in reply to Regex with multiple pattern omissions

sub extract_terms(){
my $input = shift;
chomp $input;

[download]

Your prototype says "accept NO arguments" for this subroutine.    Your next statement says that this subroutine accepts ONE argument.    Do not use prototypes unless you are attempting to imitate one of Perl's built-in functions.

Far More than Everything You've Ever Wanted to Know about Prototypes in Perl -- by Tom Christiansen

Your use of chomp here implies that this subroutine only deals with lines input from files?    Where is the rest of the file line handling code?

Replies are listed 'Best First'.
Re^2: Regex with multiple pattern omissions
by jhoop (Acolyte) on Jan 09, 2011 at 02:06 UTC
    I think I just copied the starting lines of this subroutine in from one of the other subroutines, chomp doesn't need to be there. I'm pretty new to this, and so may be using shift incorrectly/unnecessarily, but this has worked so far. The input for this subroutine is a block of text consisting of a (long) list of \n-separated search-strings. For this routine, I don't need them split, as I'm extracting the pertinent terms from ALL searches and compiling an alphabetized list of non-dupes.
[reply]
      I think you have mis-understood the comment about prototypes. I suspect that you probably didn't even know that you were declaring a prototype.

      The simple explanation is: when you define a sub X, do not put parens, () after the name.
      That's it.
      sub X(){} means something very different than just sub X{}.
      I would go as far as to say that you never have to, and normally should not put any (....stuff...) after the sub's name.

      -What you have done with shift is 100% correct.
      -Maybe chomp() is not necessary, but it doesn't "hurt".
      -A more important point for me is to indent the lines within the subroutine by either 3 or 4 spaces.

      "Prototype failure" example: 

      #!/usr/bin/perl -w
use strict;

# This sequence works, although with a warning...
# because Perl hasn't yet seen subroutine X.

X("xyz");

sub X()  # this means that subroutine X cannot 
         # be called with any arugment at all.
         # sub X();      #is ok, 
         # sub X("abc"); #is not ok.
{
   my $input = shift;
   print "$input\n";
}

#this would fail to produce a result - program fails to compile
# X("abc");  
# because now that subroutine X() has been seen, it is understood
# that no arguments can be passed to it.

__END__
prints:
main::X() called too early to check prototype at C:\TEMP\prototypes.pl
+ line 4.
xyz

      [download]
[reply]
[d/l]
        You're right, I didn't realize what the () were for.. I thought they were necessary anytime arguments are passed in. Looking back, I'll bet this has been the unknown source of some of my debugging frustration in the past.. Thanks for the helpful pointers! I usually have a healthy OCD for indenting, when I pasted the code it looked like the formatting got weird in the entry form, so i deleted the tabs..
[reply]

In Section Seekers of Perl Wisdom