As you saw in the ‘Hello Ruby World’ script, every script we write will start with
#!/bin/ruby
This isn’t actually part of the ruby language, but is a message to the shell environment telling it what sort of file it’s dealing with and where to find the ruby programme. Let’s move on to the basic syntactic structure of the ruby language itself.
Like many other languages, ruby uses ‘=’ to assign values to variables, and the double equals == to test evaluations. Try this script:
#!/bin/ruby
myAge = 46
puts "You're 46, really?" if myAge == 46
Save it as ‘myAge.rb’ and type ‘ruby myAge.rb’ in Terminal. After verifying that it works, change the second occurrence of ’46’ to ’36’. Save the script and run it again in the Terminal. (Tip: you don’t need to keep typing the script name, just press the UP arrow while Terminal is active and it will fill in the previous command). Note that the script just silently fails because we didn’t tell it what to do if myAge didn’t evaluate to 46.
Let’s just look at that last line again (now corrected back to ’46’)
puts "You're 46, really?" if myAge == 46
This is one way to write a conditional test (ruby heads call this an ‘if modifier’). It’s fine if you have just a simple test, but with more conditions or code, you might want to use the block form:
#!/bin/ruby
myAge = 46
if myAge == 46 then
puts "You're 46, really?"
else
puts "You're not 46, you're 36!"
end
Run the script to check that it works. Now, change line 2 to myAge = 36, save and run again. You should now get the output
"You're not 46, you're 36!"
Ruby also uses something called ‘dot syntax’. Type and save the following script into your text editor, then run it in Terminal and examine the output. Be careful to type it exactly, noting that the word “gimme ” on line 2 has a space between the ‘e’ and the closing quotation mark, and that in the third line, the opening quotation mark is followed by a ‘\’, then an ‘n’ then the word ‘gimme’ with no spaces:
#!/bin/ruby
3.times {print "gimme "}
puts "\ngimme some more"
Hopefully what you see is:
gimme gimme gimme
gimme some more
Let’s just look at how that code works. Although the output is fairly simple, there’s a lot going on here. The second line isn’t, as you might expect, multiplying the number 3, but is actually calling a method .times, whose function is to repeat the code inside the following curly braces exactly the number of times specified by the preceding number. In short calling the method .times on a number n is the same as saying “repeat the following code n times”. Try changing the ‘3’ to another number and see the result. Inside the curly braces we have the command ‘print’, which does the same as ‘puts’ except that it does not move the cursor to a new line after outputting the string. In the final line of code, we start the quoted string with \n. This little character sequence tells the cursor to move to a new line BEFORE the script prints ‘gimme some more’. The cursor also moves to a new line AFTER the output of the string ‘gimme some more’ because we used the command ‘puts’. Try changing ‘puts’ to ‘print’ in the final line and observe the difference. Also notice that you could achieve the same effect as
puts "any old string"
with
print "any old string\n"
To sum up:
= is used to assign values
== is used to test values
. is used to call a method
{ } are used to enclose code
print is used to output a string
\n is used to move the cursor to a new line
puts is used to output a string and move the cursor to a new line at the end
Test Yourself!
Write a script that produces the following output (note you should ensure your script produces a space after the first line):
————————————
I say I say I say
I say
I say
I say
————————————-
See the Answer Here
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