From: Brian Candler <b.candler@...>
Date: 2009-01-07T22:03:35+09:00
Subject: Re: A question about running external program

Justin Collins wrote:
> irb(main):003:0> puts `uname -r | sed
> 's/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\1/' && ps x | grep uname`

I think that's not quite right, because \\1 is still converted into a 
single character with ASCII code 1, rather than being passed to sed as 
\1

irb(main):013:0> `echo 's/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\1/'`
=> "s/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\001/\n"

So as far as I can see, you need to use \\\\1 to get a literal \ 
followed by 1

irb(main):014:0> `echo 's/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\\\1/'`
=> "s/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\1/\n"

Escapes like \. and \( are OK, but for consistency you can escape them 
all in the same way:

irb(main):015:0> `echo 
's/\\\\([^\\\\.]*\\\\.[^\\\\.]*\\\\)\\\\.*.*/\\\\1/'`
=> "s/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\1/\n"
-- 
Posted via http://www.ruby-forum.com/.