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Ruby user's guide | Strings |
Ruby deals with strings as well as numerical data. A string may be double-quoted ("...") or single-quoted ('...').
ruby> "abc" "abc" ruby> 'abc' "abc" |
Double- and single-quoting have different effects in some
cases. A double-quoted string allows character escapes by a
leading backslash, and the evaluation of embedded expressions using
#{}
. A single-quoted string does not do this
interpreting; what you see is what you get. Examples:
ruby> print "a\nb\nc","\n" a b c nil ruby> print 'a\nb\n',"\n" a\nb\nc nil ruby> "\n" "\n" ruby> '\n' "\\n" ruby> "\001" "\001" ruby> '\001' "\\001" ruby> "abcd #{5*3} efg" "abcd 15 efg" ruby> var = " abc " " abc " ruby> "1234#{var}5678" "1234 abc 5678" |
Ruby's string handling is smarter and more intuitive than C's. For
instance, you can concatenate strings with +
, and repeat a
string many times with *
:
ruby> "foo" + "bar" "foobar" ruby> "foo" * 2 "foofoo" |
Concatenating strings is much more awkward in C because of the need for explicit memory management:
char *s = malloc(strlen(s1)+strlen(s2)+1); strcpy(s, s1); strcat(s, s2); /* ... */ free(s); |
But using ruby, we do not have to consider the space occupied by a string. We are free from all memory management.
Here are some things you can do with strings.
Concatenation:
ruby> word = "fo" + "o" "foo" |
Repetition:
ruby> word = word * 2 "foofoo" |
Extracting characters (note that characters are integers in ruby):
ruby> word[0] 102 # 102 is ASCII code of `f' ruby> word[-1] 111 # 111 is ASCII code of `o' |
(Negative indices mean offsets from the end of a string, rather than the beginning.)
Extracting substrings:
ruby> herb = "parsley" "parsley" ruby> herb[0,1] "p" ruby> herb[-2,2] "ey" ruby> herb[0..3] "pars" ruby> herb[-5..-2] "rsle" |
Testing for equality:
ruby> "foo" == "foo" true ruby> "foo" == "bar" false |
Note: In ruby 1.0, results of the above are reported in uppercase,
e.g. TRUE
.
Now, let's put some of these features to use. This puzzle is
"guess the word," but perhaps the word "puzzle" is too dignified
for what is to follow ;-)
# save this as guess.rb words = ['foobar', 'baz', 'quux'] secret = words[rand(3)] print "guess? " while guess = STDIN.gets guess.chop! if guess == secret print "You win!\n" break else print "Sorry, you lose.\n" end print "guess? " end print "The word was ", secret, ".\n" |
For now, don't worry too much about the details of this code. Here is what a run of the puzzle program looks like.
% ruby guess.rb guess? foobar Sorry, you lose. guess? quux Sorry, you lose. guess? ^D The word was baz. |
(I should have done a bit better, considering the 1/3 probability of success.)
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