5 carp - warn of errors (from perspective of caller)
7 cluck - warn of errors with stack backtrace
8 (not exported by default)
10 croak - die of errors (from perspective of caller)
12 confess - die of errors with stack backtrace
17 croak "We're outta here!";
20 cluck "This is how we got here!";
24 The Carp routines are useful in your own modules because
25 they act like die() or warn(), but report where the error
26 was in the code they were called from. Thus if you have a
27 routine Foo() that has a carp() in it, then the carp()
28 will report the error as occurring where Foo() was called,
29 not where carp() was called.
31 =head2 Forcing a Stack Trace
33 As a debugging aid, you can force Carp to treat a croak as a confess
34 and a carp as a cluck across I<all> modules. In other words, force a
35 detailed stack trace to be given. This can be very helpful when trying
36 to understand why, or from where, a warning or error is being generated.
38 This feature is enabled by 'importing' the non-existant symbol
39 'verbose'. You would typically enable it by saying
41 perl -MCarp=verbose script.pl
43 or by including the string C<MCarp=verbose> in the L<PERL5OPT>
48 # This package is heavily used. Be small. Be fast. Be good.
50 # Comments added by Andy Wardley <abw@kfs.org> 09-Apr-98, based on an
51 # _almost_ complete understanding of the package. Corrections and
52 # comments are welcome.
54 # The $CarpLevel variable can be set to "strip off" extra caller levels for
55 # those times when Carp calls are buried inside other functions. The
56 # $Max(EvalLen|(Arg(Len|Nums)) variables are used to specify how the eval
57 # text and function arguments should be formatted when printed.
59 $CarpLevel = 0; # How many extra package levels to skip on carp.
60 $MaxEvalLen = 0; # How much eval '...text...' to show. 0 = all.
61 $MaxArgLen = 64; # How much of each argument to print. 0 = all.
62 $MaxArgNums = 8; # How many arguments to print. 0 = all.
66 @EXPORT = qw(confess croak carp);
67 @EXPORT_OK = qw(cluck verbose);
68 @EXPORT_FAIL = qw(verbose); # hook to enable verbose mode
71 # if the caller specifies verbose usage ("perl -MCarp=verbose script.pl")
72 # then the following method will be called by the Exporter which knows
73 # to do this thanks to @EXPORT_FAIL, above. $_[1] will contain the word
78 if ($_[0] eq 'verbose') {
79 local $^W = 0; # avoid "sub-routine redefined..." warning
80 *shortmess = \&longmess; # set shortmess() as an alias to longmess()
81 shift; # remove 'verbose' from the args to keep Exporter happy
87 # longmess() crawls all the way up the stack reporting on all the function
88 # calls made. The error string, $error, is originally constructed from the
89 # arguments passed into longmess() via confess(), cluck() or shortmess().
90 # This gets appended with the stack trace messages which are generated for
91 # each function call on the stack.
94 my $error = join '', @_;
96 my $i = 1 + $CarpLevel;
97 my ($pack,$file,$line,$sub,$hargs,$eval,$require);
100 # crawl up the stack....
102 while (do { { package DB; @a = caller($i++) } } ) {
103 # get copies of the variables returned from caller()
104 ($pack,$file,$line,$sub,$hargs,undef,$eval,$require) = @a;
106 # if the $error error string is newline terminated then it
107 # is copied into $mess. Otherwise, $mess gets set (at the end of
108 # the 'else {' section below) to one of two things. The first time
109 # through, it is set to the "$error at $file line $line" message.
110 # $error is then set to 'called' which triggers subsequent loop
111 # iterations to append $sub to $mess before appending the "$error
112 # at $file line $line" which now actually reads "called at $file line
113 # $line". Thus, the stack trace message is constructed:
115 # first time: $mess = $error at $file line $line
116 # subsequent times: $mess .= $sub $error at $file line $line
119 if ($error =~ m/\n$/) {
122 # Build a string, $sub, which names the sub-routine called.
123 # This may also be "require ...", "eval '...' or "eval {...}"
126 $sub = "require $eval";
128 $eval =~ s/([\\\'])/\\$1/g;
129 if ($MaxEvalLen && length($eval) > $MaxEvalLen) {
130 substr($eval,$MaxEvalLen) = '...';
132 $sub = "eval '$eval'";
134 } elsif ($sub eq '(eval)') {
137 # if there are any arguments in the sub-routine call, format
138 # them according to the format variables defined earlier in
139 # this file and join them onto the $sub sub-routine string
141 # we may trash some of the args so we take a copy
142 @a = @DB::args; # must get local copy of args
143 # don't print any more than $MaxArgNums
144 if ($MaxArgNums and @a > $MaxArgNums) {
145 # cap the length of $#a and set the last element to '...'
150 # set args to the string "undef" if undefined
151 $_ = "undef", next unless defined $_;
153 # dunno what this is for...
159 # terminate the string early with '...' if too long
160 substr($_,$MaxArgLen) = '...'
161 if $MaxArgLen and $MaxArgLen < length;
163 # 'quote' arg unless it looks like a number
164 $_ = "'$_'" unless /^-?[\d.]+$/;
165 # print high-end chars as 'M-<char>' or '^<char>'
166 s/([\200-\377])/sprintf("M-%c",ord($1)&0177)/eg;
167 s/([\0-\37\177])/sprintf("^%c",ord($1)^64)/eg;
169 # append ('all', 'the', 'arguments') to the $sub string
170 $sub .= '(' . join(', ', @a) . ')';
172 # here's where the error message, $mess, gets constructed
173 $mess .= "\t$sub " if $error eq "called";
174 $mess .= "$error at $file line $line\n";
176 # we don't need to print the actual error message again so we can
177 # change this to "called" so that the string "$error at $file line
178 # $line" makes sense as "called at $file line $line".
181 # this kludge circumvents die's incorrect handling of NUL
182 my $msg = \($mess || $error);
188 # shortmess() is called by carp() and croak() to skip all the way up to
189 # the top-level caller's package and report the error from there. confess()
190 # and cluck() generate a full stack trace so they call longmess() to
191 # generate that. In verbose mode shortmess() is aliased to longmess() so
192 # you always get a stack trace
194 sub shortmess { # Short-circuit &longmess if called via multiple packages
195 my $error = join '', @_;
196 my ($prevpack) = caller(1);
197 my $extra = $CarpLevel;
199 my ($pack,$file,$line);
200 # when reporting an error, we want to report it from the context of the
201 # calling package. So what is the calling package? Within a module,
202 # there may be many calls between methods and perhaps between sub-classes
203 # and super-classes, but the user isn't interested in what happens
204 # inside the package. We start by building a hash array which keeps
205 # track of all the packages to which the calling package belongs. We
206 # do this by examining its @ISA variable. Any call from a base class
207 # method (one of our caller's @ISA packages) can be ignored
208 my %isa = ($prevpack,1);
210 # merge all the caller's @ISA packages into %isa.
211 @isa{@{"${prevpack}::ISA"}} = ()
212 if(defined @{"${prevpack}::ISA"});
214 # now we crawl up the calling stack and look at all the packages in
215 # there. For each package, we look to see if it has an @ISA and then
216 # we see if our caller features in that list. That would imply that
217 # our caller is a derived class of that package and its calls can also
219 while (($pack,$file,$line) = caller($i++)) {
220 if(defined @{$pack . "::ISA"}) {
221 my @i = @{$pack . "::ISA"};
224 # merge any relevant packages into %isa
226 if(exists $i{$prevpack} || exists $isa{$pack});
229 # and here's where we do the ignoring... if the package in
230 # question is one of our caller's base or derived packages then
231 # we can ignore it (skip it) and go onto the next (but note that
232 # the continue { } block below gets called every time)
234 if(exists $isa{$pack});
236 # Hey! We've found a package that isn't one of our caller's
237 # clan....but wait, $extra refers to the number of 'extra' levels
238 # we should skip up. If $extra > 0 then this is a false alarm.
239 # We must merge the package into the %isa hash (so we can ignore it
240 # if it pops up again), decrement $extra, and continue.
243 @isa{@{$pack . "::ISA"}} = ()
244 if(defined @{$pack . "::ISA"});
247 # OK! We've got a candidate package. Time to construct the
248 # relevant error message and return it. die() doesn't like
249 # to be given NUL characters (which $msg may contain) so we
251 (my $msg = "$error at $file line $line\n") =~ tr/\0//d;
259 # uh-oh! It looks like we crawled all the way up the stack and
260 # never found a candidate package. Oh well, let's call longmess
261 # to generate a full stack trace. We use the magical form of 'goto'
262 # so that this shortmess() function doesn't appear on the stack
263 # to further confuse longmess() about it's calling package.
268 # the following four functions call longmess() or shortmess() depending on
269 # whether they should generate a full stack trace (confess() and cluck())
270 # or simply report the caller's package (croak() and carp()), respectively.
271 # confess() and croak() die, carp() and cluck() warn.
273 sub croak { die shortmess @_ }
274 sub confess { die longmess @_ }
275 sub carp { warn shortmess @_ }
276 sub cluck { warn longmess @_ }