Ruby – Use backticks and system to run Bash or Powershell commands

In ruby you can embed system commands (e.g. bash or Powershell) inside your rb scripts.

The commands that are available depends on whether you are working with a Windows or Linux Operating System.

Windows Operating System

Here’s a script:

irb(main):030:0> `time /t`
=> "12:10\n"                   # Notice that the new line (\n) formatting doesn't get interpreted. 

# There is also the %x(...) which is an alternative to the backtick notation:
irb(main):002:0> %x(time /t)   
=> "14:00\n"

We also have “system” which is slightly different to backtick, in the sense that it returns a boolean (“true” if command as 0-exit-status, and “nil” for all other exit status). However this command also outputs the actual commands output to the standard output.

irb(main):031:0> system("time /t")
12:11
=> true                  # system also outputs a boolean on whether it was succesful. 

# now let's fail on purpose:           
irb(main):032:0> system("timetttt /t")
=> nil

# Now let's capture the output:
irb(main):004:0> result = system("time /t")
14:06
=> true
irb(main):005:0> puts result        
true                   # notice that the result variable only holds the boolean value 
                       # and not the output itself.  
=> nil

The “time /t” comand is actually a cmd command. By default anything passed into backticks/system is assumed to be a windows cmd command. This means a command like “ls” won’t work, instead you have to use the cmd equivalent, whcih is “dir”. The same is true if you try to run any powershell commands, e.g.:

irb(main):005:0> `get-childitem`
Errno::ENOENT: No such file or directory - get-childitem
        from (irb):5:in ``'
        from (irb):5
        from C:/Program Files (x86)/Ruby/Ruby193/bin/irb:12:in `
'
irb(main):006:0> system("get-childitem")
=> nil
irb(main):007:0>

However you can run powershell comands from inside ruby, by prepending your command with “powershell”, like this:

irb(main):014:0> `powershell get-childitem`
=> "\n\n    Directory: C:\\\n\n\nMode                LastWriteTime     Length Name
                                \n----                -------------     ------ ----
                                 \nd----        24/10/2014     11:51            DeployTasks
                                  \nd----        23/04/2014     11:29            GeoWorkspaces
                                   \nd----        15/08/2014     14:50            HashiCorp
                                    \nd----        08/03/2014     11:21            Intel
                                     \nd----        27/06/2014     12:10            IWTemp
                                      \nd----        30/05/2014     12:14            jar
                                       \nd----        16/03/2014     14:52            oracle
                                        \nd----        14/07/2009     04:20            PerfLogs
                                         \nd----        30/05/2014     09:23            Portable-winscp550
                                          \nd----        16/03/2014     12:54            Powershell
                                           \nd-r--        18/07/2014     12:29            Program Files
                                            \nd-r--        12/11/2014     10:32            Program Files (x86)
                                             \nd----        30/05/2014     12:14            PuTTY

irb(main):015:0> system("powershell get-childitem")


    Directory: C:\


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----        24/10/2014     11:51            DeployTasks
d----        23/04/2014     11:29            GeoWorkspaces
d----        15/08/2014     14:50            HashiCorp
d----        08/03/2014     11:21            Intel
d----        27/06/2014     12:10            IWTemp
d----        30/05/2014     12:14            jar
d----        16/03/2014     14:52            oracle
d----        14/07/2009     04:20            PerfLogs
d----        30/05/2014     09:23            Portable-winscp550
d----        16/03/2014     12:54            Powershell
d-r--        18/07/2014     12:29            Program Files
d-r--        12/11/2014     10:32            Program Files (x86)
d----        30/05/2014     12:14            PuTTY



=> true

irb(main):016:0> system("powershell ls")

   Directory: C:\


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----        24/10/2014     11:51            DeployTasks
d----        23/04/2014     11:29            GeoWorkspaces
d----        15/08/2014     14:50            HashiCorp
d----        08/03/2014     11:21            Intel
d----        27/06/2014     12:10            IWTemp
d----        30/05/2014     12:14            jar
d----        16/03/2014     14:52            oracle
d----        14/07/2009     04:20            PerfLogs
d----        30/05/2014     09:23            Portable-winscp550
d----        16/03/2014     12:54            Powershell
d-r--        18/07/2014     12:29            Program Files
d-r--        12/11/2014     10:32            Program Files (x86)
d----        30/05/2014     12:14            PuTTY


=> true
irb(main):017:0>

You can use this approach to also run powershell scripts, i.e.:

PS C:\Temp> cat .\powershell_script.ps1
echo "Hello CodingBee!"
PS C:\Temp> irb
irb(main):001:0> system('powershell -File c:\temp\powershell_script.ps1')  # Note, is single quotes.
Hello CodingBee!
=> true
irb(main):002:0>

Linux

In Linux, you can use the same approach as above. Essentially if a command runs on the bash command line, then it should work from inside ruby.

Here is an example of executing bash commands from inside ruby

By default, the backtick and system approach both outputs the following: