I ran podchecker on your program and received these messages: 

$ podchecker 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 34 in file 747546.pl
*** ERROR: =item without previous =over at line 130 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 141 in file 747546.pl
*** ERROR: Spurious text after =cut at line 135 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 158 in file 747546.pl
*** ERROR: Spurious text after =cut at line 156 in file 747546.pl
*** ERROR: =item without previous =over at line 360 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 378 in file 747546.pl
*** ERROR: Spurious text after =cut at line 372 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 485 in file 747546.pl
*** ERROR: Spurious text after =cut at line 480 in file 747546.pl
*** ERROR: =item without previous =over at line 527 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 533 in file 747546.pl
*** ERROR: =item without previous =over at line 716 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 719 in file 747546.pl
*** WARNING: line containing nothing but whitespace in paragraph at li
+ne 721 in file 747546.pl
*** ERROR: Spurious text after =cut at line 787 in file 747546.pl
747546.pl has 9 pod syntax errors.

[download]

Then I ran the compiler on it and got a syntax error: 

$ perl -c 747546.pl
syntax error at 747546.pl line 681, near "next "

[download]

Because you are missing a semicolon on the previous line. 

191:                    open(CACHE_FH," < $cache");
212:            open(F,">$cache");
425:                    open(FILE, ">$cache");
677:                    open(CACHE_FH, "< $cache");
700:            open(F,">$cache");

[download]

Also, you should verify that open succeeded before you try to use a possibly invalid filehandle.

Update 

411:                    stdout::debug("BroadcastPing: Read $#lines lin
+es from $cache\n");
421:                    stdout::debug("BroadcastPing: Writing $#keys l
+ines to $cache\n");
926:                    stdout::debug("read_arptable(): ARP Read: Read
+ $#lines lines from $arp_cachefile\n");

[download]

The variables $#lines and $#keys do not contain the number of lines, they contain the last index of the arrays @lines and @keys.   You need to use the array in scalar context to get the correct number: 

                        stdout::debug("BroadcastPing: Read " . @lines 
+. " lines from $cache\n");
                        stdout::debug("BroadcastPing: Writing " . @key
+s . " lines to $cache\n");
                        stdout::debug("read_arptable(): ARP Read: Read
+ " . @lines . " lines from $arp_cachefile\n");

[download]

In reply to Re: Class-C subnet discovery/scanner by jwkrahn
in thread Class-C subnet discovery/scanner by jbryan

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