3 perltrap - Perl traps for the unwary
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>.
13 Accustomed B<awk> users should take special note of the following:
19 The English module, loaded via
23 allows you to refer to special variables (like $RS) as
24 though they were in B<awk>; see L<perlvar> for details.
28 Semicolons are required after all simple statements in Perl (except
29 at the end of a block). Newline is not a statement delimiter.
33 Curly brackets are required on C<if>s and C<while>s.
37 Variables begin with "$" or "@" in Perl.
41 Arrays index from 0. Likewise string positions in substr() and
46 You have to decide whether your array has numeric or string indices.
50 Associative array values do not spring into existence upon mere
55 You have to decide whether you want to use string or numeric
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
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>.
72 $<I<digit>> does not refer to fields--it refers to substrings matched by
73 the last match pattern.
77 The print() statement does not add field and record separators unless
78 you set C<$,> and C<$.>. You can set $OFS and $ORS if you're using
83 You must open your files before you print to them.
87 The range operator is "..", not comma. The comma operator works as in
92 The match operator is "=~", not "~". ("~" is the one's complement
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.)
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.)
111 The C<next>, C<exit>, and C<continue> keywords work differently.
116 The following variables work differently:
119 ARGC $#ARGV or scalar @ARGV
123 FS (whatever you like)
124 NF $#Fld, or some such
136 You cannot set $RS to a pattern, only a string.
140 When in doubt, run the B<awk> construct through B<a2p> and see what it
147 Cerebral C programmers should take note of the following:
153 Curly brackets are required on C<if>'s and C<while>'s.
157 You must use C<elsif> rather than C<else if>.
161 The C<break> and C<continue> keywords from C become in
162 Perl C<last> and C<next>, respectively.
163 Unlike in C, these do I<NOT> work within a C<do { } while> construct.
167 There's no switch statement. (But it's easy to build one on the fly.)
171 Variables begin with "$" or "@" in Perl.
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.
181 Comments begin with "#", not "/*".
185 You can't take the address of anything, although a similar operator
186 in Perl 5 is the backslash, which creates a reference.
190 C<ARGV> must be capitalized. C<$ARGV[0]> is C's C<argv[1]>, and C<argv[0]>
195 System calls such as link(), unlink(), rename(), etc. return nonzero for
200 Signal handlers deal with signal names, not numbers. Use C<kill -l>
201 to find their names on your system.
207 Seasoned B<sed> programmers should take note of the following:
213 Backreferences in substitutions use "$" rather than "\".
217 The pattern matching metacharacters "(", ")", and "|" do not have backslashes
222 The range operator is C<...>, rather than comma.
228 Sharp shell programmers should take note of the following:
234 The backtick operator does variable interpolation without regard to
235 the presence of single quotes in the command.
239 The backtick operator does no translation of the return value, unlike B<csh>.
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.
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).
255 The arguments are available via @ARGV, not $1, $2, etc.
259 The environment is not automatically made available as separate scalar
266 Practicing Perl Programmers should take note of the following:
272 Remember that many operations behave differently in a list
273 context than they do in a scalar one. See L<perldata> for details.
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.
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>.
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.
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 $_ if the
300 file read is the sole condition in a while loop:
303 while ($_ = <FH>) { }..
304 <FH>; # data discarded!
308 Remember not to use "C<=>" when you need "C<=~>";
309 these two constructs are quite different:
316 The C<do {}> construct isn't a real loop that you can use
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
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.
335 =head2 Perl4 to Perl5 Traps
337 Practicing Perl4 Programmers should take note of the following
338 Perl4-to-Perl5 specific traps.
340 They're crudely ordered according to the following list:
344 =item Discontinuance, Deprecation, and BugFix traps
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.
352 Traps that appear to stem from the new parser.
354 =item Numerical Traps
356 Traps having to do with numerical or mathematical operators.
358 =item General data type traps
360 Traps involving perl standard data types.
362 =item Context Traps - scalar, list contexts
364 Traps related to context within lists, scalar statements/declarations.
366 =item Precedence Traps
368 Traps related to the precedence of parsing, evaluation, and execution of
371 =item General Regular Expression Traps using s///, etc.
373 Traps related to the use of pattern matching.
375 =item Subroutine, Signal, Sorting Traps
377 Traps related to the use of signals and signal handlers, general subroutines,
378 and sorting, along with sorting subroutines.
386 Traps specific to the use of C<dbmopen()>, and specific dbm implementations.
388 =item Unclassified Traps
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>.
398 =head2 Discontinuance, Deprecation, and BugFix traps
400 Anything that has been discontinued, deprecated, or fixed as
405 =item * Discontinuance
407 Symbols starting with "_" are no longer forced into package main, except
408 for C<$_> itself (and C<@_>, etc.).
414 print "\$_legacy is ",$_legacy,"\n";
416 # perl4 prints: $_legacy is 1
417 # perl5 prints: $_legacy is
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.
424 $a=1;$b=2;$c=3;$var=4;
426 print "$var::abc::xyz\n";
428 # perl4 prints: 1::2::3 4::abc::xyz
431 Given that C<::> is now the preferred package delimiter, it is debatable
432 whether this should be classed as a bug or not.
433 (The older package delimiter, ' ,is used here)
439 # perl5 prints: Can't find string terminator "'" anywhere before EOF
441 Also see precedence traps, for parsing C<$:>.
445 The second and third arguments of C<splice()> are now evaluated in scalar
446 context (as the Camel says) rather than list context.
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";
455 # perl5 prints: c d e
457 =item * Discontinuance
459 You can't do a C<goto> into a block that is optimized away. Darn.
465 print "Here I is!\n";
468 # perl4 prints: Here I is!
469 # perl5 dumps core (SEGV)
471 =item * Discontinuance
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.
479 print "a is $a, b is $b\n";
481 # perl4 prints: a is foo bar, b is baz
482 # perl5 errors: Bare word found where operator expected
484 =item * Discontinuance
486 The archaic while/if BLOCK BLOCK syntax is no longer supported.
495 # perl4 prints: True!
496 # perl5 errors: syntax error at test.pl line 1, near "if {"
500 The C<**> operator now binds more tightly than unary minus.
501 It was documented to work this way before, but didn't.
508 =item * Discontinuance
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
517 @list = ('ab','abc','bcd','def');
518 foreach $var (grep(/ab/,@list)){
521 print (join(':',@list));
523 # perl4 prints: ab:abc:bcd:def
524 # perl5 prints: 1:1:bcd:def
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
530 foreach $var (grep(/ab/,@list)){
534 foreach $var (@tmp = grep(/ab/,@list)){
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<$_>.)
542 Some error messages will be different.
544 =item * Discontinuance
546 Some bugs may have been inadvertently removed. :-)
552 Perl4-to-Perl5 traps from having to do with parsing.
558 Note the space between . and =
560 $string . = "more string";
563 # perl4 prints: more string
564 # perl5 prints: syntax error at - line 1, near ". ="
568 Better parsing in perl 5
572 print("hello, world\n");
574 # perl4 prints: hello, world
575 # perl5 prints: syntax error
579 "if it looks like a function, it is a function" rule.
582 ($foo == 1) ? "is one\n" : "is zero\n";
584 # perl4 prints: is zero
585 # perl5 warns: "Useless use of a constant in void context" if using -w
589 =head2 Numerical Traps
591 Perl4-to-Perl5 traps having to do with numerical operators,
592 operands, or output from same.
598 Formatted output and significant digits
600 print 7.373504 - 0, "\n";
601 printf "%20.18f\n", 7.373504 - 0;
613 Large integer trap with autoincrement
615 $a = $b = 2147483647;
622 2147483647 2147483647
623 2147483648 2147483648
626 2147483647 2147483647
627 2147483648 -2147483648
631 Assignment of return values from numeric equality tests
632 does not work in perl5 when the test evaluates to false (0).
633 Logical tests now return an null, instead of 0
641 Also see the L<General Regular Expression Traps> tests for another example
642 of this new feature...
646 =head2 General data type traps
648 Perl4-to-Perl5 traps involving most data-types, and their usage
649 within certain expressions and/or context.
655 Negative array subscripts now count from the end of the array.
657 @a = (1, 2, 3, 4, 5);
658 print "The third element of the array is $a[3] also expressed as $a[-2] \n";
660 # perl4 prints: The third element of the array is 4 also expressed as
661 # perl5 prints: The third element of the array is 4 also expressed as 4
665 Setting C<$#array> lower now discards array elements, and makes them
666 impossible to recover.
669 print "Before: ",join('',@a);
671 print ", After: ",join('',@a);
673 print ", Recovered: ",join('',@a),"\n";
675 # perl4 prints: Before: abcde, After: ab, Recovered: abcd
676 # perl5 prints: Before: abcde, After: ab, Recovered: ab
680 Hashes get defined before use
683 die "scalar \$s defined" if defined($s);
684 die "array \@a defined" if defined(@a);
685 die "hash \%h defined" if defined(%h);
688 # perl5 dies: hash %h defined
692 glob assignment from variable to variable will fail if the assigned
693 variable is localized subsequent to the assignment
695 @a = ("This is Perl 4");
700 # perl4 prints: This is Perl 4
705 *fred = *barney; # fred is aliased to barney
708 print "@fred"; # should print "1, 2, 4"
710 # perl4 prints: 1 2 4
711 # perl5 prints: Literal @fred now requires backslash
713 =item * (Scalar String)
715 Changes in unary negation (of strings)
716 This change effects both the return value and what it
717 does to auto(magic)increment.
724 # perl4 prints: aab : -0 : 1
725 # perl5 prints: aab : -aab : aac
729 perl 4 lets you modify constants:
733 for ($x = 0; $x < 3; $x++) {
737 print "before: $_[0]";
739 print " after: $_[0]\n";
750 # Modification of a read-only value attempted at foo.pl line 12.
755 The behavior is slightly different for:
757 print "$x", defined $x
760 # perl 5: <no output, $x is not called into existence>
762 =item * (Variable Suicide)
764 Variable suicide behavior is more consistent under Perl 5.
765 Perl5 exhibits the same behavior for associative arrays and scalars,
766 that perl4 exhibits only for scalars.
768 $aGlobal{ "aKey" } = "global value";
769 print "MAIN:", $aGlobal{"aKey"}, "\n";
774 local( *theArgument ) = @_;
775 local( %aNewLocal ); # perl 4 != 5.001l,m
776 $aNewLocal{"aKey"} = "this should never appear";
777 print "SUB: ", $theArgument{"aKey"}, "\n";
778 $aNewLocal{"aKey"} = "level $GlobalLevel"; # what should print
780 if( $GlobalLevel<4 ) {
795 # SUB: this should never appear
796 # SUB: this should never appear
797 # SUB: this should never appear
801 =head2 Context Traps - scalar, list contexts
805 =item * (list context)
807 The elements of argument lists for formats are now evaluated in list
808 context. This means you can interpolate list values now.
810 @fmt = ("foo","bar","baz");
817 # perl4 errors: Please use commas to separate fields in file
818 # perl5 prints: foo bar baz
820 =item * (scalar context)
822 The C<caller()> function now returns a false value in a scalar context
823 if there is no caller. This lets library files determine if they're
826 caller() ? (print "You rang?\n") : (print "Got a 0\n");
828 # perl4 errors: There is no caller
829 # perl5 prints: Got a 0
831 =item * (scalar context)
833 The comma operator in a scalar context is now guaranteed to give a
834 scalar context to its arguments.
840 # Perl4 prints: x = c # Thinks list context interpolates list
841 # Perl5 prints: x = 3 # Knows scalar uses length of list
843 =item * (list, builtin)
845 C<sprintf()> funkiness (array argument converted to scalar array count)
846 This test could be added to t/op/sprintf.t
848 @z = ('%s%s', 'foo', 'bar');
850 if ($x eq 'foobar') {print "ok 2\n";} else {print "not ok 2 '$x'\n";}
853 # perl5 prints: not ok 2
855 C<printf()> works fine, though:
860 # perl4 prints: foobar
861 # perl5 prints: foobar
867 =head2 Precedence Traps
869 Perl4-to-Perl5 traps involving precedence order.
873 These are now semantic errors because of precedence:
876 %map = ("a",1,"b",2,"c",3,"d",4);
877 $n = shift @list + 2; # first item in list plus 2
879 $m = keys %map + 2; # number of items in hash plus 2
882 # perl4 prints: n is 3, m is 6
883 # perl5 errors and fails to compile
887 The precedence of assignment operators is now the same as the precedence
888 of assignment. Perl 4 mistakenly gave them the precedence of the associated
889 operator. So you now must parenthesize them in expressions like
891 /foo/ ? ($a += 2) : ($a -= 2);
895 /foo/ ? $a += 2 : $a -= 2
897 would be erroneously parsed as
899 (/foo/ ? $a += 2 : $a) -= 2;
905 now works as a C programmer would expect.
911 is now incorrect. You need parens around the filehandle.
912 Otherwise, perl5 leaves the statement as it's default precedence:
916 # perl4 opens or dies
917 # perl5 errors: Precedence problem: open FOO should be open(FOO)
921 perl4 gives the special variable, C<$:> precedence, where perl5
922 treats C<$::> as main C<package>
924 $a = "x"; print "$::a";
931 concatenation precedence over filetest operator?
935 # perl4 prints: no output
936 # perl5 prints: Can't modify -e in concatenation
940 Assignment to value takes precedence over assignment to key in
941 perl5 when using the shift operator on both sides.
943 @arr = ( 'left', 'right' );
944 $a{shift @arr} = shift @arr;
945 print join( ' ', keys %a );
948 # perl5 prints: right
952 =head2 General Regular Expression Traps using s///, etc.
954 All types of RE traps.
958 =item * Regular Expression
960 C<s'$lhs'$rhs'> now does no interpolation on either side. It used to
961 interpolate C<$lhs> but not C<$rhs>. (And still does not match a literal
965 $string = '1 2 $a $b';
969 # perl4 prints: $b 2 $a $b
970 # perl5 prints: 1 2 $a $b
972 =item * Regular Expression
974 C<m//g> now attaches its state to the searched string rather than the
975 regular expression. (Once the scope of a block is left for the sub, the
976 state of the searched string is lost)
982 sub doit{local($_) = shift; print "Got $_ "}
984 # perl4 prints: blah blah blah
985 # perl5 prints: infinite loop blah...
987 =item * Regular Expression
989 If no parentheses are used in a match, Perl4 sets C<$+> to
990 the whole match, just like C<$&>. Perl5 does not.
998 =item * Regular Expression
1000 substitution now returns the null string if it fails
1003 $value = ($string =~ s/foo//);
1009 Also see L<Numerical Traps> for another example of this new feature.
1011 =item * Regular Expression
1013 C<s`lhs`rhs`> (using backticks) is now a normal substitution, with no
1017 $string =~ s`^`hostname`;
1018 print $string, "\n";
1020 # perl4 prints: <the local hostname>
1021 # perl5 prints: hostname
1023 =item * Regular Expression
1025 Stricter parsing of variables used in regular expressions
1027 s/^([^$grpc]*$grpc[$opt$plus$rep]?)//o;
1029 # perl4: compiles w/o error
1030 # perl5: with Scalar found where operator expected ..., near "$opt$plus"
1032 an added component of this example, apparently from the same script, is
1033 the actual value of the s'd string after the substitution.
1034 C<[$opt]> is a character class in perl4 and an array subscript in perl5
1039 s/^([^$grpc]*$grpc[$opt]?)/foo/;
1043 # perl5 prints: foobar
1045 =item * Regular Expression
1047 Under perl5, C<m?x?> matches only once, like C<?x?>. Under perl4, it matched
1048 repeatedly, like C</x/> or C<m!x!>.
1051 sub match { $test =~ m?once?; }
1054 # m?x? matches more then once
1057 # m?x? matches only once
1061 # perl4 prints: perl4
1062 # perl5 prints: perl5
1067 =head2 Subroutine, Signal, Sorting Traps
1069 The general group of Perl4-to-Perl5 traps having to do with
1070 Signals, Sorting, and their related subroutines, as well as
1071 general subroutine traps. Includes some OS-Specific traps.
1077 Barewords that used to look like strings to Perl will now look like subroutine
1078 calls if a subroutine by that name is defined before the compiler sees them.
1080 sub SeeYa { warn"Hasta la vista, baby!" }
1081 $SIG{'TERM'} = SeeYa;
1082 print "SIGTERM is now $SIG{'TERM'}\n";
1084 # perl4 prints: SIGTERM is main'SeeYa
1085 # perl5 prints: SIGTERM is now main::1
1087 Use B<-w> to catch this one
1089 =item * (Sort Subroutine)
1091 reverse is no longer allowed as the name of a sort subroutine.
1093 sub reverse{ print "yup "; $a <=> $b }
1094 print sort reverse a,b,c;
1096 # perl4 prints: yup yup yup yup abc
1107 Under HPUX, and some other SysV OS's, one had to reset any signal handler,
1108 within the signal handler function, each time a signal was handled with
1109 perl4. With perl5, the reset is now done correctly. Any code relying
1110 on the handler _not_ being reset will have to be reworked.
1112 5.002 and beyond uses sigaction() under SysV
1117 $SIG{'INT'} = 'gotit';
1126 while (1) {sleep(10);}
1129 # perl4 (HPUX) prints: Got INT...
1130 # perl5 (HPUX) prints: Got INT... Got INT...
1134 Under SysV OS's, C<seek()> on a file opened to append C<E<gt>E<gt>> now does
1135 the right thing w.r.t. the fopen() man page. e.g. - When a file is opened
1136 for append, it is impossible to overwrite information already in
1139 open(TEST,">>seek.test");
1140 $start = tell TEST ;
1145 seek(TEST,$start,0);
1146 print TEST "18 characters here";
1148 # perl4 (solaris) seek.test has: 18 characters here
1149 # perl5 (solaris) seek.test has: 1 2 3 4 5 6 7 8 9 18 characters here
1155 =head2 Interpolation Traps
1159 =item * Interpolation
1161 @ now always interpolates an array in double-quotish strings.
1163 print "To: someone@somewhere.com\n";
1165 # perl4 prints: To:someone@somewhere.com
1166 # perl5 errors : Literal @somewhere now requires backslash
1168 =item * Interpolation
1170 Perl4-to-Perl5 traps having to do with how things get interpolated
1171 within certain expressions, statements, contexts, or whatever.
1173 Double-quoted strings may no longer end with an unescaped $ or @.
1177 print "foo is $foo, bar is $bar\n";
1179 # perl4 prints: foo is foo$, bar is bar@
1180 # perl5 errors: Final $ should be \$ or $name
1182 Note: perl5 DOES NOT error on the terminating @ in $bar
1184 =item * Interpolation
1186 The construct "this is $$x" used to interpolate the pid at that
1187 point, but now apparently tries to dereference C<$x>. C<$$> by itself still
1188 works fine, however.
1190 print "this is $$x\n";
1192 # perl4 prints: this is XXXx (XXX is the current pid)
1193 # perl5 prints: this is
1195 =item * Interpolation
1197 Creation of hashes on the fly with C<eval "EXPR"> now requires either both
1198 C<$>'s to be protected in the specification of the hash name, or both curlies
1199 to be protected. If both curlies are protected, the result will be compatible
1200 with perl4 and perl5. This is a very common practice, and should be changed
1201 to use the block form of C<eval{}> if possible.
1203 $hashname = "foobar";
1206 eval "\$$hashname{'$key'} = q|$value|";
1207 (defined($foobar{'baz'})) ? (print "Yup") : (print "Nope");
1210 # perl5 prints: Nope
1214 eval "\$$hashname{'$key'} = q|$value|";
1218 eval "\$\$hashname{'$key'} = q|$value|";
1220 causes the following result:
1222 # perl4 prints: Nope
1227 eval "\$$hashname\{'$key'\} = q|$value|";
1229 causes the following result:
1233 # and is compatible for both versions
1236 =item * Interpolation
1238 perl4 programs which unconsciously rely on the bugs in earlier perl versions.
1240 perl -e '$bar=q/not/; print "This is $foo{$bar} perl5"'
1242 # perl4 prints: This is not perl5
1243 # perl5 prints: This is perl5
1245 =item * Interpolation
1247 You also have to be careful about array references.
1252 perl 5 prints: syntax error
1254 =item * Interpolation
1256 Similarly, watch out for:
1259 print "\$$foo{bar}\n";
1261 # perl4 prints: $array{bar}
1264 Perl 5 is looking for C<$array{bar}> which doesn't exist, but perl 4 is
1265 happy just to expand $foo to "array" by itself. Watch out for this
1266 especially in C<eval>'s.
1268 =item * Interpolation
1270 C<qq()> string passed to C<eval>
1273 foreach \$y (keys %\$x\) {
1278 # perl4 runs this ok
1279 # perl5 prints: Can't find string terminator ")"
1291 Existing dbm databases created under perl4 (or any other dbm/ndbm tool)
1292 may cause the same script, run under perl5, to fail. The build of perl5
1293 must have been linked with the same dbm/ndbm as the default for C<dbmopen()>
1294 to function properly without C<tie>'ing to an extension dbm implementation.
1296 dbmopen (%dbm, "file", undef);
1300 # perl5 prints: ok (IFF linked with -ldbm or -lndbm)
1305 Existing dbm databases created under perl4 (or any other dbm/ndbm tool)
1306 may cause the same script, run under perl5, to fail. The error generated
1307 when exceeding the limit on the key/value size will cause perl5 to exit
1310 dbmopen(DB, "testdb",0600) || die "couldn't open db! $!";
1311 $DB{'trap'} = "x" x 1024; # value too large for most dbm/ndbm
1315 dbm store returned -1, errno 28, key "trap" at - line 3.
1319 dbm store returned -1, errno 28, key "trap" at - line 3.
1323 =head2 Unclassified Traps
1327 =item * Unclassified
1329 C<require>/C<do> trap using returned value
1331 If the file doit.pl has:
1339 And the do.pl file has the following single line:
1343 Running doit.pl gives the following:
1345 # perl 4 prints: 3 (aborts the subroutine early)
1348 Same behavior if you replace C<do> with C<require>.
1352 As always, if any of these are ever officially declared as bugs,
1353 they'll be fixed and removed.