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Tip of the Day
Language: Perl
Expertise: Beginner
Sep 11, 2003

A Quick-and-dirty Script for "Direct Mode" in Perl

Ever get annoyed that there's no "direct mode" environment in Perl? Instead, you have to save your code to a file and then execute it everytime. To offset this, I wrote this small program allows me to type and execute Perl code, complete statement by statement.

Here's how to use it. Save the code to a file named 'direct.pl', and start it. When the ">" prompt shows, type (or copy & paste from notepad) your code. When you press enter, it will execute it, show the result, and wait for next line. This script is quick-and-dirty—meaning it's not perfect and may not work every time but hey, that's not the point. It will try to count and show the number of open brackets/braces/parenthesis for you, and will execute the statement only when you close them.


my $count = 0;
my $statement = "";
print "\n> ";
while (<>) {
  chomp;
  s/([^\$\\])\#.*$/$1/;
  while (/{|\(|\[/g) {$count++};
  while (/}|\)|\]/g) {$count--};
  $statement .= $_;
  if (!$count) {
    $_ = eval $statement;
    print "\n[$_]\n";
    if ($@) {print "Error: $@\n"};
    $statement = " ";
    print "> ";
  }
  else {
    print "$count> ";
  }
}
Atanas Banov
 
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