Ruby on Rails script console

I wasn't able to run ./script/console previously, and it used to throw an error since my script console file had included #!/usr/bin/env ruby19. After doing hit and trial I fixed this error by replacing #!/usr/bin/env ruby19 with #!/usr/bin/env ruby.

What does the above line do?

Versions:

• Ruby: 1.9.2-p开发者_开发百科180
• Ruby on Rails: 2.3.5

The #! (hash bang) in the first line of a text file tells the program loader in most *nix systems to invoke the program that is specified next (in this case, /usr/bin/env) with any params supplied (in this case, ruby).

/usr/bin/env is just a portable way of looking in your environment for program named in the first argument. Here it is the Ruby interpreter. If the Ruby interpreter is in your PATH, env will find it and run it using the rest of the file as input.

You probably didn't have a program named ruby19 in your PATH, so you'd get the error. You do have a program named ruby, so that works.

The shebang line in a Unix script is supposed to specify a full path, so this:

#!/usr/local/bin/ruby

is valid but this is not:

#!ruby

The problem with the first form is that, well, you need to use a full path but the actual path won't be the same on all systems. The env utility is often used to allow a script to search the PATH environment variable for the appropriate interpreter, env should always be in /usr/bin/env so you can safely use that as a full path and then let env search the PATH for the named interpreter.

From the fine manual:

env [-i] [name=value]... [utility [argument...]]

The env utility shall obtain the current environment, modify it according to its arguments, then invoke the utility named by the utility operand with the modified environment.

That isn't terribly helpful in your case but I figured I should include it anyway. The shebang use of env is a bit of a hack that doesn't use the intended behavior of env.