fix getopt.awk first long option parsing

[Przemek Kitszel]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -DNDEBUG
uname output: Linux pkitszel-desk 6.0.9-100.fc35.x86_64 #1 SMP PREEMPT_DYNAMIC 
Wed Nov 16 17:25:52 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Gawk Version: 5.2.1

Attestation 1:
        I have read 
https://www.gnu.org/software/gawk/manual/html_node/Bugs.html.
        Yes

Attestation 2:
        I have not modified the sources before building gawk.
        True

Description:
        First long option of getopt() distributed with gawk fails to accept 
value.

Repeat-By:
        Following program demonstrates the problem:
                #!/usr/bin/gawk -f
                @include "getopt"
                BEGIN {
                        while ((opt = getopt(ARGC, ARGV, "", "iface:")) != -1) {
                                print opt, Optarg
                        }
                }
        Executed like: prog.awk -- --iface=eth0
        Should print "iface eth0", but prints only "iface ".

Fix:
        Apply my patch, either from Github Gist:
        https://gist.github.com/pkitszel/4027229617708b0a06ae8a6137a015a5
        or attached at the end below.
Thanks,
Przemek

First longopt option should have params properly assigned by now.
The bug was that old code assumed index offset of 1 for ",", which
is not necessairly at the very begining.
---
 getopt.awk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/getopt.awk b/getopt.awk
index 69944f3fe724..1cf205bae863 100644
--- a/getopt.awk
+++ b/getopt.awk
@@ -78,7 +78,7 @@ function getopt(argc, argv, options, longopts,    thisopt, i, 
j)
             Optind++
             return "?"
         }
-        if (substr(longopts, i+1+length(thisopt), 1) == ":") {
+        if (substr(longopts, i-1+RLENGTH, 1) == ":") {
             if (j > 0)
                 Optarg = substr(argv[Optind], j + 1)
             else
-- 
2.38.1