the Perlish post-condition way | |
503 | \& print "Yow!" if $zippy; | |
504 | \& print "We have no bananas" unless $bananas; | |
505 | .Ve | |
506 | .IP "while" 4 | |
507 | .IX Item "while" | |
508 | .Vb 3 | |
509 | \& while ( condition ) { | |
510 | \& ... | |
511 | \& } | |
512 | .Ve | |
513 | .Sp | |
514 | There's also a negated version, for the same reason we have \f(CW\*(C`unless\*(C'\fR: | |
515 | .Sp | |
516 | .Vb 3 | |
517 | \& until ( condition ) { | |
518 | \& ... | |
519 | \& } | |
520 | .Ve | |
521 | .Sp | |
522 | You can also use \f(CW\*(C`while\*(C'\fR in a post\-condition: | |
523 | .Sp | |
524 | .Vb 1 | |
525 | \& print "LA LA LA\en" while 1; # loops forever | |
526 | .Ve | |
527 | .IP "for" 4 | |
528 | .IX Item "for" | |
529 | Exactly like C: | |
530 | .Sp | |
531 | .Vb 3 | |
532 | \& for ($i=0; $i <= $max; $i++) { | |
533 | \& ... | |
534 | \& } | |
535 | .Ve | |
536 | .Sp | |
537 | The C style for loop is rarely needed in Perl since Perl provides | |
538 | the more friendly list scanning \f(CW\*(C`foreach\*(C'\fR loop. | |
539 | .IP "foreach" 4 | |
540 | .IX Item "foreach" | |
541 | .Vb 3 | |
542 | \& foreach (@array) { | |
543 | \& print "This element is $_\en"; | |
544 | \& } | |
545 | .Ve | |
546 | .Sp | |
547 | .Vb 4 | |
548 | \& # you don't have to use the default $_ either... | |
549 | \& foreach my $key (keys %hash) { | |
550 | \& print "The value of $key is $hash{$key}\en"; | |
551 | \& } | |
552 | .Ve | |
553 | .PP | |
554 | For more detail on looping constructs (and some that weren't mentioned in | |
555 | this overview) see perlsyn. | |
556 | .Sh "Builtin operators and functions" | |
557 | .IX Subsection "Builtin operators and functions" | |
558 | Perl comes with a wide selection of builtin functions. Some of the ones | |
559 | we've already seen include \f(CW\*(C`print\*(C'\fR, \f(CW\*(C`sort\*(C'\fR and \f(CW\*(C`reverse\*(C'\fR. A list of | |
560 | them is given at the start of perlfunc and you can easily read | |
561 | about any given function by using \f(CW\*(C`perldoc \-f \f(CIfunctionname\f(CW\*(C'\fR. | |
562 | .PP | |
563 | Perl operators are documented in full in perlop, but here are a few | |
564 | of the most common ones: | |
565 | .IP "Arithmetic" 4 | |
566 | .IX Item "Arithmetic" | |
567 | .Vb 4 | |
568 | \& + addition | |
569 | \& - subtraction | |
570 | \& * multiplication | |
571 | \& / division | |
572 | .Ve | |
573 | .IP "Numeric comparison" 4 | |
574 | .IX Item "Numeric comparison" | |
575 | .Vb 6 | |
576 | \& == equality | |
577 | \& != inequality | |
578 | \& < less than | |
579 | \& > greater than | |
580 | \& <= less than or equal | |
581 | \& >= greater than or equal | |
582 | .Ve | |
583 | .IP "String comparison" 4 | |
584 | .IX Item "String comparison" | |
585 | .Vb 6 | |
586 | \& eq equality | |
587 | \& ne inequality | |
588 | \& lt less than | |
589 | \& gt greater than | |
590 | \& le less than or equal | |
591 | \& ge greater than or equal | |
592 | .Ve | |
593 | .Sp | |
594 | (Why do we have separate numeric and string comparisons? Because we don't | |
595 | have special variable types, and Perl needs to know whether to sort | |
596 | numerically (where 99 is less than 100) or alphabetically (where 100 comes | |
597 | before 99). | |
598 | .IP "Boolean logic" 4 | |
599 | .IX Item "Boolean logic" | |
600 | .Vb 3 | |
601 | \& && and | |
602 | \& || or | |
603 | \& ! not | |
604 | .Ve | |
605 | .Sp | |
606 | (\f(CW\*(C`and\*(C'\fR, \f(CW\*(C`or\*(C'\fR and \f(CW\*(C`not\*(C'\fR aren't just in the above table as descriptions | |
607 | of the operators \*(-- they're also supported as operators in their own | |
608 | right. They're more readable than the C\-style operators, but have | |
609 | different precedence to \f(CW\*(C`&&\*(C'\fR and friends. Check perlop for more | |
610 | detail.) | |
611 | .IP "Miscellaneous" 4 | |
612 | .IX Item "Miscellaneous" | |
613 | .Vb 4 | |
614 | \& = assignment | |
615 | \& . string concatenation | |
616 | \& x string multiplication | |
617 | \& .. range operator (creates a list of numbers) | |
618 | .Ve | |
619 | .PP | |
620 | Many operators can be combined with a \f(CW\*(C`=\*(C'\fR as follows: | |
621 | .PP | |
622 | .Vb 3 | |
623 | \& $a += 1; # same as $a = $a + 1 | |
624 | \& $a -= 1; # same as $a = $a - 1 | |
625 | \& $a .= "\en"; # same as $a = $a . "\en"; | |
626 | .Ve | |
627 | .Sh "Files and I/O" | |
628 | .IX Subsection "Files and I/O" | |
629 | You can open a file for input or output using the \f(CW\*(C`open()\*(C'\fR function. | |
630 | It's documented in extravagant detail in perlfunc and perlopentut, | |
631 | but in short: | |
632 | .PP | |
633 | .Vb 3 | |
634 | \& open(INFILE, "input.txt") or die "Can't open input.txt: $!"; | |
635 | \& open(OUTFILE, ">output.txt") or die "Can't open output.txt: $!"; | |
636 | \& open(LOGFILE, ">>my.log") or die "Can't open logfile: $!"; | |
637 | .Ve | |
638 | .PP | |
639 | You can read from an open filehandle using the \f(CW\*(C`<>\*(C'\fR operator. In | |
640 | scalar context it reads a single line from the filehandle, and in list | |
641 | context it reads the whole file in, assigning each line to an element of | |
642 | the list: | |
643 | .PP | |
644 | .Vb 2 | |
645 | \& my $line = <INFILE>; | |
646 | \& my @lines = <INFILE>; | |
647 | .Ve | |
648 | .PP | |
649 | Reading in the whole file at one time is called slurping. It can | |
650 | be useful but it may be a memory hog. Most text file processing | |
651 | can be done a line at a time with Perl's looping constructs. | |
652 | .PP | |
653 | The \f(CW\*(C`<>\*(C'\fR operator is most often seen in a \f(CW\*(C`while\*(C'\fR loop: | |
654 | .PP | |
655 | .Vb 3 | |
656 | \& while (<INFILE>) { # assigns each line in turn to $_ | |
657 | \& print "Just read in this line: $_"; | |
658 | \& } | |
659 | .Ve | |
660 | .PP | |
661 | We've already seen how to print to standard output using \f(CW\*(C`print()\*(C'\fR. | |
662 | However, \f(CW\*(C`print()\*(C'\fR can also take an optional first argument specifying | |
663 | which filehandle to print to: | |
664 | .PP | |
665 | .Vb 3 | |
666 | \& print STDERR "This is your final warning.\en"; | |
667 | \& print OUTFILE $record; | |
668 | \& print LOGFILE $logmessage; | |
669 | .Ve | |
670 | .PP | |
671 | When you're done with your filehandles, you should \f(CW\*(C`close()\*(C'\fR them | |
672 | (though to be honest, Perl will clean up after you if you forget): | |
673 | .PP | |
674 | .Vb 1 | |
675 | \& close INFILE; | |
676 | .Ve | |
677 | .Sh "Regular expressions" | |
678 | .IX Subsection "Regular expressions" | |
679 | Perl's regular expression support is both broad and deep, and is the | |
680 | subject of lengthy documentation in perlrequick, perlretut, and | |
681 | elsewhere. However, in short: | |
682 | .IP "Simple matching" 4 | |
683 | .IX Item "Simple matching" | |
684 | .Vb 2 | |
685 | \& if (/foo/) { ... } # true if $_ contains "foo" | |
686 | \& if ($a =~ /foo/) { ... } # true if $a contains "foo" | |
687 | .Ve | |
688 | .Sp | |
689 | The \f(CW\*(C`//\*(C'\fR matching operator is documented in perlop. It operates on | |
690 | \&\f(CW$_\fR by default, or can be bound to another variable using the \f(CW\*(C`=~\*(C'\fR | |
691 | binding operator (also documented in perlop). | |
692 | .IP "Simple substitution" 4 | |
693 | .IX Item "Simple substitution" | |
694 | .Vb 3 | |
695 | \& s/foo/bar/; # replaces foo with bar in $_ | |
696 | \& $a =~ s/foo/bar/; # replaces foo with bar in $a | |
697 | \& $a =~ s/foo/bar/g; # replaces ALL INSTANCES of foo with bar in $a | |
698 | .Ve | |
699 | .Sp | |
700 | The \f(CW\*(C`s///\*(C'\fR substitution operator is documented in perlop. | |
701 | .IP "More complex regular expressions" 4 | |
702 | .IX Item "More complex regular expressions" | |
703 | You don't just have to match on fixed strings. In fact, you can match | |
704 | on just about anything you could dream of by using more complex regular | |
705 | expressions. These are documented at great length in perlre, but for | |
706 | the meantime, here's a quick cheat sheet: | |
707 | .Sp | |
708 | .Vb 10 | |
709 | \& . a single character | |
710 | \& \es a whitespace character (space, tab, newline) | |
711 | \& \eS non-whitespace character | |
712 | \& \ed a digit (0-9) | |
713 | \& \eD a non-digit | |
714 | \& \ew a word character (a-z, A-Z, 0-9, _) | |
715 | \& \eW a non-word character | |
716 | \& [aeiou] matches a single character in the given set | |
717 | \& [^aeiou] matches a single character outside the given set | |
718 | \& (foo|bar|baz) matches any of the alternatives specified | |
719 | .Ve | |
720 | .Sp | |
721 | .Vb 2 | |
722 | \& ^ start of string | |
723 | \& $ end of string | |
724 | .Ve | |
725 | .Sp | |
726 | Quantifiers can be used to specify how many of the previous thing you | |
727 | want to match on, where \*(L"thing\*(R" means either a literal character, one | |
728 | of the metacharacters listed above, or a group of characters or | |
729 | metacharacters in parentheses. | |
730 | .Sp | |
731 | .Vb 6 | |
732 | \& * zero or more of the previous thing | |
733 | \& + one or more of the previous thing | |
734 | \& ? zero or one of the previous thing | |
735 | \& {3} matches exactly 3 of the previous thing | |
736 | \& {3,6} matches between 3 and 6 of the previous thing | |
737 | \& {3,} matches 3 or more of the previous thing | |
738 | .Ve | |
739 | .Sp | |
740 | Some brief examples: | |
741 | .Sp | |
742 | .Vb 6 | |
743 | \& /^\ed+/ string starts with one or more digits | |
744 | \& /^$/ nothing in the string (start and end are adjacent) | |
745 | \& /(\ed\es){3}/ a three digits, each followed by a whitespace | |
746 | \& character (eg "3 4 5 ") | |
747 | \& /(a.)+/ matches a string in which every odd-numbered letter | |
748 | \& is a (eg "abacadaf") | |
749 | .Ve | |
750 | .Sp | |
751 | .Vb 5 | |
752 | \& # This loop reads from STDIN, and prints non-blank lines: | |
753 | \& while (<>) { | |
754 | \& next if /^$/; | |
755 | \& print; | |
756 | \& } | |
757 | .Ve | |
758 | .IP "Parentheses for capturing" 4 | |
759 | .IX Item "Parentheses for capturing" | |
760 | As well as grouping, parentheses serve a second purpose. They can be | |
761 | used to capture the results of parts of the regexp match for later use. | |
762 | The results end up in \f(CW$1\fR, \f(CW$2\fR and so on. | |
763 | .Sp | |
764 | .Vb 1 | |
765 | \& # a cheap and nasty way to break an email address up into parts | |
766 | .Ve | |
767 | .Sp | |
768 | .Vb 4 | |
769 | \& if ($email =~ /([^@])+@(.+)/) { | |
770 | \& print "Username is $1\en"; | |
771 | \& print "Hostname is $2\en"; | |
772 | \& } | |
773 | .Ve | |
774 | .IP "Other regexp features" 4 | |
775 | .IX Item "Other regexp features" | |
776 | Perl regexps also support backreferences, lookaheads, and all kinds of | |
777 | other complex details. Read all about them in perlrequick, | |
778 | perlretut, and perlre. | |
779 | .Sh "Writing subroutines" | |
780 | .IX Subsection "Writing subroutines" | |
781 | Writing subroutines is easy: | |
782 | .PP | |
783 | .Vb 4 | |
784 | \& sub log { | |
785 | \& my $logmessage = shift; | |
786 | \& print LOGFILE $logmessage; | |
787 | \& } | |
788 | .Ve | |
789 | .PP | |
790 | What's that \f(CW\*(C`shift\*(C'\fR? Well, the arguments to a subroutine are available | |
791 | to us as a special array called \f(CW@_\fR (see perlvar for more on that). | |
792 | The default argument to the \f(CW\*(C`shift\*(C'\fR function just happens to be \f(CW@_\fR. | |
793 | So \f(CW\*(C`my $logmessage = shift;\*(C'\fR shifts the first item off the list of | |
794 | arguments and assigns it to \f(CW$logmessage\fR. | |
795 | .PP | |
796 | We can manipulate \f(CW@_\fR in other ways too: | |
797 | .PP | |
798 | .Vb 2 | |
799 | \& my ($logmessage, $priority) = @_; # common | |
800 | \& my $logmessage = $_[0]; # uncommon, and ugly | |
801 | .Ve | |
802 | .PP | |
803 | Subroutines can also return values: | |
804 | .PP | |
805 | .Vb 5 | |
806 | \& sub square { | |
807 | \& my $num = shift; | |
808 | \& my $result = $num * $num; | |
809 | \& return $result; | |
810 | \& } | |
811 | .Ve | |
812 | .PP | |
813 | For more information on writing subroutines, see perlsub. | |
814 | .Sh "\s-1OO\s0 Perl" | |
815 | .IX Subsection "OO Perl" | |
816 | \&\s-1OO\s0 Perl is relatively simple and is implemented using references which | |
817 | know what sort of object they are based on Perl's concept of packages. | |
818 | However, \s-1OO\s0 Perl is largely beyond the scope of this document. | |
819 | Read perlboot, perltoot, perltooc and perlobj. | |
820 | .PP | |
821 | As a beginning Perl programmer, your most common use of \s-1OO\s0 Perl will be | |
822 | in using third-party modules, which are documented below. | |
823 | .Sh "Using Perl modules" | |
824 | .IX Subsection "Using Perl modules" | |
825 | Perl modules provide a range of features to help you avoid reinventing | |
826 | the wheel, and can be downloaded from \s-1CPAN\s0 ( http://www.cpan.org/ ). A | |
827 | number of popular modules are included with the Perl distribution | |
828 | itself. | |
829 | .PP | |
830 | Categories of modules range from text manipulation to network protocols | |
831 | to database integration to graphics. A categorized list of modules is | |
832 | also available from \s-1CPAN\s0. | |
833 | .PP | |
834 | To learn how to install modules you download from \s-1CPAN\s0, read | |
835 | perlmodinstall | |
836 | .PP | |
837 | To learn how to use a particular module, use \f(CW\*(C`perldoc \f(CIModule::Name\f(CW\*(C'\fR. | |
838 | Typically you will want to \f(CW\*(C`use \f(CIModule::Name\f(CW\*(C'\fR, which will then give | |
839 | you access to exported functions or an \s-1OO\s0 interface to the module. | |
840 | .PP | |
841 | perlfaq contains questions and answers related to many common | |
842 | tasks, and often provides suggestions for good \s-1CPAN\s0 modules to use. | |
843 | .PP | |
844 | perlmod describes Perl modules in general. perlmodlib lists the | |
845 | modules which came with your Perl installation. | |
846 | .PP | |
847 | If you feel the urge to write Perl modules, perlnewmod will give you | |
848 | good advice. | |
849 | .SH "AUTHOR" | |
850 | .IX Header "AUTHOR" | |
851 | Kirrily \*(L"Skud\*(R" Robert <skud@cpan.org> |