CODEWITHSUNDEEP
rubyshell-exec
mnemotronic
mnemotronic

Reputation: 1026

Ruby different results for "%x{something}" where "something" is quoted or unquoted

I'm using Ruby (2.0) %x{dir} under Windows 7 to run a DOS dir command. The dir being executed is different depending on whether or not dir is quoted.

When the command is bare I get the full output of a DOS dir command:

# sends output of cmd back to program
puts 'run %x{dir}'
puts "dir= " + %x{dir}

What I see on the command line:

run %x{dir}
dir=  Volume in drive C is System
 Volume Serial Number is FFFF-FFFF

 Directory of C:\Users\ ...etc...

08/26/2013  09:16 AM    <DIR>          .
08/26/2013  09:16 AM    <DIR>          ..
01/28/2013  02:28 AM            10,958 AJAX RUG Test.tsc
 ...etc...

When I quote the dir command with either single or double quotes, I get back the output of GnuWin32 dir.exe command which is in the PATH. It took me a while to figure out that the GNU dir was being run. What is causing Ruby to use the dir built into CMD.EXE vs. c:\PROGRA~2\GnuWin32\bin\dir.EXE ???

Also, I've just noticed that my "Pickaxe" and "Ruby Cookbook" use the "%x{}" syntax (BRACES), where the online docs use "%x()" (PARENS) ... is this just a case of general delimiter matching by Ruby?

Upvotes: 2

Views: 245

Answers (1)

Steve Midgley
Steve Midgley

Reputation: 2344

This is a peculiarity of Windows, not Ruby. What's going on is this:

Dir is not an executable but a native function of Windows/cmd.exe. (It's part of cmd.exe - so cmd.exe "traps" when you type dir and runs an internal function rather than looking for "dir.exe" or something out on your file path).

When you put something in quotes in cmd, it forces cmd.exe to look for that command on the path, not via it's internal functions.

You can test this by opening a command prompt in Windows and typing a built-in command (that doesn't exist in gnuwin32) such as copy:

>copy
The syntax of the command is incorrect.

>"copy"
'"copy"' is not recognized as an internal or external command,
operable program or batch file.

If you then create "copy.cmd" file with contents:

echo copy.cmd executed

when you run, you'll see:

>"copy"
copy.cmd executed

Make sense? Basically quoting the command you send to the shell (cmd.exe) from Ruby will cause a different interpretation by cmd.exe - it will prevent internal/built-in cmd.exe commands (such as dir and copy) from working, whereas external utils such as xcopy will work fine.

Upvotes: 2

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