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Re: why won't is print every value???

by Util (Priest)
on Jun 06, 2002 at 00:03 UTC ( [id://172050]=note: print w/replies, xml ) Need Help??


in reply to why won't is print every value???

Util meditates on:
"If I put the whole thing into the loop i end up asking the same question over and over to the user."


Yes. This will anger your users.

Where should Anonymous Monk request the user's input? Before, during, or after the while(<INFILE>){} loop?
For clarity below, I will set aside strict, /pattern/oi, chomp, and similar elements of our craft.

During:
while (<INFILE>) { $word = <STDIN>; print if /$word/; } # Officiate is asked for input on every line of the file. # Officiate throttles monk; blacking out, you meditate on your error.
After:
while (<INFILE>) { $line = $_; } my $word = <STDIN>; print $line if $line =~ /$word/; # $line only contains the last line of the file! # Officiate makes bad decision based on wrong output. # Monk goes hungry.
After (fixed):
while (<INFILE>) { push @lines, $_; } $word = <STDIN>; foreach (@lines) { print if /$word/; } # File data is stored until $word is known. # Officiate gets correct output, is pleased while file is small. # Monk is thrashed when the disk thrashes on a large file.
Before:
$word = <STDIN>; while (<INFILE>) { print if /$word/; } # There is no need to store the file data. # Harmony is achieved.

Util comes out of Monk Funk, enters Homework Mode
Practical notes on Anonymous Monk's posted code:

  • The first field in an array is $array[0], not $array[1].
  • eq is for string comparisons. Use == for numbers.
  • $self="something\n"; print "$self\n"; yields two newlines per line.

FWIW, here is how I would do this sort of thing in the real world. No huge files, @types dynamically calculated. Code tested.

#!/usr/bin/perl -W use warnings 'all'; use strict; # Scans the input file(s), breaking each line into fields. # Builds a key from prettified $type, and stores an array of # output lines in a hash under the key. Prints a list of all # the types seen in the file(s), and asks the user to choose one. # Prints the output lines stored for that key/type. my $limit = 30; my $usage = "Usage: $0 infile\n"; die $usage unless @ARGV; sub pretty { return ucfirst lc shift } my %lines; while (<>) { my ($whatever, $type, $num) = split; my $key = pretty($type); push @{ $lines{$key} }, "$type\t$num\n" if $num < $limit; } my @types = sort keys %lines; my $ask = "Please select a category:\n"; $ask .= "\t$_. $types[$_]\n" foreach 0 .. $#types; my $type; while (not $type) { print $ask; chomp(my $choice = <STDIN>); $type = $types[$choice] or print "$choice was not an option!\n" and +next; } my $key = pretty($type); print @{ $lines{$key} };

Clearly, Util is suffering from Perl Golf induced dementia.
Waits to get slammed with "Deprecated use of 'officiate'" error.

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