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Re: $! or &Errno or $!{}

by jlawrenc (Scribe)
on Mar 21, 2001 at 01:49 UTC ( #65834=note: print w/replies, xml ) Need Help??

in reply to $! or &Errno or $!{}

I was confused by this as well. My cause to delve into IO::Socket was a breakdown of my LWP modules.

Go to your Perl source can check out:

the directory ext/Errno

This is where these strings are actually obtained and made into the module which in turn gives rise to %!.

What is going on here is that at make time Errno_pm.PL actually checks the cpp output to get a list of headers to scan. This output comes from something along the lines of "cpp your cpp flags errno.c". "errno.c" has a single line "#include <errno.h> Then it will scan all of these header files for #defines. (check out /usr/lib/errno.h or /usr/lib/asm/errno.h if you have it). Taking these defines, it will write the code for "" which ultimately lives in "lib/perl5/5.6.0/<arch>/

The values for %! are supplied via a tied hash from

Why do I know this? Well because shipped with RedHat did not correctly report all of the headers to scan. When the IO::Socket went to test against $!{EINPROGRESS} it did not match. It was always giving me "Timeout" messages. :( After tracing this through I found the defective output from cpp and the rest is history.

You need the updated cpp that RedHat supplies. This version (dated Dec 18, 2000) works correctly.