问题
I\'m looking at the documentation for FileUtils. I\'m confused by the following line:
FileUtils.cp %w(cgi.rb complex.rb date.rb), \'/usr/lib/ruby/1.6\'
What does the %w mean? Can you point me to the documentation?
回答1:
%w(foo bar) is a shortcut for ["foo", "bar"]. Meaning it's a notation to write an array of strings separated by spaces instead of commas and without quotes around them. You can find a list of ways of writing literals in zenspider's quickref.
回答2:
I think of %w() as a "word array" - the elements are delimited by spaces and it returns an array of strings.
There are other % literals:
%r()is another way to write a regular expression.%q()is another way to write a single-quoted string (and can be multi-line, which is useful)%Q()gives a double-quoted string%x()is a shell command%i()gives an array of symbols (Ruby >= 2.0.0)%s()turnsfoointo a symbol (:foo)
I don't know any others, but there may be some lurking around in there...
回答3:
There is also %s that allows you to create any symbols, for example:
%s|some words| #Same as :'some words'
%s[other words] #Same as :'other words'
%s_last example_ #Same as :'last example'
Since Ruby 2.0.0 you also have:
%i( a b c ) # => [ :a, :b, :c ]
%i[ a b c ] # => [ :a, :b, :c ]
%i_ a b c _ # => [ :a, :b, :c ]
# etc...
回答4:
%W and %w allow you to create an Array of strings without using quotes and commas.
回答5:
Though it's an old post, the question keep coming up and the answers don't always seem clear to me, so, here's my thoughts:
%w and %W are examples of General Delimited Input types, that relate to Arrays. There are other types that include %q, %Q, %r, %x and %i.
The difference between the upper and lower case version is that it gives us access to the features of single and double quotes. With single quotes and (lowercase) %w, we have no code interpolation (#{someCode}) and a limited range of escape characters that work (\\, \n). With double quotes and (uppercase) %W we do have access to these features.
The delimiter used can be any character, not just the open parenthesis. Play with the examples above to see that in effect.
For a full write up with examples of %w and the full list, escape characters and delimiters, have a look at "Ruby - %w vs %W – secrets revealed!"
回答6:
Instead of %w() we should use %w[]
According to Ruby style guide:
Prefer %w to the literal array syntax when you need an array of words (non-empty strings without spaces and special characters in them). Apply this rule only to arrays with two or more elements.
# bad
STATES = ['draft', 'open', 'closed']
# good
STATES = %w[draft open closed]
Use the braces that are the most appropriate for the various kinds of percent literals.
[] for array literals(%w, %i, %W, %I) as it is aligned with the standard array literals.
# bad
%w(one two three)
%i(one two three)
# good
%w[one two three]
%i[one two three]
For more read here.
回答7:
Excerpted from the documentation for Percent Strings at http://ruby-doc.org/core/doc/syntax/literals_rdoc.html#label-Percent+Strings:
Besides %(...) which creates a String, the % may create other types of object. As with strings, an uppercase letter allows interpolation and escaped characters while a lowercase letter disables them.
These are the types of percent strings in ruby:
...
%w: Array of Strings
回答8:
I was given a bunch of columns from a CSV spreadsheet of full names of users and I needed to keep the formatting, with spaces. The easiest way I found to get them in while using ruby was to do:
names = %( Porter Smith
Jimmy Jones
Ronald Jackson).split('\n')
This highlights that %() creates a string like "Porter Smith\nJimmyJones\nRonald Jackson" and to get the array you split the string on the "\n" ["Porter Smith", "Jimmy Jones", "Ronald Jackson"]
So to answer the OP's original question too, they could have wrote %(cgi\ spaeinfilename.rb;complex.rb;date.rb).split(';') if there happened to be space when you want the space to exist in the final array output.
来源：https://stackoverflow.com/questions/1274675/what-does-warray-mean