Backquote and variables

ruby-talk
1

I am trying to construct a command line to be executed using backquote `` notation. i.e. capturing the output to a string

e.g.

#!/usr/bin/ruby -w
file = "/etc/motd"
string = `"cat " + file`
puts string

% ruby test.rb
sh: line 1: cat : command not found

This doesn't work. It appears that everything between the backquotes is treated as a quoted string. i.e. no variable substitution takes place.

How can I work around this?

2

robertlaferla@comcast.net wrote:

I am trying to construct a command line to be executed using backquote `` notation. i.e. capturing the output to a string

e.g.

#!/usr/bin/ruby -w
file = "/etc/motd"
string = `"cat " + file`

string = `#{"cat "} + file`

···

puts string

% ruby test.rb
sh: line 1: cat : command not found

This doesn't work. It appears that everything between the backquotes is treated as a quoted string. i.e. no variable substitution takes place.

How can I work around this?

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

3

The backtick string is treated like a double-quote. Therefore, you can do this:
file = '/etc/motd'
motd = `cat #{file}`
puts motd

···

On 10/24/06, robertlaferla@comcast.net <robertlaferla@comcast.net> wrote:

I am trying to construct a command line to be executed using backquote `` notation. i.e. capturing the output to a string

e.g.

#!/usr/bin/ruby -w
file = "/etc/motd"
string = `"cat " + file`
puts string

% ruby test.rb
sh: line 1: cat : command not found

This doesn't work. It appears that everything between the backquotes is treated as a quoted string. i.e. no variable substitution takes place.

How can I work around this?

4

Joel VanderWerf wrote:

I am trying to construct a command line to be executed using backquote `` notation. i.e. capturing the output to a string

e.g.

#!/usr/bin/ruby -w
file = "/etc/motd"
string = `"cat " + file`

string = `#{"cat "} + file`

Oops, I didn't really read your example. I assumed you were trying to get the command name interpolated in the string. Wilson answered your question.

If you wanted to interpolate both, you could do this:

cmd="cat"
file="/etc/motd"
motd = `#{cmd} #{file}`

···

robertlaferla@comcast.net wrote:

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407