| 1 | .\" Automatically generated by Pod::Man v1.34, Pod::Parser v1.13 |
| 2 | .\" |
| 3 | .\" Standard preamble: |
| 4 | .\" ======================================================================== |
| 5 | .de Sh \" Subsection heading |
| 6 | .br |
| 7 | .if t .Sp |
| 8 | .ne 5 |
| 9 | .PP |
| 10 | \fB\\$1\fR |
| 11 | .PP |
| 12 | .. |
| 13 | .de Sp \" Vertical space (when we can't use .PP) |
| 14 | .if t .sp .5v |
| 15 | .if n .sp |
| 16 | .. |
| 17 | .de Vb \" Begin verbatim text |
| 18 | .ft CW |
| 19 | .nf |
| 20 | .ne \\$1 |
| 21 | .. |
| 22 | .de Ve \" End verbatim text |
| 23 | .ft R |
| 24 | .fi |
| 25 | .. |
| 26 | .\" Set up some character translations and predefined strings. \*(-- will |
| 27 | .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left |
| 28 | .\" double quote, and \*(R" will give a right double quote. | will give a |
| 29 | .\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to |
| 30 | .\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C' |
| 31 | .\" expand to `' in nroff, nothing in troff, for use with C<>. |
| 32 | .tr \(*W-|\(bv\*(Tr |
| 33 | .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' |
| 34 | .ie n \{\ |
| 35 | . ds -- \(*W- |
| 36 | . ds PI pi |
| 37 | . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch |
| 38 | . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch |
| 39 | . ds L" "" |
| 40 | . ds R" "" |
| 41 | . ds C` "" |
| 42 | . ds C' "" |
| 43 | 'br\} |
| 44 | .el\{\ |
| 45 | . ds -- \|\(em\| |
| 46 | . ds PI \(*p |
| 47 | . ds L" `` |
| 48 | . ds R" '' |
| 49 | 'br\} |
| 50 | .\" |
| 51 | .\" If the F register is turned on, we'll generate index entries on stderr for |
| 52 | .\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index |
| 53 | .\" entries marked with X<> in POD. Of course, you'll have to process the |
| 54 | .\" output yourself in some meaningful fashion. |
| 55 | .if \nF \{\ |
| 56 | . de IX |
| 57 | . tm Index:\\$1\t\\n%\t"\\$2" |
| 58 | .. |
| 59 | . nr % 0 |
| 60 | . rr F |
| 61 | .\} |
| 62 | .\" |
| 63 | .\" For nroff, turn off justification. Always turn off hyphenation; it makes |
| 64 | .\" way too many mistakes in technical documents. |
| 65 | .hy 0 |
| 66 | .if n .na |
| 67 | .\" |
| 68 | .\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). |
| 69 | .\" Fear. Run. Save yourself. No user-serviceable parts. |
| 70 | . \" fudge factors for nroff and troff |
| 71 | .if n \{\ |
| 72 | . ds #H 0 |
| 73 | . ds #V .8m |
| 74 | . ds #F .3m |
| 75 | . ds #[ \f1 |
| 76 | . ds #] \fP |
| 77 | .\} |
| 78 | .if t \{\ |
| 79 | . ds #H ((1u-(\\\\n(.fu%2u))*.13m) |
| 80 | . ds #V .6m |
| 81 | . ds #F 0 |
| 82 | . ds #[ \& |
| 83 | . ds #] \& |
| 84 | .\} |
| 85 | . \" simple accents for nroff and troff |
| 86 | .if n \{\ |
| 87 | . ds ' \& |
| 88 | . ds ` \& |
| 89 | . ds ^ \& |
| 90 | . ds , \& |
| 91 | . ds ~ ~ |
| 92 | . ds / |
| 93 | .\} |
| 94 | .if t \{\ |
| 95 | . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" |
| 96 | . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' |
| 97 | . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' |
| 98 | . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' |
| 99 | . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' |
| 100 | . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' |
| 101 | .\} |
| 102 | . \" troff and (daisy-wheel) nroff accents |
| 103 | .ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V' |
| 104 | .ds 8 \h'\*(#H'\(*b\h'-\*(#H' |
| 105 | .ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#] |
| 106 | .ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H' |
| 107 | .ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u' |
| 108 | .ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#] |
| 109 | .ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#] |
| 110 | .ds ae a\h'-(\w'a'u*4/10)'e |
| 111 | .ds Ae A\h'-(\w'A'u*4/10)'E |
| 112 | . \" corrections for vroff |
| 113 | .if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u' |
| 114 | .if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u' |
| 115 | . \" for low resolution devices (crt and lpr) |
| 116 | .if \n(.H>23 .if \n(.V>19 \ |
| 117 | \{\ |
| 118 | . ds : e |
| 119 | . ds 8 ss |
| 120 | . ds o a |
| 121 | . ds d- d\h'-1'\(ga |
| 122 | . ds D- D\h'-1'\(hy |
| 123 | . ds th \o'bp' |
| 124 | . ds Th \o'LP' |
| 125 | . ds ae ae |
| 126 | . ds Ae AE |
| 127 | .\} |
| 128 | .rm #[ #] #H #V #F C |
| 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 | \& print |
| 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> |