Print format not working

catfish1116 has asked for the wisdom of the Perl Monks concerning the following question:

below is my code:

#!/bin/perl
use v5.10;

  say "Please enter a few lines of text. Press crtl-D when finished";
  @text_lines = <STDIN>;
  chomp($text_lines);
  say "Please enter the width of the column: ";
  $column = <STDIN>;
  $ruler = "1234567890";
  say "$ruler" x $column;

  foreach (@text_lines) {
    #printf "%${column}s\n", $_;
    printf  "%${column}s\n", $_;      
  }
[download]

Here is my output:

Please enter a few lines of text. Press crtl-D when finished

rrrrr eeeeee tyyyyy

Please enter the width of the column: 10 1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890

%10

I copied the code straight out of Learning Perl (7th edition). I typed in 3 lines of text as well as the width I wanted. The output should have been the repeating numbers, (1-0), and then below the text lines with aligned columns, (width called in by <STDIN>. I guess it worked ok for the authors ... not so much for me though .... Any help would be appreciated.

Thanks, Catfish

Comment on Print format not working Download Code

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Re: Print format not working by toolic (Bishop) on Oct 04, 2018 at 17:26 UTC
Tip #1 from the Basic debugging checklist: Use warnings and you will see warning messages. Change: `chomp($text_lines);` [download] to: `chomp(@text_lines);` [download] Also, chomp $column. You should also use strict, in which case you'll need to declare each variable with my.	[reply] [d/l] [select]
Re^2: Print format not working by catfish1116 (Beadle) on Oct 04, 2018 at 18:37 UTC
Declaring the text_lines as my @text_lines & chomping column worked !!! Thank you !! Catfish	[reply]
Re: Print format not working (updated) by AnomalousMonk (Archbishop) on Oct 04, 2018 at 17:35 UTC
`@text_lines = <STDIN>; chomp($text_lines);` [download] The statement `chomp($text_lines);` chomp-s the (nonexistent) scalar `$text_lines` not the `@text_lines` array. Always `use warnings; use strict;` [download] at the start of your scripts. (Update: Actually, it's not accurate to describe `$text_lines` as "nonexistent": if strictures are not enabled (see strict), just referring to such a variable causes Perl to call it into existence. This is known as autovivification (see perlglossary), and such a scalar is initialized with a default value of undef. However, chomp-ing undef doesn't do very much, and the script never accesses `$text_lines` anywhere else, so...) `$column = <STDIN>;` [download] This leaves `$column` un-chomp-ed. `say "$ruler" x $column;` [download] Not sure what this is supposed to do. `rrrrr eeeeee tyyyyy` [download] This is just one line. c:\@Work\Perl\monks>perl -le "use 5.010; ;; use warnings; use strict; ;; say 'Please enter a few lines of text. Press ctrl-Z when finished'; my @text_lines = <STDIN>; chomp(@text_lines); ;; say 'Please enter the width of the column: '; my $column = <STDIN>; chomp $column; ;; my $ruler = '1234567890'; say $ruler x $column; ;; foreach (@text_lines) { printf qq{%${column}s\n}, $_; } " Please enter a few lines of text. Press ctrl-Z when finished xyzzy now is the time for all good men x foo bar ^Z Please enter the width of the column: 7 1234567890123456789012345678901234567890123456789012345678901234567890 xyzzy now is the time for all good men x foo bar [download] (Run under Windoze, so had to use ^Z instead of ^D.) Update: Try `printf qq{%s\n}, $column, $_;` as an experiment (see format specifier in sprintf specifier definitions). (Update: Tried that? Ok, now try `printf qq{%.s\n}, $column, $column, $_;` also.) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]


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