summaryrefslogtreecommitdiff
path: root/pod/perlsyn.pod
blob: 9d0c9209eaa8d220486b666a7a84e3b9226c282f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
=head1 NAME

perlsyn - Perl syntax

=head1 DESCRIPTION

A Perl script consists of a sequence of declarations and statements.
The sequence of statements is executed just once, unlike in B<sed>
and B<awk> scripts, where the sequence of statements is executed
for each input line.  While this means that you must explicitly
loop over the lines of your input file (or files), it also means
you have much more control over which files and which lines you look at.
(Actually, I'm lying--it is possible to do an implicit loop with
either the B<-n> or B<-p> switch.  It's just not the mandatory
default like it is in B<sed> and B<awk>.)

Perl is, for the most part, a free-form language.  (The only exception
to this is format declarations, for obvious reasons.)  Text from a
C<"#"> character until the end of the line is a comment, and is
ignored.  If you attempt to use C</* */> C-style comments, it will be
interpreted either as division or pattern matching, depending on the
context, and C++ C<//> comments just look like a null regular
expression, so don't do that.

=head2 Declarations

The only things you need to declare in Perl are report formats
and subroutines--and even undefined subroutines can be handled
through AUTOLOAD.  A variable holds the undefined value (C<undef>)
until it has been assigned a defined value, which is anything
other than C<undef>.  When used as a number, C<undef> is treated
as C<0>; when used as a string, it is treated the empty string,
C<"">; and when used as a reference that isn't being assigned
to, it is treated as an error.  If you enable warnings, you'll
be notified of an uninitialized value whenever you treat C<undef>
as a string or a number.  Well, usually.  Boolean ("don't-care")
contexts and operators such as C<++>, C<-->, C<+=>, C<-=>, and
C<.=> are always exempt from such warnings.

A declaration can be put anywhere a statement can, but has no effect on
the execution of the primary sequence of statements--declarations all
take effect at compile time.  Typically all the declarations are put at
the beginning or the end of the script.  However, if you're using
lexically-scoped private variables created with C<my()>, you'll
have to make sure
your format or subroutine definition is within the same block scope
as the my if you expect to be able to access those private variables.

Declaring a subroutine allows a subroutine name to be used as if it were a
list operator from that point forward in the program.  You can declare a
subroutine without defining it by saying C<sub name>, thus:

    sub myname;
    $me = myname $0 		or die "can't get myname";

Note that myname() functions as a list operator, not as a unary operator;
so be careful to use C<or> instead of C<||> in this case.  However, if
you were to declare the subroutine as C<sub myname ($)>, then
C<myname> would function as a unary operator, so either C<or> or
C<||> would work.

Subroutines declarations can also be loaded up with the C<require> statement
or both loaded and imported into your namespace with a C<use> statement.
See L<perlmod> for details on this.

A statement sequence may contain declarations of lexically-scoped
variables, but apart from declaring a variable name, the declaration acts
like an ordinary statement, and is elaborated within the sequence of
statements as if it were an ordinary statement.  That means it actually
has both compile-time and run-time effects.

=head2 Simple statements

The only kind of simple statement is an expression evaluated for its
side effects.  Every simple statement must be terminated with a
semicolon, unless it is the final statement in a block, in which case
the semicolon is optional.  (A semicolon is still encouraged there if the
block takes up more than one line, because you may eventually add another line.)
Note that there are some operators like C<eval {}> and C<do {}> that look
like compound statements, but aren't (they're just TERMs in an expression),
and thus need an explicit termination if used as the last item in a statement.

Any simple statement may optionally be followed by a I<SINGLE> modifier,
just before the terminating semicolon (or block ending).  The possible
modifiers are:

    if EXPR
    unless EXPR
    while EXPR
    until EXPR
    foreach EXPR

The C<if> and C<unless> modifiers have the expected semantics,
presuming you're a speaker of English.  The C<foreach> modifier is an
iterator:  For each value in EXPR, it aliases C<$_> to the value and
executes the statement.  The C<while> and C<until> modifiers have the
usual "C<while> loop" semantics (conditional evaluated first), except
when applied to a C<do>-BLOCK (or to the deprecated C<do>-SUBROUTINE
statement), in which case the block executes once before the
conditional is evaluated.  This is so that you can write loops like:

    do {
	$line = <STDIN>;
	...
    } until $line  eq ".\n";

See L<perlfunc/do>.  Note also that the loop control statements described
later will I<NOT> work in this construct, because modifiers don't take
loop labels.  Sorry.  You can always put another block inside of it
(for C<next>) or around it (for C<last>) to do that sort of thing.
For C<next>, just double the braces:

    do {{
	next if $x == $y;
	# do something here
    }} until $x++ > $z;

For C<last>, you have to be more elaborate:

    LOOP: { 
	    do {
		last if $x = $y**2;
		# do something here
	    } while $x++ <= $z;
    }

=head2 Compound statements

In Perl, a sequence of statements that defines a scope is called a block.
Sometimes a block is delimited by the file containing it (in the case
of a required file, or the program as a whole), and sometimes a block
is delimited by the extent of a string (in the case of an eval).

But generally, a block is delimited by curly brackets, also known as braces.
We will call this syntactic construct a BLOCK.

The following compound statements may be used to control flow:

    if (EXPR) BLOCK
    if (EXPR) BLOCK else BLOCK
    if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK
    LABEL while (EXPR) BLOCK
    LABEL while (EXPR) BLOCK continue BLOCK
    LABEL for (EXPR; EXPR; EXPR) BLOCK
    LABEL foreach VAR (LIST) BLOCK
    LABEL foreach VAR (LIST) BLOCK continue BLOCK
    LABEL BLOCK continue BLOCK

Note that, unlike C and Pascal, these are defined in terms of BLOCKs,
not statements.  This means that the curly brackets are I<required>--no
dangling statements allowed.  If you want to write conditionals without
curly brackets there are several other ways to do it.  The following
all do the same thing:

    if (!open(FOO)) { die "Can't open $FOO: $!"; }
    die "Can't open $FOO: $!" unless open(FOO);
    open(FOO) or die "Can't open $FOO: $!";	# FOO or bust!
    open(FOO) ? 'hi mom' : die "Can't open $FOO: $!";
			# a bit exotic, that last one

The C<if> statement is straightforward.  Because BLOCKs are always
bounded by curly brackets, there is never any ambiguity about which
C<if> an C<else> goes with.  If you use C<unless> in place of C<if>,
the sense of the test is reversed.

The C<while> statement executes the block as long as the expression is
true (does not evaluate to the null string C<""> or C<0> or C<"0">).
The LABEL is optional, and if present, consists of an identifier followed
by a colon.  The LABEL identifies the loop for the loop control
statements C<next>, C<last>, and C<redo>.
If the LABEL is omitted, the loop control statement
refers to the innermost enclosing loop.  This may include dynamically
looking back your call-stack at run time to find the LABEL.  Such
desperate behavior triggers a warning if you use the C<use warnings>
pragma or the B<-w> flag.
Unlike a C<foreach> statement, a C<while> statement never implicitly
localises any variables.

If there is a C<continue> BLOCK, it is always executed just before the
conditional is about to be evaluated again, just like the third part of a
C<for> loop in C.  Thus it can be used to increment a loop variable, even
when the loop has been continued via the C<next> statement (which is
similar to the C C<continue> statement).

=head2 Loop Control

The C<next> command is like the C<continue> statement in C; it starts
the next iteration of the loop:

    LINE: while (<STDIN>) {
	next LINE if /^#/;	# discard comments
	...
    }

The C<last> command is like the C<break> statement in C (as used in
loops); it immediately exits the loop in question.  The
C<continue> block, if any, is not executed:

    LINE: while (<STDIN>) {
	last LINE if /^$/;	# exit when done with header
	...
    }

The C<redo> command restarts the loop block without evaluating the
conditional again.  The C<continue> block, if any, is I<not> executed.
This command is normally used by programs that want to lie to themselves
about what was just input.

For example, when processing a file like F</etc/termcap>.
If your input lines might end in backslashes to indicate continuation, you
want to skip ahead and get the next record.

    while (<>) {
	chomp;
	if (s/\\$//) {
	    $_ .= <>;
	    redo unless eof();
	}
	# now process $_
    }

which is Perl short-hand for the more explicitly written version:

    LINE: while (defined($line = <ARGV>)) {
	chomp($line);
	if ($line =~ s/\\$//) {
	    $line .= <ARGV>;
	    redo LINE unless eof(); # not eof(ARGV)!
	}
	# now process $line
    }

Note that if there were a C<continue> block on the above code, it would get
executed even on discarded lines.  This is often used to reset line counters 
or C<?pat?> one-time matches.

    # inspired by :1,$g/fred/s//WILMA/
    while (<>) {
	?(fred)?    && s//WILMA $1 WILMA/;
	?(barney)?  && s//BETTY $1 BETTY/;
	?(homer)?   && s//MARGE $1 MARGE/;
    } continue {
	print "$ARGV $.: $_";
	close ARGV  if eof();		# reset $.
	reset	    if eof();		# reset ?pat?
    }

If the word C<while> is replaced by the word C<until>, the sense of the
test is reversed, but the conditional is still tested before the first
iteration.

The loop control statements don't work in an C<if> or C<unless>, since
they aren't loops.  You can double the braces to make them such, though.

    if (/pattern/) {{
	next if /fred/;
	next if /barney/;
	# so something here
    }}

The form C<while/if BLOCK BLOCK>, available in Perl 4, is no longer
available.   Replace any occurrence of C<if BLOCK> by C<if (do BLOCK)>.

=head2 For Loops

Perl's C-style C<for> loop works like the corresponding C<while> loop;
that means that this:

    for ($i = 1; $i < 10; $i++) {
	...
    }

is the same as this:

    $i = 1;
    while ($i < 10) {
	...
    } continue {
	$i++;
    }

There is one minor difference: if variables are declared with C<my>
in the initialization section of the C<for>, the lexical scope of
those variables is exactly the C<for> loop (the body of the loop
and the control sections).

Besides the normal array index looping, C<for> can lend itself
to many other interesting applications.  Here's one that avoids the
problem you get into if you explicitly test for end-of-file on
an interactive file descriptor causing your program to appear to
hang.

    $on_a_tty = -t STDIN && -t STDOUT;
    sub prompt { print "yes? " if $on_a_tty }
    for ( prompt(); <STDIN>; prompt() ) {
	# do something
    }

=head2 Foreach Loops

The C<foreach> loop iterates over a normal list value and sets the
variable VAR to be each element of the list in turn.  If the variable
is preceded with the keyword C<my>, then it is lexically scoped, and
is therefore visible only within the loop.  Otherwise, the variable is
implicitly local to the loop and regains its former value upon exiting
the loop.  If the variable was previously declared with C<my>, it uses
that variable instead of the global one, but it's still localized to
the loop.  

The C<foreach> keyword is actually a synonym for the C<for> keyword, so
you can use C<foreach> for readability or C<for> for brevity.  (Or because
the Bourne shell is more familiar to you than I<csh>, so writing C<for>
comes more naturally.)  If VAR is omitted, C<$_> is set to each value.

If any element of LIST is an lvalue, you can modify it by modifying
VAR inside the loop.  Conversely, if any element of LIST is NOT an
lvalue, any attempt to modify that element will fail.  In other words,
the C<foreach> loop index variable is an implicit alias for each item
in the list that you're looping over.

If any part of LIST is an array, C<foreach> will get very confused if
you add or remove elements within the loop body, for example with
C<splice>.   So don't do that.

C<foreach> probably won't do what you expect if VAR is a tied or other
special variable.   Don't do that either.

Examples:

    for (@ary) { s/foo/bar/ }

    for my $elem (@elements) {
	$elem *= 2;
    }

    for $count (10,9,8,7,6,5,4,3,2,1,'BOOM') {
	print $count, "\n"; sleep(1);
    }

    for (1..15) { print "Merry Christmas\n"; }

    foreach $item (split(/:[\\\n:]*/, $ENV{TERMCAP})) {
	print "Item: $item\n";
    }

Here's how a C programmer might code up a particular algorithm in Perl:

    for (my $i = 0; $i < @ary1; $i++) {
	for (my $j = 0; $j < @ary2; $j++) {
	    if ($ary1[$i] > $ary2[$j]) {
		last; # can't go to outer :-(
	    }
	    $ary1[$i] += $ary2[$j];
	}
	# this is where that last takes me
    }

Whereas here's how a Perl programmer more comfortable with the idiom might
do it:

    OUTER: for my $wid (@ary1) {
    INNER:   for my $jet (@ary2) {
		next OUTER if $wid > $jet;
		$wid += $jet;
	     }
	  }

See how much easier this is?  It's cleaner, safer, and faster.  It's
cleaner because it's less noisy.  It's safer because if code gets added
between the inner and outer loops later on, the new code won't be
accidentally executed.  The C<next> explicitly iterates the other loop
rather than merely terminating the inner one.  And it's faster because
Perl executes a C<foreach> statement more rapidly than it would the
equivalent C<for> loop.

=head2 Basic BLOCKs and Switch Statements

A BLOCK by itself (labeled or not) is semantically equivalent to a
loop that executes once.  Thus you can use any of the loop control
statements in it to leave or restart the block.  (Note that this is
I<NOT> true in C<eval{}>, C<sub{}>, or contrary to popular belief
C<do{}> blocks, which do I<NOT> count as loops.)  The C<continue>
block is optional.

The BLOCK construct is particularly nice for doing case
structures.

    SWITCH: {
	if (/^abc/) { $abc = 1; last SWITCH; }
	if (/^def/) { $def = 1; last SWITCH; }
	if (/^xyz/) { $xyz = 1; last SWITCH; }
	$nothing = 1;
    }

There is no official C<switch> statement in Perl, because there are
already several ways to write the equivalent.

However, starting from Perl 5.8 to get switch and case one can use
the Switch extension and say:

	use Switch;

after which one has switch and case.  It is not as fast as it could be
because it's not really part of the language (it's done using source
filters) but it is available, and it's very flexible.

In addition to the above BLOCK construct, you could write

    SWITCH: {
	$abc = 1, last SWITCH  if /^abc/;
	$def = 1, last SWITCH  if /^def/;
	$xyz = 1, last SWITCH  if /^xyz/;
	$nothing = 1;
    }

(That's actually not as strange as it looks once you realize that you can
use loop control "operators" within an expression,  That's just the normal
C comma operator.)

or

    SWITCH: {
	/^abc/ && do { $abc = 1; last SWITCH; };
	/^def/ && do { $def = 1; last SWITCH; };
	/^xyz/ && do { $xyz = 1; last SWITCH; };
	$nothing = 1;
    }

or formatted so it stands out more as a "proper" C<switch> statement:

    SWITCH: {
	/^abc/ 	    && do {
			    $abc = 1;
			    last SWITCH;
		       };

	/^def/ 	    && do {
			    $def = 1;
			    last SWITCH;
		       };

	/^xyz/ 	    && do {
			    $xyz = 1;
			    last SWITCH;
		        };
	$nothing = 1;
    }

or

    SWITCH: {
	/^abc/ and $abc = 1, last SWITCH;
	/^def/ and $def = 1, last SWITCH;
	/^xyz/ and $xyz = 1, last SWITCH;
	$nothing = 1;
    }

or even, horrors,

    if (/^abc/)
	{ $abc = 1 }
    elsif (/^def/)
	{ $def = 1 }
    elsif (/^xyz/)
	{ $xyz = 1 }
    else
	{ $nothing = 1 }

A common idiom for a C<switch> statement is to use C<foreach>'s aliasing to make
a temporary assignment to C<$_> for convenient matching:

    SWITCH: for ($where) {
		/In Card Names/     && do { push @flags, '-e'; last; };
		/Anywhere/          && do { push @flags, '-h'; last; };
		/In Rulings/        && do {                    last; };
		die "unknown value for form variable where: `$where'";
	    }

Another interesting approach to a switch statement is arrange
for a C<do> block to return the proper value:

    $amode = do {
	if     ($flag & O_RDONLY) { "r" }	# XXX: isn't this 0?
	elsif  ($flag & O_WRONLY) { ($flag & O_APPEND) ? "a" : "w" }
	elsif  ($flag & O_RDWR)   {
	    if ($flag & O_CREAT)  { "w+" }
	    else                  { ($flag & O_APPEND) ? "a+" : "r+" }
	}
    };

Or 

        print do {
            ($flags & O_WRONLY) ? "write-only"          :
            ($flags & O_RDWR)   ? "read-write"          :
                                  "read-only";
        };

Or if you are certainly that all the C<&&> clauses are true, you can use
something like this, which "switches" on the value of the
C<HTTP_USER_AGENT> environment variable.

    #!/usr/bin/perl 
    # pick out jargon file page based on browser
    $dir = 'http://www.wins.uva.nl/~mes/jargon';
    for ($ENV{HTTP_USER_AGENT}) { 
	$page  =    /Mac/            && 'm/Macintrash.html'
		 || /Win(dows )?NT/  && 'e/evilandrude.html'
		 || /Win|MSIE|WebTV/ && 'm/MicroslothWindows.html'
		 || /Linux/          && 'l/Linux.html'
		 || /HP-UX/          && 'h/HP-SUX.html'
		 || /SunOS/          && 's/ScumOS.html'
		 ||                     'a/AppendixB.html';
    }
    print "Location: $dir/$page\015\012\015\012";

That kind of switch statement only works when you know the C<&&> clauses
will be true.  If you don't, the previous C<?:> example should be used.

You might also consider writing a hash of subroutine references
instead of synthesizing a C<switch> statement.

=head2 Goto

Although not for the faint of heart, Perl does support a C<goto>
statement.  There are three forms: C<goto>-LABEL, C<goto>-EXPR, and
C<goto>-&NAME.  A loop's LABEL is not actually a valid target for
a C<goto>; it's just the name of the loop.

The C<goto>-LABEL form finds the statement labeled with LABEL and resumes
execution there.  It may not be used to go into any construct that
requires initialization, such as a subroutine or a C<foreach> loop.  It
also can't be used to go into a construct that is optimized away.  It
can be used to go almost anywhere else within the dynamic scope,
including out of subroutines, but it's usually better to use some other
construct such as C<last> or C<die>.  The author of Perl has never felt the
need to use this form of C<goto> (in Perl, that is--C is another matter).

The C<goto>-EXPR form expects a label name, whose scope will be resolved
dynamically.  This allows for computed C<goto>s per FORTRAN, but isn't
necessarily recommended if you're optimizing for maintainability:

    goto(("FOO", "BAR", "GLARCH")[$i]);

The C<goto>-&NAME form is highly magical, and substitutes a call to the
named subroutine for the currently running subroutine.  This is used by
C<AUTOLOAD()> subroutines that wish to load another subroutine and then
pretend that the other subroutine had been called in the first place
(except that any modifications to C<@_> in the current subroutine are
propagated to the other subroutine.)  After the C<goto>, not even C<caller()>
will be able to tell that this routine was called first.

In almost all cases like this, it's usually a far, far better idea to use the
structured control flow mechanisms of C<next>, C<last>, or C<redo> instead of
resorting to a C<goto>.  For certain applications, the catch and throw pair of
C<eval{}> and die() for exception processing can also be a prudent approach.

=head2 PODs: Embedded Documentation

Perl has a mechanism for intermixing documentation with source code.
While it's expecting the beginning of a new statement, if the compiler
encounters a line that begins with an equal sign and a word, like this

    =head1 Here There Be Pods!

Then that text and all remaining text up through and including a line
beginning with C<=cut> will be ignored.  The format of the intervening
text is described in L<perlpod>.

This allows you to intermix your source code
and your documentation text freely, as in

    =item snazzle($)

    The snazzle() function will behave in the most spectacular
    form that you can possibly imagine, not even excepting
    cybernetic pyrotechnics.

    =cut back to the compiler, nuff of this pod stuff!

    sub snazzle($) {
	my $thingie = shift;
	.........
    }

Note that pod translators should look at only paragraphs beginning
with a pod directive (it makes parsing easier), whereas the compiler
actually knows to look for pod escapes even in the middle of a
paragraph.  This means that the following secret stuff will be
ignored by both the compiler and the translators.

    $a=3;
    =secret stuff
     warn "Neither POD nor CODE!?"
    =cut back
    print "got $a\n";

You probably shouldn't rely upon the C<warn()> being podded out forever.
Not all pod translators are well-behaved in this regard, and perhaps
the compiler will become pickier.

One may also use pod directives to quickly comment out a section
of code.

=head2 Plain Old Comments (Not!)

Much like the C preprocessor, Perl can process line directives.  Using
this, one can control Perl's idea of filenames and line numbers in
error or warning messages (especially for strings that are processed
with C<eval()>).  The syntax for this mechanism is the same as for most
C preprocessors: it matches the regular expression
C</^#\s*line\s+(\d+)\s*(?:\s"([^"]+)")?\s*$/> with C<$1> being the line
number for the next line, and C<$2> being the optional filename
(specified within quotes).

There is a fairly obvious gotcha included with the line directive:
Debuggers and profilers will only show the last source line to appear
at a particular line number in a given file.  Care should be taken not
to cause line number collisions in code you'd like to debug later.

Here are some examples that you should be able to type into your command
shell:

    % perl
    # line 200 "bzzzt"
    # the `#' on the previous line must be the first char on line
    die 'foo';
    __END__
    foo at bzzzt line 201.

    % perl
    # line 200 "bzzzt"
    eval qq[\n#line 2001 ""\ndie 'foo']; print $@;
    __END__
    foo at - line 2001.

    % perl
    eval qq[\n#line 200 "foo bar"\ndie 'foo']; print $@;
    __END__
    foo at foo bar line 200.

    % perl
    # line 345 "goop"
    eval "\n#line " . __LINE__ . ' "' . __FILE__ ."\"\ndie 'foo'";
    print $@;
    __END__
    foo at goop line 345.

=cut