I've been teaching myself Ruby and for a certain problem I'm trying to solve I notice a lot of people are using =~ and /\ in their code. I'm not really sure how they work and would just like an explanation. For example I was looking at someones code for this Pig Latin translator and this is the first time I'm seeing these being used.
def piglatin(word)
if word =~ (/\A[aeiou]/i)
word = word + 'ay'
elsif word =~ (/\A[^aeiou]/i)
match = /\A[^aeiou]/i.match(word)
word = match.post_match + match.to_s + 'ay'
end
word
end
I'm just confused about the /\ slashes and the =~
=~ is known as the "match operator" and can be used to match a string against a regular expression.
The /\ is actually part of two separate things. / denotes the start of a regular expression and \A is known as an "anchor" and is saying "match from the beginning of the string."
edit: This is a link to the documentation that should help you understand more code like you posted.
thank you to Wayne Conrad for a correction on '/\'
=~ is Ruby's pattern-matching operator.
It matches a regular expression on the left to a string on the right.
If a match is found, the index of first match in string is returned. If the string cannot be found, nil will be returned.
/abc/ =~ "abcdef"
In this case, the expression returns 0, because that is the index of the first match of "abc" in the string.
/xyz/ =~ "abcdef"
returns nil because "xyz" cannot be found anywhere in the string.
As for /\:
/ Defines the start and end of a regular expression
\ References a regular expression
For example:
\d => Matches all digits
The equal-tilde operator in Ruby is the “match” operator. It take an regular expression on the left hand side and the string to match on the right hand side. The expression:
/or/ =~ “Hello World”
will return 7 because a match is found on index 7 of the string. The index starts at 0.
The expression:
/abc/ =~ “Hello World”
will return nil because there is no match.
The use of /\A and =~ aside, that code is not written well, so don't emulate it. This is a bit more Ruby-like:
def piglatin(word)
if word[/\A[aeiou]/i]
word + 'ay'
else
word[1..-1] + word[0] + 'ay'
end
end
piglatin('apple') # => "appleay"
piglatin('banana') # => "ananabay"
For this purpose, ^ would have worked as well as \A as they're both "beginning of..." anchors. These are from the Anchors definitions:
^ - Matches beginning of line\A - Matches beginning of string.
