I want to take the value of certain column of a string in perl

I take the value of a row from a txt file and save this in a variable var. I want to take a row of this variable.


#!/usr/bin/perl

use strict;
use warnings;


my $search="/dev/sda1";
my $read_file="Salidaprueba.txt";
my $write_file = "/home/alvaro.andradec/Alvaro.txt";

open (my $WRITE,">> $write_file") or die "can not open the file $write_file";
open(my $READ, $read_file);


while(my $line = <$READ>) {
if ($line =~ /$search/) {
my $var="$line";
chomp($var);
print ("$var\n");

}
}
close $WRITE;
exit;




what the var variable saves is /dev/sda1 4.7G 4.3G 202M 96% /

It has been difficult for me to understand how I take the value and not reach to test the code of a person who left it in this post and then the hidden.

I take the value of a row from a txt file and save this in the variable var. I want to take a row of this string, where is the number 96.


#!/usr/bin/perl

use strict;
use warnings;


my $search="/dev/sda1";
my $read_file="Salidaprueba.txt";
my $write_file = "/home/alvaro.andradec/Alvaro.txt";

open (my $WRITE,">> $write_file") or die "can not open the file $write_file";
open(my $READ, $read_file);


while(my $line = <$READ>) {
if ($line =~ /$search/) {
my $var="$line";
chomp($var);
print ("$var\n");

}
}
close $WRITE;
exit;




I did not understand very well the syntax of regex.
Thanks.

Please place your code snippets inside [CODE]...[/CODE] tags for better readability. You may type those yourself or click the "#" button in the edit controls.

When adding a comment as in your previous posts, please use the Edit button at bottom your posts to make the addition rather than re-posting the entire previous content. This will make it easier for others to follow the thread and understand what you are asking more clearly.

I have read this thread several times and am still not sure that I understand what your question actually is.

What do you mean when you say you want to take the value of a row, and what exactly do you want to do with that value.

If you would post a clearly identified example of the expected input, and a similar clearly stated example of what you expect the output to look like, perhaps we can see clearly what you are trying to accomplish.

My perl skills are rusty so I will defer comment on your code syntax and structure to others.

Originally Posted by andres_fever I take the value of a row from a txt file and save this in the variable var. I want to take a row of this string, where is the number 96. SNIPPED I did not understand very well the syntax of regex. Thanks.

Ok, here is an example for you.

#!/usr/bin/perl

use strict;
use warnings;

# you can group multiple constants together, since constants are represented
# as a hash.
use constant {
    IN_FILE     => 'your_file.txt',
    OUT_FILE    => 'your_out_file.txt'    # you don't seem to be using this.
};

my $search_term = '/dev/sda1';

# please use the three part open.
open my $in_file, '<', IN_FILE or die $!;
chomp(my @lines = <$in_file>);

for my $line (@lines) {
    # using index to find a fixed substring in a string.
    if ( index( $line, $search_term ) >= 0 ) {
        print "$line\n";
        last;
    }

    # using a regular expression. note: please don't use this for fixed patterns.
    if ( $line =~ /$search_term/ ) {
        print "$line\n";
        last;
    }
}

close $in_file;

Originally Posted by individual Ok, here is an example for you. #!/usr/bin/perl use strict; use warnings; # you can group multiple constants together, since constants are represented # as a hash. use constant { IN_FILE => 'your_file.txt', OUT_FILE => 'your_out_file.txt' # you don't seem to be using this. }; my $search_term = '/dev/sda1'; # please use the three part open. open my $in_file, '<', IN_FILE or die $!; chomp(my @lines = <$in_file>); for my $line (@lines) { # using index to find a fixed substring in a string. if ( index( $line, $search_term ) >= 0 ) { print "$line\n"; last; } # using a regular expression. note: please don't use this for fixed patterns. if ( $line =~ /$search_term/ ) { print "$line\n"; last; } } close $in_file;

your script does the same as mine, take the row where the expression is / dev / sda1 4.7G 4.3G 202M 96% /
Now I need to take the number that always accompanies the% sign, since with this is that I can make some calculations of the percentage of free space on a disk

Originally Posted by andres_fever your script does the same as mine, take the row where the expression is / dev / sda1 4.7G 4.3G 202M 96% / Now I need to take the number that always accompanies the% sign, since with this is that I can make some calculations of the percentage of free space on a disk

How do you think you might accomplish that? Any ideas?

Originally Posted by andres_fever your script does the same as mine, take the row where the expression is / dev / sda1 4.7G 4.3G 202M 96% / Now I need to take the number that always accompanies the% sign, since with this is that I can make some calculations of the percentage of free space on a disk

You weren't clear about what you wanted.

#!/usr/bin/perl

use strict;
use warnings;

# you can group multiple constants together, since constants are represented
# as a hash.
use constant {
    IN_FILE  => 'your_file.txt',
    OUT_FILE => 'your_out_file.txt'    # you don't seem to be using this.
};

my $search_term = '/dev/sda1';

# please use the three part open.
open my $in_file, '<', IN_FILE or die $!;
chomp(my @lines = <$in_file>);

for my $line (@lines) {
    # using index to find a fixed substring in a string.
    if (index($line, $search_term) >= 0) {
        for my $col (split ' ', $line) {
            if (rindex($col, '%') >= 0) {
                print $col;
                last;
            }
        }
        last;
    }

    # using a regular expression. note: please don't use this for fixed patterns.
    if ($line =~ /$search_term/) {
        print $line =~ /(\d+%)/;
        last;
    }
}

close $in_file;

Originally Posted by individual You weren't clear about what you wanted. #!/usr/bin/perl use strict; use warnings; # you can group multiple constants together, since constants are represented # as a hash. use constant { IN_FILE => 'your_file.txt', OUT_FILE => 'your_out_file.txt' # you don't seem to be using this. }; my $search_term = '/dev/sda1'; # please use the three part open. open my $in_file, '<', IN_FILE or die $!; chomp(my @lines = <$in_file>); for my $line (@lines) { # using index to find a fixed substring in a string. if (index($line, $search_term) >= 0) { for my $col (split ' ', $line) { if (rindex($col, '%') >= 0) { print $col; last; } } last; } # using a regular expression. note: please don't use this for fixed patterns. if ($line =~ /$search_term/) { print $line =~ /(\d+%)/; last; } } close $in_file;

thank you very much, working with bash I got this easily but with perl it has been difficult for me. If you have books or tutorials that you can provide I would appreciate it. the script worked perfect.

Originally Posted by andres_fever thank you very much, working with bash I got this easily but with perl it has been difficult for me. If you have books or tutorials that you can provide I would appreciate it. the script worked perfect.

You're welcome! Yes it can be confusing, but like anything else practice makes it easier. I'd recommend first typing

perldoc perlintro

in your terminal. If you want to use Perl on the regular, I'd recommened investing in Programming Perl.
EDIT: I forgot to mention, you don't need both versions of selecting the substring in your code. Choose one you like (and that works for you) and remove the other.

You're realy close with $line =~ /$search/ and you can do something like what you want by replacing my $var="$line"; with a similar pattern that is also using a capturing group within it. The specific manual page would be perlre Although that is a reference and not a tutorial it will help to keep checking it, perl patterns in the form of PCRE are used everywhere. Eventually it will become familiar.

I do see lack of simple, to the point examples in the available tutorials however.
Try this one: http://modernperlbooks.com/books/mod...mberedcaptures
That will give you a two-line solution.

Code is read many more times than it is written so the investement needs to be in clear, concise writting. If no one else you are writing to your future self.

you might want to check this: https://perlmaven.com/perl-split

Maybe store % values in an array if you want to process data later

#!/usr/bin/perl

my ($file, @found, $item);

open $file, '<', 'file.txt' or die $!;
@found = grep { /(\d+%)/ and $_ = $1 } <$file>;
close $file;

# @found contains all % values
print 'item '.(++$item).": $_\n" for @found;

Edit: for dealing with df style lines, I think I would rather use split to keep what is associated with the value

#!/usr/bin/perl

my ($file, %found);

open $file, '<', 'file.txt' or die $!;
while (<$file>) {
    next unless /\d+%/;
    my ($disk, $used) = (split ' ')[0,4];
    $found{$disk} = $used;
}

close $file;

# %found hash contains all disk / used values pair
print "$_: $found{$_}\n" for sort keys %found;