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Why is my result empty?

by Anonymous Monk
on Mar 20, 2014 at 00:04 UTC ( #1079022=perlquestion: print w/ replies, xml ) Need Help??
Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I am trying to use strict perl coding for this simple task, but my variable returns empty. Why?
use strict; my $final_res=''; open FILE, $infile; while(my $final_line=<FILE>) { if($final_line=~/^SeqID/) { my $final_line=<FILE>; chomp $final_line; my @split_final=split(/\t/, $final_line); my $final_res = $split_final[7]; $final_res=~s/D/M/g; $final_res=~s/U/M/g; #print $final_res."\n"; } } close FILE; print $final_res."\n";

If I print inside the loop, in the comment, it prints fine. what am I missing?

Comment on Why is my result empty?
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Re: Why is my result empty?
by toolic (Chancellor) on Mar 20, 2014 at 00:14 UTC
      Damn! Silly mistake :)
      Thank you!
Re: Why is my result empty?
by Anonymous Monk on Mar 20, 2014 at 00:18 UTC

    Hi, I am trying to use strict perl coding for this simple task, but my variable returns empty. Why?

    Because you're not Coping with Scoping (you're not Lexical scoping like a fox)

    Consider this program, then ask yourself why you do this in your program

    $ perl -le " use warnings; use strict; my $one = 1; { my $one = 2; pri +nt $one; } print $one; " 2 1

    what am I missing?

    Sample input (and sample output) portion of How do I post a question effectively?

Re: Why is my result empty?
by Anonymous Monk on Mar 20, 2014 at 00:20 UTC

    Because my $final_res = $split_final[7]; creates a new variable that is local to the if block, and it hides the other variable named $final_res that you defined before the loop. Write $final_res = $split_final[7]; (remove the my) and you'll only have one variable named $final_res and your code will do what you intend.

    In general, you should use warnings; in addition to use strict; to help you catch some potential problems. Also, take a look at Perl::Critic, which can help you catch this kind of error.

Re: Why is my result empty?
by Marshall (Prior) on Mar 20, 2014 at 05:49 UTC
    Another idea:
    use strict; my $final_res=''; open FILE, $infile; while(my $final_line=<FILE>) { if($final_line=~/^SeqID/) { my $final_line=<FILE>; chomp $final_line; my @split_final=split(/\t/, $final_line); my $final_res = $split_final[7]; $final_res=~s/D/M/g; $final_res=~s/U/M/g; #print $final_res."\n"; } } close FILE; print $final_res."\n"; ################ # different coding ################ use strict; my $infile = ''; #some file open (FILE, "<", $infile) or die "unable to open $infile $!"; while(my $line=<FILE>) { chomp $line; my ($token) = (split(/\t/, $line))[7]; $token=~s/D/M/g; print "Token= ", $token, "\n"; }
Re: OT: Why is my result empty?
by AnomalousMonk (Abbot) on Mar 20, 2014 at 16:27 UTC

    Slightly OT, but if you have a lot of such character-for-character translation to do (a bio-app?), consider using  tr/// instead of  s/// (pattern substitution) for faster operation (see  tr/// in Quote-Like Operators in perlop):

    c:\@Work\Perl\monks>perl -wMstrict -le "my $s = 'xxxDxUxxDDxxUUxDUDxUDUx'; print qq{'$s'}; ;; $s =~ tr/DU/M/; print qq{'$s'}; " 'xxxDxUxxDDxxUUxDUDxUDUx' 'xxxMxMxxMMxxMMxMMMxMMMx'

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