How to use ruby regexp to substitute string with a "callback function"-like manipulation

Question

I have the samples lines, and I want to substitute the leading #s with =s. (The first two lines) But instring.gsub!(/^#+\w/, ""), I can not get the number of # which I want to substitute.

In javascript, I could use a callback function with the replace method, but how could I archive this Ruby?

##Command-line Tool
###Installment
This is a '#'.

The expected result:

==Command-line Tool
===Installment
This is a '#'.

So do you want to replace all the # in your string or only specific occurances? IF you want to replace all the # present, then you could simple do myString.gsub("#", "=") — Mithun Sasidharan
– Mithun Sasidharan, Commented Dec 12, 2011 at 11:35
Not really, only the leading one, and as the leading one varies from one to the other, I need to count them in the substitution. — steveyang
– steveyang, Commented Dec 12, 2011 at 11:48

riffraff · Accepted Answer · 2015-01-05 13:35:06Z

11

a callback block function to the gsub method, probably. I am not sure what you had in mind but could be something like

s.gsub(/^(#+)\w+/) {|m| m.gsub("#", "=") }

edited Jan 5, 2015 at 13:35

answered Dec 12, 2011 at 11:31

riffraff

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2 Comments

steveyang Over a year ago

Thanks, one question. does m means the one match? ?

riffraff Over a year ago

the block argument is the match yes, but in the block, if you want, you can access the perl-ish match variables ($1, $` etc). More infos at ruby-doc.org/core-1.9.3/String.html#method-i-gsub

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