Perl regex alternation

Question

I have the following strings:

Data 250 MB
Data 1.5 GB
Data 10 GB

I need to capture only the values 250 MB, 1.5 GB, 10 GB. So I wrote the expression

(my $data) = $str1 =~ /Data (\S+ GB|MB)/ or die "$str1\n";

This works for the data in GB, but for MB, I get the result Data 250 MB. Can anyone please explain why?

Answer 1

The alternation operator doesn't operate on words, it means

(\S+ GB) or (MB)

Add non-capturing parentheses:

/Data (\S+ (?:GB|MB))/

which you can further simplify with a character class:

/Data (\S+ [GM]B)/

Answer 2

You defined your capture group as (\S+ GB|MB) which matches \S+ GB or MB (i.e. | is applied to whole capture group).

You want either:

1. /Data (\S+ GB|\S+ MB)/
2. /Data (\S+ (GB|MB))/, or even better /Data (\S+ (?:GB|MB))/, utilizing non-capture group.