Question

I am calling my programm from perl and getting the output with:

$output = `$calling 2>>bla.txt`;

Now I need just a specific value that will be presented in the output which I can check with Regex.
The needed output is:

Distance from Segment XY to its Centroid is: 3.455564713591596

Where XY is any number, and I just match for the “to its Centroid is: ” the following:

if( $output =~ m/\sto\sits\sCentroid\sis:\s(\d)*$/)

But how do I get only the value that is presented near to the end?
I just want it to be printed on the screen.

Any advice?

Answer 1

You print the number you captured in the regex with the parentheses:

print "$1\n" if ($output =~ m/\sto\sits\sCentroid\sis:\s([-+]?\d*\.?\d+)$/);

You also make sure that the regex can pick up a number with a decimal point, and I’ve allowed an optional sign, too. If you need to worry about optional exponents, add (?:[eE][-+]?\d+)? after the \d+ in my regex.

If you have other things to do with the value, then convert into a regular if statement:

if ($output =~ m/\sto\sits\sCentroid\sis:\s([-+]?\d*\.?\d+)$/)
{
    print "$1\n";
    process_centroid($1);
}