warn
warn
warn LIST
Prints the value of LIST to STDERR. If the last element of LIST does not end in a newline, it appends the same file/line number text as die
does-
If the output is empty and $@
already contains a value (typically from a previous eval) that value is used after appending "\t...caught"
to $@
. This is useful for staying almost, but not entirely similar to die
-
If $@
is empty then the string "Warning: Something's wrong"
is used.
No message is printed if there is a $SIG{__WARN__}
handler installed. It is the handler's responsibility to deal with the message as it sees fit (like, for instance, converting it into a die
)- Most handlers must therefore arrange to actually display the warnings that they are not prepared to deal with, by calling warn
again in the handler- Note that this is quite safe and will not produce an endless loop, since __WARN__
hooks are not called from inside one.
You will find this behavior is slightly different from that of $SIG{__DIE__}
handlers (which don't suppress the error text, but can instead call die
again to change it)-
Using a __WARN__
handler provides a powerful way to silence all warnings (even the so-called mandatory ones). An example:
# wipe out *all* compile-time warnings BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } } my $foo = 10; my $foo = 20; # no warning about duplicate my $foo, # but hey, you asked for it! # no compile-time or run-time warnings before here $DOWARN = 1; # run-time warnings enabled after here warn "\$foo is alive and $foo!"; # does show up
See perlvar for details on setting %SIG
entries and for more examples. See the Carp module for other kinds of warnings using its carp() and cluck() functions.
© 1993–2016 Larry Wall and others
Licensed under the GNU General Public License version 1 or later, or the Artistic License.
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http://perldoc.perl.org/5.20.2/functions/warn.html