grep keyword with if-condition

Question

I have an input file with

words;
yadda yadda;
keyword 123;
yadda;

and I want to simply get the value 123 saved as a variable. I tried a solution from here:

my $var;
open(FILE,$data.dat) or die "error on opening $data: $!\n";
while (my $line = <FILE>) {
        if (/^keyword/) {
                $var = $1;
                print $line;
                last;
        }
}
close(FILE);

This isn't working and gives me following error: Use of uninitialized value $_ in pattern match (m//) at ./script.pl line 91, <FILE> line 384. (this occurs for all lines of <FILE>)

I found another solution without the if-condition which just states @string = sort grep /^keyword/,<FILE>; and works. Can you please explain to me what is happening here?

/edit

Thx for the answers and explanations! What do you think is the better/more elegant way? The grep or the if-condition?

Your `grep` question is by and large unrelated, in that it doesn't solve this precise problem. One question per question, please; post a separate question if you still want that answered, as you have already accepted an answer here, and thus marked your problem as solved. — tripleee, Jul 30 '13 at 14:04

tripleee · Answer 1 · 2013-07-30T13:58:08.150

2

$1 refers to the first capture group, but your regex doesn't contain any capture groups, so it's undefined. Try

if ($line =~ /^keyword\s+(-?(?:\d+|\d*\.\d*)(?:[Ee]-?(?:\d+|\d*\.\d*))?)/) {

Notice also that the regex is being applied to the variable containing the line you just read.

Edit: Updated to cope with numbers in scientific notation. This is a significant additional requirement which you should have specified explicitly in the first place.

edited Jul 30 '13 at 13:58

answered Jul 30 '13 at 13:25

tripleee

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This is just working without the `:`. And numbers like 1e-5 gets cut. I also just noticed this following problem right now. – EverythingRightPlace Jul 30 '13 at 13:50

score 2 · Accepted Answer · answered Jul 30 '13 at 13:26

You need the following change:

if ($line =~ m/^keyword\s+(\d+)/)

Explanation: You read into $line, hence $_ which is the default target for match is undefined. In addition, you'd get another error with $1, because your pattern did not specify a capturing group.

grep keyword with if-condition

2 Answers2

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