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comp.lang.ruby

irb and single quoted strings

James Byrne

2/5/2009 8:51:00 PM

This is the problem:

irb(main):002:0> x = '--rails --exclude something_is_not_right
\/usr\/lib,test\/lib'
=> "--rails --exclude something_is_not_right \\/usr\\/lib,test\\/lib"

irb(main):004:0> p x
"--rails --exclude something_is_not_right \\/usr\\/lib,test\\/lib"

How do I get a literal string like /usr\/lib,test\/lib into a variable?
Where are these extra '\' artifacts coming from?
--
Posted via http://www.ruby-....
3 Answers

F. Senault

2/5/2009 9:14:00 PM

0

Le 5 février 2009 à 21:50, James Byrne a écrit :

> How do I get a literal string like /usr\/lib,test\/lib into a variable?
> Where are these extra '\' artifacts coming from?

It's just the representation. IRB always shows strings double quoted,
and, in double quotes, a lone \ has to be escaped.

A small example is perhaps more convincing :

22:10 fred@balvenie:~% irb
>> x = '\/usr\/lib'
=> "\\/usr\\/lib"
>> x.length
=> 10
>> '\/usr\/lib' == "\\/usr\\/lib"
=> true

HTH,

Fred
--
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Making sense of all I can
Any time tomorrow I'll pretend to see the light
I just might Shadowman (K's Choice, Shadow Man)

Tim Greer

2/5/2009 9:18:00 PM

0

James Byrne wrote:

> This is the problem:
>
> irb(main):002:0> x = '--rails --exclude something_is_not_right
> \/usr\/lib,test\/lib'
> => "--rails --exclude something_is_not_right \\/usr\\/lib,test\\/lib"
>
> irb(main):004:0> p x
> "--rails --exclude something_is_not_right \\/usr\\/lib,test\\/lib"
>
> How do I get a literal string like /usr\/lib,test\/lib into a
> variable? Where are these extra '\' artifacts coming from?

You have it right, it's just irb that backwacks it in response.

irb(main):004:0> x = '--rails -exclude something_is_not_right
\/usr\/lib,test\/lib'
=> "--rails -exclude something_is_not_right \\/usr\\/lib,test\\/lib"
irb(main):005:0> puts x
--rails -exclude something_is_not_right \/usr\/lib,test\/lib
=> nil
irb(main):006:0>

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Jayce Meade

2/5/2009 9:26:00 PM

0

\ is an escape character for strings. For example, using

a = 'Today is the day, I'm going to New Jersey'

is interpreted as

a = 'Today is the day, I' m going to New Jersey '

This tosses an error because the interpreter assumes the apostrophe in I'm
is the end of the string. The \ escapes that apostrophe so that it's merely
text in the string, not a Ruby operator. The above line would also error out
because 'm', 'going', 'to', 'new', and 'jersey' are unknown methods, and
then also because the last ' was read as the beginning of another string,
causing the string to run to the end of the file and the interpreter yelling
at you because the string wasn't terminated. (In other contexts it would run
until the next occurrence of the ' character, tossing other errors.)

Same thing happens with the backslash.

\ = Escape character
\\ = \ in a string

Example:

irb(main):001:0> puts "c:\documents"
c:documents
=> nil

Here the \ is merely an escape character and thus does nothing since there's
no special characters after it. On the other hand:

irb(main):002:0> puts "c:\\documents"
c:\documents
=> nil

The \\ becomes \ because it used the first backslash as the escape character
for the second backslash.

I hope that helps.

- jayce

--------------------------------------------------
From: "James Byrne" <byrnejb@harte-lyne.ca>
Sent: Thursday, February 05, 2009 12:50 PM
Newsgroups: comp.lang.ruby
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Subject: irb and single quoted strings

> This is the problem:
>
> irb(main):002:0> x = '--rails --exclude something_is_not_right
> \/usr\/lib,test\/lib'
> => "--rails --exclude something_is_not_right \\/usr\\/lib,test\\/lib"
>
> irb(main):004:0> p x
> "--rails --exclude something_is_not_right \\/usr\\/lib,test\\/lib"
>
> How do I get a literal string like /usr\/lib,test\/lib into a variable?
> Where are these extra '\' artifacts coming from?
> --
> Posted via http://www.ruby-....
>
>