| 1 | =head1 NAME |
| 2 | |
| 3 | perltrap - Perl traps for the unwary |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | The biggest trap of all is forgetting to use the B<-w> switch; see |
| 8 | L<perlrun>. The second biggest trap is not making your entire program |
| 9 | runnable under C<use strict>. |
| 10 | |
| 11 | =head2 Awk Traps |
| 12 | |
| 13 | Accustomed B<awk> users should take special note of the following: |
| 14 | |
| 15 | =over 4 |
| 16 | |
| 17 | =item * |
| 18 | |
| 19 | The English module, loaded via |
| 20 | |
| 21 | use English; |
| 22 | |
| 23 | allows you to refer to special variables (like $RS) as |
| 24 | though they were in B<awk>; see L<perlvar> for details. |
| 25 | |
| 26 | =item * |
| 27 | |
| 28 | Semicolons are required after all simple statements in Perl (except |
| 29 | at the end of a block). Newline is not a statement delimiter. |
| 30 | |
| 31 | =item * |
| 32 | |
| 33 | Curly brackets are required on C<if>s and C<while>s. |
| 34 | |
| 35 | =item * |
| 36 | |
| 37 | Variables begin with "$" or "@" in Perl. |
| 38 | |
| 39 | =item * |
| 40 | |
| 41 | Arrays index from 0. Likewise string positions in substr() and |
| 42 | index(). |
| 43 | |
| 44 | =item * |
| 45 | |
| 46 | You have to decide whether your array has numeric or string indices. |
| 47 | |
| 48 | =item * |
| 49 | |
| 50 | Associative array values do not spring into existence upon mere |
| 51 | reference. |
| 52 | |
| 53 | =item * |
| 54 | |
| 55 | You have to decide whether you want to use string or numeric |
| 56 | comparisons. |
| 57 | |
| 58 | =item * |
| 59 | |
| 60 | Reading an input line does not split it for you. You get to split it |
| 61 | yourself to an array. And the split() operator has different |
| 62 | arguments. |
| 63 | |
| 64 | =item * |
| 65 | |
| 66 | The current input line is normally in $_, not $0. It generally does |
| 67 | not have the newline stripped. ($0 is the name of the program |
| 68 | executed.) See L<perlvar>. |
| 69 | |
| 70 | =item * |
| 71 | |
| 72 | $<I<digit>> does not refer to fields--it refers to substrings matched by |
| 73 | the last match pattern. |
| 74 | |
| 75 | =item * |
| 76 | |
| 77 | The print() statement does not add field and record separators unless |
| 78 | you set C<$,> and C<$.>. You can set $OFS and $ORS if you're using |
| 79 | the English module. |
| 80 | |
| 81 | =item * |
| 82 | |
| 83 | You must open your files before you print to them. |
| 84 | |
| 85 | =item * |
| 86 | |
| 87 | The range operator is "..", not comma. The comma operator works as in |
| 88 | C. |
| 89 | |
| 90 | =item * |
| 91 | |
| 92 | The match operator is "=~", not "~". ("~" is the one's complement |
| 93 | operator, as in C.) |
| 94 | |
| 95 | =item * |
| 96 | |
| 97 | The exponentiation operator is "**", not "^". "^" is the XOR |
| 98 | operator, as in C. (You know, one could get the feeling that B<awk> is |
| 99 | basically incompatible with C.) |
| 100 | |
| 101 | =item * |
| 102 | |
| 103 | The concatenation operator is ".", not the null string. (Using the |
| 104 | null string would render C</pat/ /pat/> unparsable, since the third slash |
| 105 | would be interpreted as a division operator--the tokener is in fact |
| 106 | slightly context sensitive for operators like "/", "?", and ">". |
| 107 | And in fact, "." itself can be the beginning of a number.) |
| 108 | |
| 109 | =item * |
| 110 | |
| 111 | The C<next>, C<exit>, and C<continue> keywords work differently. |
| 112 | |
| 113 | =item * |
| 114 | |
| 115 | |
| 116 | The following variables work differently: |
| 117 | |
| 118 | Awk Perl |
| 119 | ARGC $#ARGV or scalar @ARGV |
| 120 | ARGV[0] $0 |
| 121 | FILENAME $ARGV |
| 122 | FNR $. - something |
| 123 | FS (whatever you like) |
| 124 | NF $#Fld, or some such |
| 125 | NR $. |
| 126 | OFMT $# |
| 127 | OFS $, |
| 128 | ORS $\ |
| 129 | RLENGTH length($&) |
| 130 | RS $/ |
| 131 | RSTART length($`) |
| 132 | SUBSEP $; |
| 133 | |
| 134 | =item * |
| 135 | |
| 136 | You cannot set $RS to a pattern, only a string. |
| 137 | |
| 138 | =item * |
| 139 | |
| 140 | When in doubt, run the B<awk> construct through B<a2p> and see what it |
| 141 | gives you. |
| 142 | |
| 143 | =back |
| 144 | |
| 145 | =head2 C Traps |
| 146 | |
| 147 | Cerebral C programmers should take note of the following: |
| 148 | |
| 149 | =over 4 |
| 150 | |
| 151 | =item * |
| 152 | |
| 153 | Curly brackets are required on C<if>'s and C<while>'s. |
| 154 | |
| 155 | =item * |
| 156 | |
| 157 | You must use C<elsif> rather than C<else if>. |
| 158 | |
| 159 | =item * |
| 160 | |
| 161 | The C<break> and C<continue> keywords from C become in |
| 162 | Perl C<last> and C<next>, respectively. |
| 163 | Unlike in C, these do I<NOT> work within a C<do { } while> construct. |
| 164 | |
| 165 | =item * |
| 166 | |
| 167 | There's no switch statement. (But it's easy to build one on the fly.) |
| 168 | |
| 169 | =item * |
| 170 | |
| 171 | Variables begin with "$" or "@" in Perl. |
| 172 | |
| 173 | =item * |
| 174 | |
| 175 | C<printf()> does not implement the "*" format for interpolating |
| 176 | field widths, but it's trivial to use interpolation of double-quoted |
| 177 | strings to achieve the same effect. |
| 178 | |
| 179 | =item * |
| 180 | |
| 181 | Comments begin with "#", not "/*". |
| 182 | |
| 183 | =item * |
| 184 | |
| 185 | You can't take the address of anything, although a similar operator |
| 186 | in Perl 5 is the backslash, which creates a reference. |
| 187 | |
| 188 | =item * |
| 189 | |
| 190 | C<ARGV> must be capitalized. C<$ARGV[0]> is C's C<argv[1]>, and C<argv[0]> |
| 191 | ends up in C<$0>. |
| 192 | |
| 193 | =item * |
| 194 | |
| 195 | System calls such as link(), unlink(), rename(), etc. return nonzero for |
| 196 | success, not 0. |
| 197 | |
| 198 | =item * |
| 199 | |
| 200 | Signal handlers deal with signal names, not numbers. Use C<kill -l> |
| 201 | to find their names on your system. |
| 202 | |
| 203 | =back |
| 204 | |
| 205 | =head2 Sed Traps |
| 206 | |
| 207 | Seasoned B<sed> programmers should take note of the following: |
| 208 | |
| 209 | =over 4 |
| 210 | |
| 211 | =item * |
| 212 | |
| 213 | Backreferences in substitutions use "$" rather than "\". |
| 214 | |
| 215 | =item * |
| 216 | |
| 217 | The pattern matching metacharacters "(", ")", and "|" do not have backslashes |
| 218 | in front. |
| 219 | |
| 220 | =item * |
| 221 | |
| 222 | The range operator is C<...>, rather than comma. |
| 223 | |
| 224 | =back |
| 225 | |
| 226 | =head2 Shell Traps |
| 227 | |
| 228 | Sharp shell programmers should take note of the following: |
| 229 | |
| 230 | =over 4 |
| 231 | |
| 232 | =item * |
| 233 | |
| 234 | The backtick operator does variable interpolation without regard to |
| 235 | the presence of single quotes in the command. |
| 236 | |
| 237 | =item * |
| 238 | |
| 239 | The backtick operator does no translation of the return value, unlike B<csh>. |
| 240 | |
| 241 | =item * |
| 242 | |
| 243 | Shells (especially B<csh>) do several levels of substitution on each |
| 244 | command line. Perl does substitution only in certain constructs |
| 245 | such as double quotes, backticks, angle brackets, and search patterns. |
| 246 | |
| 247 | =item * |
| 248 | |
| 249 | Shells interpret scripts a little bit at a time. Perl compiles the |
| 250 | entire program before executing it (except for C<BEGIN> blocks, which |
| 251 | execute at compile time). |
| 252 | |
| 253 | =item * |
| 254 | |
| 255 | The arguments are available via @ARGV, not $1, $2, etc. |
| 256 | |
| 257 | =item * |
| 258 | |
| 259 | The environment is not automatically made available as separate scalar |
| 260 | variables. |
| 261 | |
| 262 | =back |
| 263 | |
| 264 | =head2 Perl Traps |
| 265 | |
| 266 | Practicing Perl Programmers should take note of the following: |
| 267 | |
| 268 | =over 4 |
| 269 | |
| 270 | =item * |
| 271 | |
| 272 | Remember that many operations behave differently in a list |
| 273 | context than they do in a scalar one. See L<perldata> for details. |
| 274 | |
| 275 | =item * |
| 276 | |
| 277 | Avoid barewords if you can, especially all lower-case ones. |
| 278 | You can't tell just by looking at it whether a bareword is |
| 279 | a function or a string. By using quotes on strings and |
| 280 | parens on function calls, you won't ever get them confused. |
| 281 | |
| 282 | =item * |
| 283 | |
| 284 | You cannot discern from mere inspection which built-ins |
| 285 | are unary operators (like chop() and chdir()) |
| 286 | and which are list operators (like print() and unlink()). |
| 287 | (User-defined subroutines can B<only> be list operators, never |
| 288 | unary ones.) See L<perlop>. |
| 289 | |
| 290 | =item * |
| 291 | |
| 292 | People have a hard time remembering that some functions |
| 293 | default to $_, or @ARGV, or whatever, but that others which |
| 294 | you might expect to do not. |
| 295 | |
| 296 | =item * |
| 297 | |
| 298 | The <FH> construct is not the name of the filehandle, it is a readline |
| 299 | operation on that handle. The data read is only assigned to $_ if the |
| 300 | file read is the sole condition in a while loop: |
| 301 | |
| 302 | while (<FH>) { } |
| 303 | while ($_ = <FH>) { }.. |
| 304 | <FH>; # data discarded! |
| 305 | |
| 306 | =item * |
| 307 | |
| 308 | Remember not to use "C<=>" when you need "C<=~>"; |
| 309 | these two constructs are quite different: |
| 310 | |
| 311 | $x = /foo/; |
| 312 | $x =~ /foo/; |
| 313 | |
| 314 | =item * |
| 315 | |
| 316 | The C<do {}> construct isn't a real loop that you can use |
| 317 | loop control on. |
| 318 | |
| 319 | =item * |
| 320 | |
| 321 | Use C<my()> for local variables whenever you can get away with |
| 322 | it (but see L<perlform> for where you can't). |
| 323 | Using C<local()> actually gives a local value to a global |
| 324 | variable, which leaves you open to unforeseen side-effects |
| 325 | of dynamic scoping. |
| 326 | |
| 327 | =item * |
| 328 | |
| 329 | If you localize an exported variable in a module, its exported value will |
| 330 | not change. The local name becomes an alias to a new value but the |
| 331 | external name is still an alias for the original. |
| 332 | |
| 333 | =back |
| 334 | |
| 335 | =head2 Perl4 to Perl5 Traps |
| 336 | |
| 337 | Practicing Perl4 Programmers should take note of the following |
| 338 | Perl4-to-Perl5 specific traps. |
| 339 | |
| 340 | They're crudely ordered according to the following list: |
| 341 | |
| 342 | =over 4 |
| 343 | |
| 344 | =item Discontinuance, Deprecation, and BugFix traps |
| 345 | |
| 346 | Anything that's been fixed as a perl4 bug, removed as a perl4 feature |
| 347 | or deprecated as a perl4 feature with the intent to encourage usage of |
| 348 | some other perl5 feature. |
| 349 | |
| 350 | =item Parsing Traps |
| 351 | |
| 352 | Traps that appear to stem from the new parser. |
| 353 | |
| 354 | =item Numerical Traps |
| 355 | |
| 356 | Traps having to do with numerical or mathematical operators. |
| 357 | |
| 358 | =item General data type traps |
| 359 | |
| 360 | Traps involving perl standard data types. |
| 361 | |
| 362 | =item Context Traps - scalar, list contexts |
| 363 | |
| 364 | Traps related to context within lists, scalar statements/declarations. |
| 365 | |
| 366 | =item Precedence Traps |
| 367 | |
| 368 | Traps related to the precedence of parsing, evaluation, and execution of |
| 369 | code. |
| 370 | |
| 371 | =item General Regular Expression Traps using s///, etc. |
| 372 | |
| 373 | Traps related to the use of pattern matching. |
| 374 | |
| 375 | =item Subroutine, Signal, Sorting Traps |
| 376 | |
| 377 | Traps related to the use of signals and signal handlers, general subroutines, |
| 378 | and sorting, along with sorting subroutines. |
| 379 | |
| 380 | =item OS Traps |
| 381 | |
| 382 | OS-specific traps. |
| 383 | |
| 384 | =item DBM Traps |
| 385 | |
| 386 | Traps specific to the use of C<dbmopen()>, and specific dbm implementations. |
| 387 | |
| 388 | =item Unclassified Traps |
| 389 | |
| 390 | Everything else. |
| 391 | |
| 392 | =back |
| 393 | |
| 394 | If you find an example of a conversion trap that is not listed here, |
| 395 | please submit it to Bill Middleton F<wjm@best.com> for inclusion. |
| 396 | Also note that at least some of these can be caught with C<-w>. |
| 397 | |
| 398 | =head2 Discontinuance, Deprecation, and BugFix traps |
| 399 | |
| 400 | Anything that has been discontinued, deprecated, or fixed as |
| 401 | a bug from perl4. |
| 402 | |
| 403 | =over 4 |
| 404 | |
| 405 | =item * Discontinuance |
| 406 | |
| 407 | Symbols starting with "_" are no longer forced into package main, except |
| 408 | for C<$_> itself (and C<@_>, etc.). |
| 409 | |
| 410 | package test; |
| 411 | $_legacy = 1; |
| 412 | |
| 413 | package main; |
| 414 | print "\$_legacy is ",$_legacy,"\n"; |
| 415 | |
| 416 | # perl4 prints: $_legacy is 1 |
| 417 | # perl5 prints: $_legacy is |
| 418 | |
| 419 | =item * Deprecation |
| 420 | |
| 421 | Double-colon is now a valid package separator in a variable name. Thus these |
| 422 | behave differently in perl4 vs. perl5, since the packages don't exist. |
| 423 | |
| 424 | $a=1;$b=2;$c=3;$var=4; |
| 425 | print "$a::$b::$c "; |
| 426 | print "$var::abc::xyz\n"; |
| 427 | |
| 428 | # perl4 prints: 1::2::3 4::abc::xyz |
| 429 | # perl5 prints: 3 |
| 430 | |
| 431 | Given that C<::> is now the preferred package delimiter, it is debatable |
| 432 | whether this should be classed as a bug or not. |
| 433 | (The older package delimiter, ' ,is used here) |
| 434 | |
| 435 | $x = 10 ; |
| 436 | print "x=${'x}\n" ; |
| 437 | |
| 438 | # perl4 prints: x=10 |
| 439 | # perl5 prints: Can't find string terminator "'" anywhere before EOF |
| 440 | |
| 441 | Also see precedence traps, for parsing C<$:>. |
| 442 | |
| 443 | =item * BugFix |
| 444 | |
| 445 | The second and third arguments of C<splice()> are now evaluated in scalar |
| 446 | context (as the Camel says) rather than list context. |
| 447 | |
| 448 | sub sub1{return(0,2) } # return a 2-elem array |
| 449 | sub sub2{ return(1,2,3)} # return a 3-elem array |
| 450 | @a1 = ("a","b","c","d","e"); |
| 451 | @a2 = splice(@a1,&sub1,&sub2); |
| 452 | print join(' ',@a2),"\n"; |
| 453 | |
| 454 | # perl4 prints: a b |
| 455 | # perl5 prints: c d e |
| 456 | |
| 457 | =item * Discontinuance |
| 458 | |
| 459 | You can't do a C<goto> into a block that is optimized away. Darn. |
| 460 | |
| 461 | goto marker1; |
| 462 | |
| 463 | for(1){ |
| 464 | marker1: |
| 465 | print "Here I is!\n"; |
| 466 | } |
| 467 | |
| 468 | # perl4 prints: Here I is! |
| 469 | # perl5 dumps core (SEGV) |
| 470 | |
| 471 | =item * Discontinuance |
| 472 | |
| 473 | It is no longer syntactically legal to use whitespace as the name |
| 474 | of a variable, or as a delimiter for any kind of quote construct. |
| 475 | Double darn. |
| 476 | |
| 477 | $a = ("foo bar"); |
| 478 | $b = q baz ; |
| 479 | print "a is $a, b is $b\n"; |
| 480 | |
| 481 | # perl4 prints: a is foo bar, b is baz |
| 482 | # perl5 errors: Bare word found where operator expected |
| 483 | |
| 484 | =item * Discontinuance |
| 485 | |
| 486 | The archaic while/if BLOCK BLOCK syntax is no longer supported. |
| 487 | |
| 488 | if { 1 } { |
| 489 | print "True!"; |
| 490 | } |
| 491 | else { |
| 492 | print "False!"; |
| 493 | } |
| 494 | |
| 495 | # perl4 prints: True! |
| 496 | # perl5 errors: syntax error at test.pl line 1, near "if {" |
| 497 | |
| 498 | =item * BugFix |
| 499 | |
| 500 | The C<**> operator now binds more tightly than unary minus. |
| 501 | It was documented to work this way before, but didn't. |
| 502 | |
| 503 | print -4**2,"\n"; |
| 504 | |
| 505 | # perl4 prints: 16 |
| 506 | # perl5 prints: -16 |
| 507 | |
| 508 | =item * Discontinuance |
| 509 | |
| 510 | The meaning of C<foreach{}> has changed slightly when it is iterating over a |
| 511 | list which is not an array. This used to assign the list to a |
| 512 | temporary array, but no longer does so (for efficiency). This means |
| 513 | that you'll now be iterating over the actual values, not over copies of |
| 514 | the values. Modifications to the loop variable can change the original |
| 515 | values. |
| 516 | |
| 517 | @list = ('ab','abc','bcd','def'); |
| 518 | foreach $var (grep(/ab/,@list)){ |
| 519 | $var = 1; |
| 520 | } |
| 521 | print (join(':',@list)); |
| 522 | |
| 523 | # perl4 prints: ab:abc:bcd:def |
| 524 | # perl5 prints: 1:1:bcd:def |
| 525 | |
| 526 | To retain Perl4 semantics you need to assign your list |
| 527 | explicitly to a temporary array and then iterate over that. For |
| 528 | example, you might need to change |
| 529 | |
| 530 | foreach $var (grep(/ab/,@list)){ |
| 531 | |
| 532 | to |
| 533 | |
| 534 | foreach $var (@tmp = grep(/ab/,@list)){ |
| 535 | |
| 536 | Otherwise changing $var will clobber the values of @list. (This most often |
| 537 | happens when you use C<$_> for the loop variable, and call subroutines in |
| 538 | the loop that don't properly localize C<$_>.) |
| 539 | |
| 540 | =item * Discontinuance |
| 541 | |
| 542 | C<split> with no arguments now behaves like C<split ' '> (which doesn't |
| 543 | return an initial null field if $_ starts with whitespace), it used to |
| 544 | behave like C<split /\s+/> (which does). |
| 545 | |
| 546 | $_ = ' hi mom'; |
| 547 | print join(':', split); |
| 548 | |
| 549 | # perl4 prints: :hi:mom |
| 550 | # perl5 prints: hi:mom |
| 551 | |
| 552 | =item * Deprecation |
| 553 | |
| 554 | Some error messages will be different. |
| 555 | |
| 556 | =item * Discontinuance |
| 557 | |
| 558 | Some bugs may have been inadvertently removed. :-) |
| 559 | |
| 560 | =back |
| 561 | |
| 562 | =head2 Parsing Traps |
| 563 | |
| 564 | Perl4-to-Perl5 traps from having to do with parsing. |
| 565 | |
| 566 | =over 4 |
| 567 | |
| 568 | =item * Parsing |
| 569 | |
| 570 | Note the space between . and = |
| 571 | |
| 572 | $string . = "more string"; |
| 573 | print $string; |
| 574 | |
| 575 | # perl4 prints: more string |
| 576 | # perl5 prints: syntax error at - line 1, near ". =" |
| 577 | |
| 578 | =item * Parsing |
| 579 | |
| 580 | Better parsing in perl 5 |
| 581 | |
| 582 | sub foo {} |
| 583 | &foo |
| 584 | print("hello, world\n"); |
| 585 | |
| 586 | # perl4 prints: hello, world |
| 587 | # perl5 prints: syntax error |
| 588 | |
| 589 | =item * Parsing |
| 590 | |
| 591 | "if it looks like a function, it is a function" rule. |
| 592 | |
| 593 | print |
| 594 | ($foo == 1) ? "is one\n" : "is zero\n"; |
| 595 | |
| 596 | # perl4 prints: is zero |
| 597 | # perl5 warns: "Useless use of a constant in void context" if using -w |
| 598 | |
| 599 | =back |
| 600 | |
| 601 | =head2 Numerical Traps |
| 602 | |
| 603 | Perl4-to-Perl5 traps having to do with numerical operators, |
| 604 | operands, or output from same. |
| 605 | |
| 606 | =over 5 |
| 607 | |
| 608 | =item * Numerical |
| 609 | |
| 610 | Formatted output and significant digits |
| 611 | |
| 612 | print 7.373504 - 0, "\n"; |
| 613 | printf "%20.18f\n", 7.373504 - 0; |
| 614 | |
| 615 | # Perl4 prints: |
| 616 | 7.375039999999996141 |
| 617 | 7.37503999999999614 |
| 618 | |
| 619 | # Perl5 prints: |
| 620 | 7.373504 |
| 621 | 7.37503999999999614 |
| 622 | |
| 623 | =item * Numerical |
| 624 | |
| 625 | This specific item has been deleted. It demonstrated how the autoincrement |
| 626 | operator would not catch when a number went over the signed int limit. Fixed |
| 627 | in 5.003_04. But always be wary when using large ints. If in doubt: |
| 628 | |
| 629 | use Math::BigInt; |
| 630 | |
| 631 | =item * Numerical |
| 632 | |
| 633 | Assignment of return values from numeric equality tests |
| 634 | does not work in perl5 when the test evaluates to false (0). |
| 635 | Logical tests now return an null, instead of 0 |
| 636 | |
| 637 | $p = ($test == 1); |
| 638 | print $p,"\n"; |
| 639 | |
| 640 | # perl4 prints: 0 |
| 641 | # perl5 prints: |
| 642 | |
| 643 | Also see the L<General Regular Expression Traps> tests for another example |
| 644 | of this new feature... |
| 645 | |
| 646 | =back |
| 647 | |
| 648 | =head2 General data type traps |
| 649 | |
| 650 | Perl4-to-Perl5 traps involving most data-types, and their usage |
| 651 | within certain expressions and/or context. |
| 652 | |
| 653 | =over 5 |
| 654 | |
| 655 | =item * (Arrays) |
| 656 | |
| 657 | Negative array subscripts now count from the end of the array. |
| 658 | |
| 659 | @a = (1, 2, 3, 4, 5); |
| 660 | print "The third element of the array is $a[3] also expressed as $a[-2] \n"; |
| 661 | |
| 662 | # perl4 prints: The third element of the array is 4 also expressed as |
| 663 | # perl5 prints: The third element of the array is 4 also expressed as 4 |
| 664 | |
| 665 | =item * (Arrays) |
| 666 | |
| 667 | Setting C<$#array> lower now discards array elements, and makes them |
| 668 | impossible to recover. |
| 669 | |
| 670 | @a = (a,b,c,d,e); |
| 671 | print "Before: ",join('',@a); |
| 672 | $#a =1; |
| 673 | print ", After: ",join('',@a); |
| 674 | $#a =3; |
| 675 | print ", Recovered: ",join('',@a),"\n"; |
| 676 | |
| 677 | # perl4 prints: Before: abcde, After: ab, Recovered: abcd |
| 678 | # perl5 prints: Before: abcde, After: ab, Recovered: ab |
| 679 | |
| 680 | =item * (Hashes) |
| 681 | |
| 682 | Hashes get defined before use |
| 683 | |
| 684 | local($s,@a,%h); |
| 685 | die "scalar \$s defined" if defined($s); |
| 686 | die "array \@a defined" if defined(@a); |
| 687 | die "hash \%h defined" if defined(%h); |
| 688 | |
| 689 | # perl4 prints: |
| 690 | # perl5 dies: hash %h defined |
| 691 | |
| 692 | =item * (Globs) |
| 693 | |
| 694 | glob assignment from variable to variable will fail if the assigned |
| 695 | variable is localized subsequent to the assignment |
| 696 | |
| 697 | @a = ("This is Perl 4"); |
| 698 | *b = *a; |
| 699 | local(@a); |
| 700 | print @b,"\n"; |
| 701 | |
| 702 | # perl4 prints: This is Perl 4 |
| 703 | # perl5 prints: |
| 704 | |
| 705 | # Another example |
| 706 | |
| 707 | *fred = *barney; # fred is aliased to barney |
| 708 | @barney = (1, 2, 4); |
| 709 | # @fred; |
| 710 | print "@fred"; # should print "1, 2, 4" |
| 711 | |
| 712 | # perl4 prints: 1 2 4 |
| 713 | # perl5 prints: Literal @fred now requires backslash |
| 714 | |
| 715 | =item * (Scalar String) |
| 716 | |
| 717 | Changes in unary negation (of strings) |
| 718 | This change effects both the return value and what it |
| 719 | does to auto(magic)increment. |
| 720 | |
| 721 | $x = "aaa"; |
| 722 | print ++$x," : "; |
| 723 | print -$x," : "; |
| 724 | print ++$x,"\n"; |
| 725 | |
| 726 | # perl4 prints: aab : -0 : 1 |
| 727 | # perl5 prints: aab : -aab : aac |
| 728 | |
| 729 | =item * (Constants) |
| 730 | |
| 731 | perl 4 lets you modify constants: |
| 732 | |
| 733 | $foo = "x"; |
| 734 | &mod($foo); |
| 735 | for ($x = 0; $x < 3; $x++) { |
| 736 | &mod("a"); |
| 737 | } |
| 738 | sub mod { |
| 739 | print "before: $_[0]"; |
| 740 | $_[0] = "m"; |
| 741 | print " after: $_[0]\n"; |
| 742 | } |
| 743 | |
| 744 | # perl4: |
| 745 | # before: x after: m |
| 746 | # before: a after: m |
| 747 | # before: m after: m |
| 748 | # before: m after: m |
| 749 | |
| 750 | # Perl5: |
| 751 | # before: x after: m |
| 752 | # Modification of a read-only value attempted at foo.pl line 12. |
| 753 | # before: a |
| 754 | |
| 755 | =item * (Scalars) |
| 756 | |
| 757 | The behavior is slightly different for: |
| 758 | |
| 759 | print "$x", defined $x |
| 760 | |
| 761 | # perl 4: 1 |
| 762 | # perl 5: <no output, $x is not called into existence> |
| 763 | |
| 764 | =item * (Variable Suicide) |
| 765 | |
| 766 | Variable suicide behavior is more consistent under Perl 5. |
| 767 | Perl5 exhibits the same behavior for associative arrays and scalars, |
| 768 | that perl4 exhibits only for scalars. |
| 769 | |
| 770 | $aGlobal{ "aKey" } = "global value"; |
| 771 | print "MAIN:", $aGlobal{"aKey"}, "\n"; |
| 772 | $GlobalLevel = 0; |
| 773 | &test( *aGlobal ); |
| 774 | |
| 775 | sub test { |
| 776 | local( *theArgument ) = @_; |
| 777 | local( %aNewLocal ); # perl 4 != 5.001l,m |
| 778 | $aNewLocal{"aKey"} = "this should never appear"; |
| 779 | print "SUB: ", $theArgument{"aKey"}, "\n"; |
| 780 | $aNewLocal{"aKey"} = "level $GlobalLevel"; # what should print |
| 781 | $GlobalLevel++; |
| 782 | if( $GlobalLevel<4 ) { |
| 783 | &test( *aNewLocal ); |
| 784 | } |
| 785 | } |
| 786 | |
| 787 | # Perl4: |
| 788 | # MAIN:global value |
| 789 | # SUB: global value |
| 790 | # SUB: level 0 |
| 791 | # SUB: level 1 |
| 792 | # SUB: level 2 |
| 793 | |
| 794 | # Perl5: |
| 795 | # MAIN:global value |
| 796 | # SUB: global value |
| 797 | # SUB: this should never appear |
| 798 | # SUB: this should never appear |
| 799 | # SUB: this should never appear |
| 800 | |
| 801 | =back |
| 802 | |
| 803 | =head2 Context Traps - scalar, list contexts |
| 804 | |
| 805 | =over 5 |
| 806 | |
| 807 | =item * (list context) |
| 808 | |
| 809 | The elements of argument lists for formats are now evaluated in list |
| 810 | context. This means you can interpolate list values now. |
| 811 | |
| 812 | @fmt = ("foo","bar","baz"); |
| 813 | format STDOUT= |
| 814 | @<<<<< @||||| @>>>>> |
| 815 | @fmt; |
| 816 | . |
| 817 | write; |
| 818 | |
| 819 | # perl4 errors: Please use commas to separate fields in file |
| 820 | # perl5 prints: foo bar baz |
| 821 | |
| 822 | =item * (scalar context) |
| 823 | |
| 824 | The C<caller()> function now returns a false value in a scalar context |
| 825 | if there is no caller. This lets library files determine if they're |
| 826 | being required. |
| 827 | |
| 828 | caller() ? (print "You rang?\n") : (print "Got a 0\n"); |
| 829 | |
| 830 | # perl4 errors: There is no caller |
| 831 | # perl5 prints: Got a 0 |
| 832 | |
| 833 | =item * (scalar context) |
| 834 | |
| 835 | The comma operator in a scalar context is now guaranteed to give a |
| 836 | scalar context to its arguments. |
| 837 | |
| 838 | @y= ('a','b','c'); |
| 839 | $x = (1, 2, @y); |
| 840 | print "x = $x\n"; |
| 841 | |
| 842 | # Perl4 prints: x = c # Thinks list context interpolates list |
| 843 | # Perl5 prints: x = 3 # Knows scalar uses length of list |
| 844 | |
| 845 | =item * (list, builtin) |
| 846 | |
| 847 | C<sprintf()> funkiness (array argument converted to scalar array count) |
| 848 | This test could be added to t/op/sprintf.t |
| 849 | |
| 850 | @z = ('%s%s', 'foo', 'bar'); |
| 851 | $x = sprintf(@z); |
| 852 | if ($x eq 'foobar') {print "ok 2\n";} else {print "not ok 2 '$x'\n";} |
| 853 | |
| 854 | # perl4 prints: ok 2 |
| 855 | # perl5 prints: not ok 2 |
| 856 | |
| 857 | C<printf()> works fine, though: |
| 858 | |
| 859 | printf STDOUT (@z); |
| 860 | print "\n"; |
| 861 | |
| 862 | # perl4 prints: foobar |
| 863 | # perl5 prints: foobar |
| 864 | |
| 865 | Probably a bug. |
| 866 | |
| 867 | =back |
| 868 | |
| 869 | =head2 Precedence Traps |
| 870 | |
| 871 | Perl4-to-Perl5 traps involving precedence order. |
| 872 | |
| 873 | =over 5 |
| 874 | |
| 875 | =item * Precedence |
| 876 | |
| 877 | LHS vs. RHS when both sides are getting an op. |
| 878 | |
| 879 | @arr = ( 'left', 'right' ); |
| 880 | $a{shift @arr} = shift @arr; |
| 881 | print join( ' ', keys %a ); |
| 882 | |
| 883 | # perl4 prints: left |
| 884 | # perl5 prints: right |
| 885 | |
| 886 | =item * Precedence |
| 887 | |
| 888 | These are now semantic errors because of precedence: |
| 889 | |
| 890 | @list = (1,2,3,4,5); |
| 891 | %map = ("a",1,"b",2,"c",3,"d",4); |
| 892 | $n = shift @list + 2; # first item in list plus 2 |
| 893 | print "n is $n, "; |
| 894 | $m = keys %map + 2; # number of items in hash plus 2 |
| 895 | print "m is $m\n"; |
| 896 | |
| 897 | # perl4 prints: n is 3, m is 6 |
| 898 | # perl5 errors and fails to compile |
| 899 | |
| 900 | =item * Precedence |
| 901 | |
| 902 | The precedence of assignment operators is now the same as the precedence |
| 903 | of assignment. Perl 4 mistakenly gave them the precedence of the associated |
| 904 | operator. So you now must parenthesize them in expressions like |
| 905 | |
| 906 | /foo/ ? ($a += 2) : ($a -= 2); |
| 907 | |
| 908 | Otherwise |
| 909 | |
| 910 | /foo/ ? $a += 2 : $a -= 2 |
| 911 | |
| 912 | would be erroneously parsed as |
| 913 | |
| 914 | (/foo/ ? $a += 2 : $a) -= 2; |
| 915 | |
| 916 | On the other hand, |
| 917 | |
| 918 | $a += /foo/ ? 1 : 2; |
| 919 | |
| 920 | now works as a C programmer would expect. |
| 921 | |
| 922 | =item * Precedence |
| 923 | |
| 924 | open FOO || die; |
| 925 | |
| 926 | is now incorrect. You need parens around the filehandle. |
| 927 | Otherwise, perl5 leaves the statement as it's default precedence: |
| 928 | |
| 929 | open(FOO || die); |
| 930 | |
| 931 | # perl4 opens or dies |
| 932 | # perl5 errors: Precedence problem: open FOO should be open(FOO) |
| 933 | |
| 934 | =item * Precedence |
| 935 | |
| 936 | perl4 gives the special variable, C<$:> precedence, where perl5 |
| 937 | treats C<$::> as main C<package> |
| 938 | |
| 939 | $a = "x"; print "$::a"; |
| 940 | |
| 941 | # perl 4 prints: -:a |
| 942 | # perl 5 prints: x |
| 943 | |
| 944 | =item * Precedence |
| 945 | |
| 946 | concatenation precedence over filetest operator? |
| 947 | |
| 948 | -e $foo .= "q" |
| 949 | |
| 950 | # perl4 prints: no output |
| 951 | # perl5 prints: Can't modify -e in concatenation |
| 952 | |
| 953 | =item * Precedence |
| 954 | |
| 955 | Assignment to value takes precedence over assignment to key in |
| 956 | perl5 when using the shift operator on both sides. |
| 957 | |
| 958 | @arr = ( 'left', 'right' ); |
| 959 | $a{shift @arr} = shift @arr; |
| 960 | print join( ' ', keys %a ); |
| 961 | |
| 962 | # perl4 prints: left |
| 963 | # perl5 prints: right |
| 964 | |
| 965 | =back |
| 966 | |
| 967 | =head2 General Regular Expression Traps using s///, etc. |
| 968 | |
| 969 | All types of RE traps. |
| 970 | |
| 971 | =over 5 |
| 972 | |
| 973 | =item * Regular Expression |
| 974 | |
| 975 | C<s'$lhs'$rhs'> now does no interpolation on either side. It used to |
| 976 | interpolate C<$lhs> but not C<$rhs>. (And still does not match a literal |
| 977 | '$' in string) |
| 978 | |
| 979 | $a=1;$b=2; |
| 980 | $string = '1 2 $a $b'; |
| 981 | $string =~ s'$a'$b'; |
| 982 | print $string,"\n"; |
| 983 | |
| 984 | # perl4 prints: $b 2 $a $b |
| 985 | # perl5 prints: 1 2 $a $b |
| 986 | |
| 987 | =item * Regular Expression |
| 988 | |
| 989 | C<m//g> now attaches its state to the searched string rather than the |
| 990 | regular expression. (Once the scope of a block is left for the sub, the |
| 991 | state of the searched string is lost) |
| 992 | |
| 993 | $_ = "ababab"; |
| 994 | while(m/ab/g){ |
| 995 | &doit("blah"); |
| 996 | } |
| 997 | sub doit{local($_) = shift; print "Got $_ "} |
| 998 | |
| 999 | # perl4 prints: blah blah blah |
| 1000 | # perl5 prints: infinite loop blah... |
| 1001 | |
| 1002 | =item * Regular Expression |
| 1003 | |
| 1004 | If no parentheses are used in a match, Perl4 sets C<$+> to |
| 1005 | the whole match, just like C<$&>. Perl5 does not. |
| 1006 | |
| 1007 | "abcdef" =~ /b.*e/; |
| 1008 | print "\$+ = $+\n"; |
| 1009 | |
| 1010 | # perl4 prints: bcde |
| 1011 | # perl5 prints: |
| 1012 | |
| 1013 | =item * Regular Expression |
| 1014 | |
| 1015 | substitution now returns the null string if it fails |
| 1016 | |
| 1017 | $string = "test"; |
| 1018 | $value = ($string =~ s/foo//); |
| 1019 | print $value, "\n"; |
| 1020 | |
| 1021 | # perl4 prints: 0 |
| 1022 | # perl5 prints: |
| 1023 | |
| 1024 | Also see L<Numerical Traps> for another example of this new feature. |
| 1025 | |
| 1026 | =item * Regular Expression |
| 1027 | |
| 1028 | C<s`lhs`rhs`> (using backticks) is now a normal substitution, with no |
| 1029 | backtick expansion |
| 1030 | |
| 1031 | $string = ""; |
| 1032 | $string =~ s`^`hostname`; |
| 1033 | print $string, "\n"; |
| 1034 | |
| 1035 | # perl4 prints: <the local hostname> |
| 1036 | # perl5 prints: hostname |
| 1037 | |
| 1038 | =item * Regular Expression |
| 1039 | |
| 1040 | Stricter parsing of variables used in regular expressions |
| 1041 | |
| 1042 | s/^([^$grpc]*$grpc[$opt$plus$rep]?)//o; |
| 1043 | |
| 1044 | # perl4: compiles w/o error |
| 1045 | # perl5: with Scalar found where operator expected ..., near "$opt$plus" |
| 1046 | |
| 1047 | an added component of this example, apparently from the same script, is |
| 1048 | the actual value of the s'd string after the substitution. |
| 1049 | C<[$opt]> is a character class in perl4 and an array subscript in perl5 |
| 1050 | |
| 1051 | $grpc = 'a'; |
| 1052 | $opt = 'r'; |
| 1053 | $_ = 'bar'; |
| 1054 | s/^([^$grpc]*$grpc[$opt]?)/foo/; |
| 1055 | print ; |
| 1056 | |
| 1057 | # perl4 prints: foo |
| 1058 | # perl5 prints: foobar |
| 1059 | |
| 1060 | =item * Regular Expression |
| 1061 | |
| 1062 | Under perl5, C<m?x?> matches only once, like C<?x?>. Under perl4, it matched |
| 1063 | repeatedly, like C</x/> or C<m!x!>. |
| 1064 | |
| 1065 | $test = "once"; |
| 1066 | sub match { $test =~ m?once?; } |
| 1067 | &match(); |
| 1068 | if( &match() ) { |
| 1069 | # m?x? matches more then once |
| 1070 | print "perl4\n"; |
| 1071 | } else { |
| 1072 | # m?x? matches only once |
| 1073 | print "perl5\n"; |
| 1074 | } |
| 1075 | |
| 1076 | # perl4 prints: perl4 |
| 1077 | # perl5 prints: perl5 |
| 1078 | |
| 1079 | |
| 1080 | =back |
| 1081 | |
| 1082 | =head2 Subroutine, Signal, Sorting Traps |
| 1083 | |
| 1084 | The general group of Perl4-to-Perl5 traps having to do with |
| 1085 | Signals, Sorting, and their related subroutines, as well as |
| 1086 | general subroutine traps. Includes some OS-Specific traps. |
| 1087 | |
| 1088 | =over 5 |
| 1089 | |
| 1090 | =item * (Signals) |
| 1091 | |
| 1092 | Barewords that used to look like strings to Perl will now look like subroutine |
| 1093 | calls if a subroutine by that name is defined before the compiler sees them. |
| 1094 | |
| 1095 | sub SeeYa { warn"Hasta la vista, baby!" } |
| 1096 | $SIG{'TERM'} = SeeYa; |
| 1097 | print "SIGTERM is now $SIG{'TERM'}\n"; |
| 1098 | |
| 1099 | # perl4 prints: SIGTERM is main'SeeYa |
| 1100 | # perl5 prints: SIGTERM is now main::1 |
| 1101 | |
| 1102 | Use B<-w> to catch this one |
| 1103 | |
| 1104 | =item * (Sort Subroutine) |
| 1105 | |
| 1106 | reverse is no longer allowed as the name of a sort subroutine. |
| 1107 | |
| 1108 | sub reverse{ print "yup "; $a <=> $b } |
| 1109 | print sort reverse a,b,c; |
| 1110 | |
| 1111 | # perl4 prints: yup yup yup yup abc |
| 1112 | # perl5 prints: abc |
| 1113 | |
| 1114 | =item * warn() specifically implies STDERR |
| 1115 | |
| 1116 | warn STDERR "Foo!"; |
| 1117 | |
| 1118 | # perl4 prints: Foo! |
| 1119 | # perl5 prints: String found where operator expected |
| 1120 | |
| 1121 | =back |
| 1122 | |
| 1123 | =head2 OS Traps |
| 1124 | |
| 1125 | =over 5 |
| 1126 | |
| 1127 | =item * (SysV) |
| 1128 | |
| 1129 | Under HPUX, and some other SysV OS's, one had to reset any signal handler, |
| 1130 | within the signal handler function, each time a signal was handled with |
| 1131 | perl4. With perl5, the reset is now done correctly. Any code relying |
| 1132 | on the handler _not_ being reset will have to be reworked. |
| 1133 | |
| 1134 | 5.002 and beyond uses sigaction() under SysV |
| 1135 | |
| 1136 | sub gotit { |
| 1137 | print "Got @_... "; |
| 1138 | } |
| 1139 | $SIG{'INT'} = 'gotit'; |
| 1140 | |
| 1141 | $| = 1; |
| 1142 | $pid = fork; |
| 1143 | if ($pid) { |
| 1144 | kill('INT', $pid); |
| 1145 | sleep(1); |
| 1146 | kill('INT', $pid); |
| 1147 | } else { |
| 1148 | while (1) {sleep(10);} |
| 1149 | } |
| 1150 | |
| 1151 | # perl4 (HPUX) prints: Got INT... |
| 1152 | # perl5 (HPUX) prints: Got INT... Got INT... |
| 1153 | |
| 1154 | =item * (SysV) |
| 1155 | |
| 1156 | Under SysV OS's, C<seek()> on a file opened to append C<E<gt>E<gt>> now does |
| 1157 | the right thing w.r.t. the fopen() man page. e.g. - When a file is opened |
| 1158 | for append, it is impossible to overwrite information already in |
| 1159 | the file. |
| 1160 | |
| 1161 | open(TEST,">>seek.test"); |
| 1162 | $start = tell TEST ; |
| 1163 | foreach(1 .. 9){ |
| 1164 | print TEST "$_ "; |
| 1165 | } |
| 1166 | $end = tell TEST ; |
| 1167 | seek(TEST,$start,0); |
| 1168 | print TEST "18 characters here"; |
| 1169 | |
| 1170 | # perl4 (solaris) seek.test has: 18 characters here |
| 1171 | # perl5 (solaris) seek.test has: 1 2 3 4 5 6 7 8 9 18 characters here |
| 1172 | |
| 1173 | |
| 1174 | |
| 1175 | =back |
| 1176 | |
| 1177 | =head2 Interpolation Traps |
| 1178 | |
| 1179 | =over 5 |
| 1180 | |
| 1181 | =item * Interpolation |
| 1182 | |
| 1183 | @ now always interpolates an array in double-quotish strings. |
| 1184 | |
| 1185 | print "To: someone@somewhere.com\n"; |
| 1186 | |
| 1187 | # perl4 prints: To:someone@somewhere.com |
| 1188 | # perl5 errors : Literal @somewhere now requires backslash |
| 1189 | |
| 1190 | =item * Interpolation |
| 1191 | |
| 1192 | Perl4-to-Perl5 traps having to do with how things get interpolated |
| 1193 | within certain expressions, statements, contexts, or whatever. |
| 1194 | |
| 1195 | Double-quoted strings may no longer end with an unescaped $ or @. |
| 1196 | |
| 1197 | $foo = "foo$"; |
| 1198 | $bar = "bar@"; |
| 1199 | print "foo is $foo, bar is $bar\n"; |
| 1200 | |
| 1201 | # perl4 prints: foo is foo$, bar is bar@ |
| 1202 | # perl5 errors: Final $ should be \$ or $name |
| 1203 | |
| 1204 | Note: perl5 DOES NOT error on the terminating @ in $bar |
| 1205 | |
| 1206 | =item * Interpolation |
| 1207 | |
| 1208 | The construct "this is $$x" used to interpolate the pid at that |
| 1209 | point, but now apparently tries to dereference C<$x>. C<$$> by itself still |
| 1210 | works fine, however. |
| 1211 | |
| 1212 | print "this is $$x\n"; |
| 1213 | |
| 1214 | # perl4 prints: this is XXXx (XXX is the current pid) |
| 1215 | # perl5 prints: this is |
| 1216 | |
| 1217 | =item * Interpolation |
| 1218 | |
| 1219 | Creation of hashes on the fly with C<eval "EXPR"> now requires either both |
| 1220 | C<$>'s to be protected in the specification of the hash name, or both curlies |
| 1221 | to be protected. If both curlies are protected, the result will be compatible |
| 1222 | with perl4 and perl5. This is a very common practice, and should be changed |
| 1223 | to use the block form of C<eval{}> if possible. |
| 1224 | |
| 1225 | $hashname = "foobar"; |
| 1226 | $key = "baz"; |
| 1227 | $value = 1234; |
| 1228 | eval "\$$hashname{'$key'} = q|$value|"; |
| 1229 | (defined($foobar{'baz'})) ? (print "Yup") : (print "Nope"); |
| 1230 | |
| 1231 | # perl4 prints: Yup |
| 1232 | # perl5 prints: Nope |
| 1233 | |
| 1234 | Changing |
| 1235 | |
| 1236 | eval "\$$hashname{'$key'} = q|$value|"; |
| 1237 | |
| 1238 | to |
| 1239 | |
| 1240 | eval "\$\$hashname{'$key'} = q|$value|"; |
| 1241 | |
| 1242 | causes the following result: |
| 1243 | |
| 1244 | # perl4 prints: Nope |
| 1245 | # perl5 prints: Yup |
| 1246 | |
| 1247 | or, changing to |
| 1248 | |
| 1249 | eval "\$$hashname\{'$key'\} = q|$value|"; |
| 1250 | |
| 1251 | causes the following result: |
| 1252 | |
| 1253 | # perl4 prints: Yup |
| 1254 | # perl5 prints: Yup |
| 1255 | # and is compatible for both versions |
| 1256 | |
| 1257 | |
| 1258 | =item * Interpolation |
| 1259 | |
| 1260 | perl4 programs which unconsciously rely on the bugs in earlier perl versions. |
| 1261 | |
| 1262 | perl -e '$bar=q/not/; print "This is $foo{$bar} perl5"' |
| 1263 | |
| 1264 | # perl4 prints: This is not perl5 |
| 1265 | # perl5 prints: This is perl5 |
| 1266 | |
| 1267 | =item * Interpolation |
| 1268 | |
| 1269 | You also have to be careful about array references. |
| 1270 | |
| 1271 | print "$foo{" |
| 1272 | |
| 1273 | perl 4 prints: { |
| 1274 | perl 5 prints: syntax error |
| 1275 | |
| 1276 | =item * Interpolation |
| 1277 | |
| 1278 | Similarly, watch out for: |
| 1279 | |
| 1280 | $foo = "array"; |
| 1281 | print "\$$foo{bar}\n"; |
| 1282 | |
| 1283 | # perl4 prints: $array{bar} |
| 1284 | # perl5 prints: $ |
| 1285 | |
| 1286 | Perl 5 is looking for C<$array{bar}> which doesn't exist, but perl 4 is |
| 1287 | happy just to expand $foo to "array" by itself. Watch out for this |
| 1288 | especially in C<eval>'s. |
| 1289 | |
| 1290 | =item * Interpolation |
| 1291 | |
| 1292 | C<qq()> string passed to C<eval> |
| 1293 | |
| 1294 | eval qq( |
| 1295 | foreach \$y (keys %\$x\) { |
| 1296 | \$count++; |
| 1297 | } |
| 1298 | ); |
| 1299 | |
| 1300 | # perl4 runs this ok |
| 1301 | # perl5 prints: Can't find string terminator ")" |
| 1302 | |
| 1303 | =back |
| 1304 | |
| 1305 | =head2 DBM Traps |
| 1306 | |
| 1307 | General DBM traps. |
| 1308 | |
| 1309 | =over 5 |
| 1310 | |
| 1311 | =item * DBM |
| 1312 | |
| 1313 | Existing dbm databases created under perl4 (or any other dbm/ndbm tool) |
| 1314 | may cause the same script, run under perl5, to fail. The build of perl5 |
| 1315 | must have been linked with the same dbm/ndbm as the default for C<dbmopen()> |
| 1316 | to function properly without C<tie>'ing to an extension dbm implementation. |
| 1317 | |
| 1318 | dbmopen (%dbm, "file", undef); |
| 1319 | print "ok\n"; |
| 1320 | |
| 1321 | # perl4 prints: ok |
| 1322 | # perl5 prints: ok (IFF linked with -ldbm or -lndbm) |
| 1323 | |
| 1324 | |
| 1325 | =item * DBM |
| 1326 | |
| 1327 | Existing dbm databases created under perl4 (or any other dbm/ndbm tool) |
| 1328 | may cause the same script, run under perl5, to fail. The error generated |
| 1329 | when exceeding the limit on the key/value size will cause perl5 to exit |
| 1330 | immediately. |
| 1331 | |
| 1332 | dbmopen(DB, "testdb",0600) || die "couldn't open db! $!"; |
| 1333 | $DB{'trap'} = "x" x 1024; # value too large for most dbm/ndbm |
| 1334 | print "YUP\n"; |
| 1335 | |
| 1336 | # perl4 prints: |
| 1337 | dbm store returned -1, errno 28, key "trap" at - line 3. |
| 1338 | YUP |
| 1339 | |
| 1340 | # perl5 prints: |
| 1341 | dbm store returned -1, errno 28, key "trap" at - line 3. |
| 1342 | |
| 1343 | =back |
| 1344 | |
| 1345 | =head2 Unclassified Traps |
| 1346 | |
| 1347 | Everything else. |
| 1348 | |
| 1349 | =over 5 |
| 1350 | |
| 1351 | =item * Unclassified |
| 1352 | |
| 1353 | C<require>/C<do> trap using returned value |
| 1354 | |
| 1355 | If the file doit.pl has: |
| 1356 | |
| 1357 | sub foo { |
| 1358 | $rc = do "./do.pl"; |
| 1359 | return 8; |
| 1360 | } |
| 1361 | print &foo, "\n"; |
| 1362 | |
| 1363 | And the do.pl file has the following single line: |
| 1364 | |
| 1365 | return 3; |
| 1366 | |
| 1367 | Running doit.pl gives the following: |
| 1368 | |
| 1369 | # perl 4 prints: 3 (aborts the subroutine early) |
| 1370 | # perl 5 prints: 8 |
| 1371 | |
| 1372 | Same behavior if you replace C<do> with C<require>. |
| 1373 | |
| 1374 | =back |
| 1375 | |
| 1376 | As always, if any of these are ever officially declared as bugs, |
| 1377 | they'll be fixed and removed. |
| 1378 | |