Nevertheless I'm still interested why now the use of the variable $prefixSnmpWalk works.

In the code you showed it always worked, your problem was always the input 

# some declarations in the beginnings
  my $TAB                 =   "\t";
  my $SPACE               =   " ";
  my $oidNbrSysDescr      =   ".1.3.6.1.2.1.1.1";
  my $prefixSysDescr      =   quotemeta 'system.sysDescr.0 : DISPLAY S
+TRING- (ascii):  ';
  my $prefixSnmpWalk      =   'snmpwalk:\s*'; # no use ??



my $sysDescr  = q~
snmpwalk:        yeah
~;
      for ( $sysDescr ) {

         /$prefixSysDescr/ && do {
            s/$prefixSysDescr/$hostName$TAB/;
            $OutputLine = $_;
            last;
         }; # substitute some prefixes (this one works)

#         /snmpwalk:\s*/
        /$prefixSnmpWalk/
         && do {
            s/snmpwalk:\s*/$hostName$TAB/;
            $OutputLine = $_;
            last;
         }; # error messages starting with "snmpwalk:  "
            # here is the problem. All of a sudden I coudln't
            # use $prefixSnmpWalk anymore. Even quotemeta
            # failed

         $OutputLine = $OutputLine . $SPACE . $_;

      } # process output

die "$OutputLine ";
__END__

        yeah
  at - line 36.

[download]

In reply to Re^3: His strangeness regex by Anonymous Monk
in thread His strangeness regex by o_chfa

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.