Extract paragraph from multi line string

[yanirdz]

Hi, I have trouble extracting paragraph from multi line string

# the UNIX tool output is a multi line text
my $var = `unix_tool file_name`;

open(FH,'<', \$var) or die "ERROR\n";

$/ = "";
#This is just for example
while (<FH>){
    print "------------------------------------------\n";
    print "$_";
    print "\n";
}

Nothing gets printed. If I don’t use:

$/ = "";

All the lines get printed. And one more thing, If I first save the UNIX tool output file and open it using file handler the code read every paragraph.

[kennethk]

Once I swap my $var = `unix_tool file_name`; to my $var = `cat script.pl`;, I get the expected output. What is unix_tool?

You should be able to split this into two steps (reading in from the backticks followed by the angle-bracket read). What happens when you copy the tool output into a DATA block and use that for your read, i.e.:

#!/usr/bin/perl
use strict;
use warnings;

$/ = "";
#This is just for example
while (<DATA>){
    print "------------------------------------------\n";
    print "$_";
    print "\n";
}
__DATA__
This is the output

From the tool.

Assuming this fails, post the modified snippet (scrubbed if necessary) and we can work from there.

[AnomalousMonk]

One 'problem' with reading input in 'paragrep' mode (i.e.,  $/ = "") is that a seemingly blank line that has any other whitespace in it (e.g.,  "\n \n") is not recognized as being a repeated newline. A repeated newline, and therefor a paragraph break, exactly matches  /\n\n+/ only.

BTW: I get the same printed output from  `cat file` as kennethk.

[jwkrahn]

( my $var = `unix_tool file_name` ) =~ s/(.+?)\n{2,}/-----------------
+-------------------------\n$1\n/sg;

print $var;

[ikegami]

If it prints nothing, you got nothing. Check for errors.

[Krambambuli]

Rephrasing what ikegami said already:

the output of `unix_tool file_name` is probably _empty_.

What if you run this very command in the shell?
What if you use the full path to unix_tool inside the backticks, if unix_tool isn't in the current directory?

Maybe these questions can help you in tracking the problem down.

Update: what if you dump out $var after filling it, like

use Data::Dumper;
print Dumper( $var );

Altough this sounds improbable, maybe you just falled over some bug, maybe one that appears only within your environment: what Perl do you use, on what OS?