Produces a message on STDERR just likedie, but doesn't exit or throw an exception.
If LIST 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 todie.
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 adie). Most handlers must therefore make arrangements to actually display the warnings that they are not prepared to deal with, by callingwarn 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 calldie 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 warningsBEGIN { $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 herewarn "\$foo is alive and $foo!"; # does show upSeeperlvar 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.
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