Meaning of $SIG{...} = 'DEFAULT';

[repellent]

In perlipc:

You may also choose to assign the strings 'IGNORE' or 'DEFAULT' as the handler, in which case Perl will try to discard the signal or do the default thing.

What does it mean by "do the default thing"? Where can I get documentation on 'DEFAULT' behaviors for different signals, if any?

[JadeNB]

perlipc says that Perl's handling of signals is based on the signal(3) function from the C library, so I imagine that man 3 signal—in particular, the 'default action' column—will give the information you want.

[repellent]

Thanks! A quick search yields: signal(3)

[repellent]

FYI: I have compiled a list of signals and their numbers, with brief descriptions. There may be differences in signal numbers depending on the platform. If there is only one signal number stated, then it is the same for all the platforms. The alphabetic [A-F] legends are at the bottom.


          alpha/sparc,
           i386/ppc,
             mips

SIGHUP         1       A  Hangup detected on controlling terminal
                            or death of controlling process
SIGINT         2       A  Interrupt from keyboard (Ctrl-C)
SIGQUIT        3       C  Quit from keyboard
SIGILL         4       C  Illegal Instruction
SIGTRAP        5       C  Trace/breakpoint trap
SIGABRT        6       C  Abort signal from abort
SIGBUS     10, 7,10    C  Bus error (bad memory access)
SIGFPE         8       C  Floating point exception
SIGKILL        9     AEF  Kill (cannot be caught or ignored)
SIGUSR1    30,10,16    A  User-defined signal 1
SIGSEGV       11       C  Invalid memory reference
SIGUSR2    31,12,17    A  User-defined signal 2
SIGPIPE       13       A  Broken pipe: write to pipe with no readers
SIGALRM       14       A  Timer signal from alarm
SIGTERM       15       A  Termination (termination signal from SIGKILL
+)
SIGSTKFLT   -,16, -    A  Stack fault on coprocessor
SIGCHLD    20,17,18    B  Child stopped or terminated
SIGCONT    19,18,25       Continue if stopped
SIGSTOP    17,19,23  DEF  Stop process
SIGTSTP    18,20,24    D  Stop typed at tty
SIGTTIN    21,21,26    D  tty input for background process
SIGTTOU    22,22,27    D  tty output for background process
SIGURG     16,23,21    B  Urgent condition on socket (4.2 BSD)
SIGXCPU    24,24,30    C  CPU time limit exceeded (4.2 BSD)
SIGXFSZ    25,25,31    C  File size limit exceeded (4.2 BSD)
SIGVTALRM  26,26,28    A  Virtual alarm clock (4.2 BSD)
SIGPROF    27,27,29    A  Profiling timer expired
SIGIO      23,29,22    A  I/O now possible (4.2 BSD)
SIGWINCH   28,28,20    B  Window resize signal (4.3 BSD, Sun)
SIGPWR     29,30,19    A  Power failure (System V)
SIGUNUSED   -,31, -    A  Unused signal (will be SIGSYS)

SIGCLD     -,  -,18    A  [synonym for SIGCHLD]
SIGIOT         6       C  IOT trap [synonym for SIGABRT]
SIGINFO    29, -, -    A  [synonym for SIGPWR]
SIGPOLL    23,29,22    A  Pollable event (Sys V) [synonym for SIGIO]
SIGEMT      7, -, 7    A
SIGLOST     -, -, -    A  File lock lost
SIGSYS     12, -,12    C  Bad argument to routine (SVID)

A = default action terminate process
B = default action ignore signal
C = default action terminate process and dump core
D = default action stop process
E = signal cannot be caught
F = signal cannot be ignored

[oko1]

You forgot the most important ones.

Unix Error Messages

At the USENIX Association conference in Atlanta recently (Ed: 1985/198
+6) 
a contest was held to invent the most humorous/bizarre/etc. UN*X error
+ 
message of the errno(2) 'EERROR' type. This contest had been tried at 
+an 
earlier European Users Group meeting, where the winning entry was

ENOTOBACCO - Read on an empty pipe

You get the idea. A partial (alphabetized) list of 'top(?)' entries fr
+om 
Atlanta (and from several readers of hp.unix) follows; if your pun/wei
+rdness 
tolerance is low, you may want to abandon ship:

EBEFOREI - Invalid syntax
ECHERNOBYL - Core dumped
ECRAY - Program exited before being run
EDINGDONG - The daemon is dead
EFLAT - System needs tuning
EGEEK - Program written by inept Frat member
EIEIO - Here-a-bug, there-a-bug, ....
EIUD - Missing period
ELECTROLUX - Your code could stand to be cleaned up
EMILYPOST - Wrong fork
END.ARMS.CONTROL - Silo overflow
ENOHORSE - Mount failed
ENONSEQUITUR - C program not derived from main(){printf("Hello, world"
+);}
EWATERGATE - Extended tape gap
EWOK - Aliens sighted
EWOK - Your code appears to have been stir-fried
EWOULDBNICE - The feature you want has not been implemented yet

And finally, a sort-of 'period piece':

EMR.ED -

    A host is a host,
    From coast to coast
    And nobody talks to a host that's close,
    Unless the host that isn't close
    Is busy, hung, or dead.

I would also like this new signal to be supported:

SIGNUKE - Nuclear event occurred (cannot be caught or ignored :-)

:) :) :)

[Anonymous Monk]

What does it mean by "do the default thing"?

Test it :D

# $SIG{...} = sub {warn "NOT DEFAULT " ...};  # commented out to see d
+efault