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

In reply to Re: perl SIGnal process by kcott
in thread perl SIGnal process by chinaxing

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.