backquote and variables

[robertlaferla]

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?

 

[Joel VanderWerf]

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`

 

[Wilson Bilkovich]

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?

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

 

[Joel VanderWerf]

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}`