I want to remove the middle line from $A. Same as I did with the one liner.

What is desired:

Before: $A="abc\ndef\nghi\n"

After: $B="abc\nghi\n"

You aren't aware of what the switches on your one-liner are doing for you. See perlrun

The -n is the most important one. It applies a while(<>) { ... } loop around your code. So, it is taking your input string, splitting it into lines, assigning each value in turn to $_, and then executing the body of your one-liner for each value. In a program, you have to specify that.

#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

my $A="abc\ndef\nghi\n";
my @list = split /\n/,$A;
while (<@list>) {
  ! /def/ and print
}
[download]

Updated: my most literal attempt didn't work, putting the split inside the while condition. So I use split to create an array. That works better.

Dum Spiro Spero

</quote>You aren't aware of what the switches on your one-liner are doing for you. See perlrun
The -n is the most important one. It applies a while(<>) { ... } loop around your code.
</quote>

You are correct. I am confused as all get out. I think what is getting me the worst is all the short hand and defaults. For instance, is "<>" short hand for "<STDIN>"?.
What would really help me is if you would rewrite

echo -e "abc\ndef\nghi\n" | perl -wlne '! /def/ and print "$_";'

for me with "-we" in place of "-wple" with all the short hand and defaults removed so I could see exactly what is going on. (You would be my hero as I have asked this elsewhere and have not understood it there either. Mostly very helpful folks show me a better way to write it in a full script. And although greatly appreciated, it does not help me understand exactly what is happening in the "-wple" one liner or how to duplicate it in a full script.)

Many thanks, -T

Hello Todd,

Here’s another approach, using the /g modifier in scalar context and relying on the fact that . in a regex matches any character except a newline:

use strict;
use warnings;

my $A = "abc\ndef\nghi\n";

while ($A =~ /(.+)/g)
{
    print "$1\n" unless $1 =~ /def/;
}
[download]

Output:

13:59 >perl 1419_SoPW.pl
abc
ghi

14:00 >
[download]

Hope that helps,

Athanasius <°(((>< contra mundum

Iustus alius egestas vitae, eros Piratica,

I am now able to exclude and reform $B, but I can't do it the other way (include only "def"). Isn't "while" suppose to be the opposite of "until"?

#!/usr/bin/perl

use strict;
use warnings;
use diagnostics;

my $B = "";
my $A = "abc
def
ghi
";

while ( $A =~ m{(.+)}g ) {
   $B .= "$1\n" unless $1 =~ /def/;
}
print "\$B = \n$B\n";


$B = "";
while ( $A =~ m{(.+)}g ) {
   $B .= "$1\n" while $1 =~ /def/;
}
print "\$B = \n$B\n";
[download]

$B =

abc

ghi

Use of uninitialized value $_ in pattern match (m//) at ./ExtractTest.pl line 21 (#1)

Now what am I doing wrong?

I am trying to create a multiline $B from $A. How do I reassemble $B?