I use this method to run an external program:
output=`uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/'`
puts output
ruby will ignore the sed command. Doesn't ruby support "|"?
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Zhao Yi wrote:
I use this method to run an external program:
output=`uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/'`
puts outputruby will ignore the sed command. Doesn't ruby support "|"?
The sed command is not being ignored. The issue is that the backticks (`) do string interpolation before sending the command, which means your backslashes are removed before the commands are sent to the shell.
Take a look at this:
irb(main):001:0> puts `uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/' && ps x | grep uname`
2.6.27.5-desktop-2mnb
24178 pts/8 S+ 0:00 sh -c uname -r | sed 's/([^.]*.[^.]*).*.*/?/' && ps x | grep uname
24182 pts/8 S+ 0:00 grep uname
=> nil
irb(main):002:0> puts system 'uname -r | sed "s/\([^\.]*\.[^\.]*\)\.*.*/\1/" && ps x | grep uname'
2.6
24187 pts/8 S+ 0:00 sh -c uname -r | sed "s/\([^\.]*\.[^\.]*\)\.*.*/\1/" && ps x | grep uname
24191 pts/8 S+ 0:00 grep uname
true
=> nil
irb(main):003:0> puts `uname -r | sed 's/\\([^\\.]*\\.[^\\.]*\\)\\.*.*/\\1/' && ps x | grep uname`
2.6
24201 pts/8 S+ 0:00 sh -c uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/' && ps x | grep uname
24205 pts/8 S+ 0:00 grep uname
=> nil
-Justin
Zhao Yi wrote:
I use this method to run an external program:
output=`uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/'`
puts outputruby will ignore the sed command. Doesn't ruby support "|"?
That's not a smart question.
- Show what happens if you run the same script at the command line
- Show what 'output' actually contains when doing this in Ruby
- Show what version of Ruby you are using, and under what platform
FWIW, it works just fine for me under Ubuntu Hardy with ruby-1.8.6
compiled from source:
$ ruby -v
ruby 1.8.6 (2007-09-24 patchlevel 111) [i486-linux]
$ irb
irb(main):001:0> output=`uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/'`
=> "2.6.24-22-386\n"
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Zhao Yi wrote:
I use this method to run an external program:
output=`uname -r | sed 's/\([^\.]*\.[^\.]*\)\.*.*/\1/'`
puts outputruby will ignore the sed command. Doesn't ruby support "|"?
Instead of strugling with shell-escaping, you can do the regexp part in
Ruby itself:
output = `uname -r`
version = output[ /some-regexp/ ]
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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"
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