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If I do
`echo $SHELL`
, I get /bin/bash.
But if I try to run this loop:
`for x in {1..20}; do echo $x; done`
I get {1..20} instead of expected 20 numbers.
Maybe ruby uses some other shell to run those commands? How can I work around this?
EDIT: Software versions:
$ irb --version
irb 0.9.5(05/04/13)
$ ruby --version
ruby 1.8.7 (2010-06-23 patchlevel 299) [x86_64-linux]
$ bash --version
GNU bash, version 4.1.5(1)-release (x86_64-pc-linux-gnu)
879
Definition: A subshell is a child process launched by a shell (or shell script). A subshell is a separate instance of the command processor -- the shell that gives you the prompt at the console or in an xterm window.
You can also create subshell by launching new shells from your existing shells. Just run bash and you'll be in a subshell. You can use the exit command to close/exit the shell and move back to the original shell.
When you run a program in your shell, a process is created. This new process is called a child process of the shell. The originating process (the shell from which you ran the command) is called the parent process of the child. When you run a new shell, you are creating a child process under the originating shell.
To make a variable available in a subshell (or any other subprogram of the shell), we have to “export” the variable with the export command.
Ruby uses sh as the subshell for backticks and #system. $SHELL is your default shell, $0 should tell you your current shell. You can get your desired shell by specifically invoking it
$ ruby -v
ruby 1.8.7 (2011-02-18 patchlevel 334) [x86_64-linux], MBARI 0x6770, Ruby Enterprise Edition 2011.03
$ irb --version
irb 0.9.5(05/04/13)
$ irb
irb(main):001:0> `echo $0 -- $SHELL`
=> "sh -- /bin/bash\n"
irb(main):002:0> `bash -c 'echo $0 -- $SHELL'`
=> "bash -- /bin/bash\n"
irb(main):003:0> ENV['SHELL']
=> "/bin/bash"
irb(main):004:0> system 'bash', '-c', 'echo $0 -- $SHELL'
bash -- /bin/bash
=> true
irb(main):005:0> system 'echo $0 -- $SHELL'
sh -- /bin/bash
=> true
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