Default shell for Kernel::system()?

ruby-talk
1

Ist it possible to kind of define a default shell which will be used
for Kernel::system? I often need to invoke from my Ruby scripts
external commands, involving redirection and globbing, for example
(bash syntax)

    foo [a-z]* 2>&-
    bar <<<baz

etc. Since these syntactic elements are shell specific, I need to
specify the shell somehow, for example:

    system("bash --norc -c 'foo [a-z]* 2>&-'")
    system("bash --norc -c 'bar <<<baz'")

which is a bit cumbersome. Of course one obvious solution would be
to define a new function:

    def bash(cmd)
      system("bash --norc -c '"+cmd+"'")
    end

And use instead

    bash('foo [a-z]* 2>&-')
    bash('bar <<<baz')

But this solution has two drawbacks:

First one has to pay special attention that the shell command itself should no contain single quotes. For example, it is all too tempting
to write a call

    bash("my_command 'one argument'")

which looks correct at first sight, but will have a different
effect than

    bash('my_command "one argument"')

due to the interference between Ruby- and bash quoting.

Another drawback of this solution is that one has to include the
definition of the "bash" function with each Ruby script.

So I wonder whether there is may be a simple, builtin solution
for this problem - say, a way to specify the "default shell" used
for system().

Ronald

···

--
Ronald Fischer <ronaldf@eml.cc>
Posted via http://www.newsoffice.de/

2

I'm pretty sure the "default" shell for system is /bin/sh on a *nix.

···

On Aug 1, 2006, at 4:20 AM, Ronald Fischer wrote:

Ist it possible to kind of define a default shell which will be used
for Kernel::system? I often need to invoke from my Ruby scripts
external commands, involving redirection and globbing, for example
(bash syntax)

   foo [a-z]* 2>&-
   bar <<<baz

etc. Since these syntactic elements are shell specific, I need to
specify the shell somehow, for example:

   system("bash --norc -c 'foo [a-z]* 2>&-'")
   system("bash --norc -c 'bar <<<baz'")

which is a bit cumbersome. Of course one obvious solution would be
to define a new function:

   def bash(cmd)
     system("bash --norc -c '"+cmd+"'")
   end

And use instead

   bash('foo [a-z]* 2>&-')
   bash('bar <<<baz')

But this solution has two drawbacks:

First one has to pay special attention that the shell command itself should no contain single quotes. For example, it is all too tempting
to write a call

   bash("my_command 'one argument'")

which looks correct at first sight, but will have a different
effect than

   bash('my_command "one argument"')

due to the interference between Ruby- and bash quoting.

Another drawback of this solution is that one has to include the
definition of the "bash" function with each Ruby script.

So I wonder whether there is may be a simple, builtin solution
for this problem - say, a way to specify the "default shell" used
for system().

Ronald

--
Ronald Fischer <ronaldf@eml.cc>
Posted via http://www.newsoffice.de/

3

Hi,

At Tue, 1 Aug 2006 17:20:25 +0900,
Ronald Fischer wrote in [ruby-talk:205370]:

Ist it possible to kind of define a default shell which will be used
for Kernel::system? I often need to invoke from my Ruby scripts

/bin/sh is hardcoded, like as make, cron and so on.

external commands, involving redirection and globbing, for example
(bash syntax)

    foo [a-z]* 2>&-

Closing descriptor should work on all variants of Bourne shell,
including UNIX Seventh Edition's.

http://www.freebsd.org/cgi/man.cgi?query=sh&apropos=0&sektion=0&manpath=Unix+Seventh+Edition&format=html

       Input output.

       <&- The standard input is closed. Similarly for the standard output
        using >.

       If one of the above is preceded by a digit then the file descriptor
       created is that specified by the digit (instead of the default 0 or 1).
       For example,

      ... 2>&1

       creates file descriptor 2 to be a duplicate of file descriptor 1.

    bar <<<baz

In Ruby, you can:

  IO.popen("bar", "w") {|f| f.puts "baz"}

    def bash(cmd)

        system("bash", "--norc", "-c", cmd)

···

    end

--
Nobu Nakada