perl SIGnal process

chinaxing has asked for the wisdom of the Perl Monks concerning the following question:

I exploit the %SIG hash, found most of values are "undef", some of are "IGNORE";

perl -MData::Dumper -E ' print Dumper \%SIG '
[download]

What confuse me is that, if SIGnal's process was set to undef,

how the signal will be processed when it come up ? ( ignore ? call the default action defined by OS ?)

BTW, if I want to set SIGPIPE 's handle to default; how can i to get it ?

$SIG{PIPE} = undef 

or 

$SIG{PIPE} = ""

or 

#some thing else;
[download]

very thanks your patient to answer this :)

Comment on perl SIGnal process Select or Download Code

Replies are listed 'Best First'.
Re: perl SIGnal process by betterworld (Curate) on Aug 08, 2013 at 12:00 UTC
The operating system has its default ways to treat signals. Special application code is executed only if a signal handler is explicitly installed. If there is no handler, some default action will be taken, which should be documented. My system has informative man pages for "signal" in sections 7 and 2. Setting a signal to its default behavior is documented in perlvar: `$SIG{'INT'} = 'DEFAULT'; # restore default action $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT` [download]	[reply] [d/l]
Re^2: perl SIGnal process by chinaxing (Acolyte) on Aug 19, 2013 at 07:56 UTC
thank you ! but what's mean of undef , equals to 'DEFAULT' ? ; so does : `$SIG{'INT'} = 'DEFAULT'` [download] equals to `$SIG{'INT'} = undef` [download] ? very thanks your explaination :)	[reply] [d/l] [select]
Re: perl SIGnal process by kcott (Archbishop) on Aug 09, 2013 at 05:12 UTC
G'day chinaxing, For further documentation, take a look at perlipc - Signals. For setting defaults, why not capture the starting values and then reapply the defaults if you need to: $ perl -Mstrict -Mwarnings -E ' my %default_signal_for = %SIG; say "* Starting values "; say "SIG{USR1}: ", $SIG{USR1} // "<undef>"; say "DEF{USR1}: ", $default_signal_for{USR1} // "<undef>"; $SIG{USR1} = sub { 1 }; say " After setting USR1 "; say "SIG{USR1}: ", $SIG{USR1} // "<undef>"; say "DEF{USR1}: ", $default_signal_for{USR1} // "<undef>"; $SIG{USR1} = $default_signal_for{USR1}; say " Back to default values "; say "SIG{USR1}: ", $SIG{USR1} // "<undef>"; say "DEF{USR1}: ", $default_signal_for{USR1} // "<undef>"; ' Starting values * SIG{USR1}: <undef> DEF{USR1}: <undef> * After setting USR1 * SIG{USR1}: CODE(0x7fa4008401b0) DEF{USR1}: <undef> * Back to default values * SIG{USR1}: <undef> DEF{USR1}: <undef> [download] -- Ken	[reply] [d/l]
Re^2: perl SIGnal process by chinaxing (Acolyte) on Aug 19, 2013 at 07:57 UTC
yes! but i want to known difference between set to `'undef', "" and 'DEFAULT';`	[reply] [d/l]