#!/usr/bin/perl

print "my pid = $$\n";

get_lock();
   print "enter return again:";
   my $x = <STDIN>;

sub get_lock {
   local($0) = "(acquiring lock)";
   print "enter return:";
   my $x = <STDIN>;
}

##</code><code>##

$ /bin/ps 27940
  PID TTY      STAT   TIME COMMAND
27940 pts/0    S+     0:00 (acquiring lock)
$ /bin/ps 27940
  PID TTY      STAT   TIME COMMAND
27940 pts/0    S+     0:00 ./d0