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I'm writing a simple Perl script that translates assembly instruction strings to 32-bit binary code.
I decided to handle translation grouping instruction by type (ADD and SUB are R-Type instructions and so on...) so in my code I'm doing something like this:
my $bin = &r_type($instruction) if $instruction =~ /^(?:add|s(?:ub|lt|gt))\s/;
because I want to handle add, sub, slt and sgt in the same way.
I realized however that maybe using that regular expression could be an 'overkill' for the task I'm supposed to do... could the pattern
/^(?:add|sub|slt|sgt)\s/
represent a better use of regular expressions in this case?
Thanks a lot.
786
* - means "0 or more instances of the preceding regex token"
If a and b are regular expression, a + b is also a regular expression with language {a,b}. If a and b are regular expression, ab (concatenation of a and b) is also regular. If a is regular expression, a* (0 or more times a) is also regular.
Regular expressions are useful in search and replace operations. The typical use case is to look for a sub-string that matches a pattern and replace it with something else. Most APIs using regular expressions allow you to reference capture groups from the search pattern in the replacement string.
Example : The regular expression ab+c will give abc, abbc, abbc, … and so on. The curly braces {…}: It tells the computer to repeat the preceding character (or set of characters) for as many times as the value inside this bracket.
Unless you are using a perl older than 5.10, the simple alternation will perform better anyway (see here), so there is no reason to try to optimize it.
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