[ruby-core:45432] [ruby-trunk - Feature #2715] Optimization to avoid spawning shell in Kernel#system call should check for failure conditions

Issue #2715 has been updated by akr (Akira Tanaka).


> As akr-san described, some shells have tail invocation optimization. Thus, even if ruby doesn't have shell invocation optimization, caller can't assume that spawned process is neither child nor grand child.

If we have shell invocation optimization (as now) and the command line is
simple, the command is spawned as a child process.

So removing the optimization breaks a program which assumes this behavior.

For example, IO.popen("foo bar") {|io| ... Process.kill sig, io.pid ... }
will be broken by removing the optimization.

I feel this is incompatible enough.

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Feature #2715: Optimization to avoid spawning shell in Kernel#system call should check for failure conditions
https://bugs.ruby-lang.org/issues/2715#change-27025

Author: taw (Tomasz Wegrzanowski)
Status: Feedback
Priority: Normal
Assignee: akr (Akira Tanaka)
Category: core
Target version: 


=begin
 This is an old issue, I think going all the way back to Perl's system().
 
 Kernel#system is supposed to spawn shell and pass its argument to shell process just like C system(); except it's optimized for a common case of very simple argument, in which case Ruby (like Perl) simply does fork and exec of the string passed, split on whitespace.
 
 This almost works, except shell error reporting is not duplicated. If command doesn't exist, shell would print an error message on stderr, while Ruby like Perl fails silently.
 
 Problem is present in all versions of Ruby including 1.8.7 and 1.9.1.
 
 To reproduce:
 $ ruby -e 'system "fail"'
 $ ruby -e 'system "\"\"fail"'
 sh: fail: command not found
 
 Output of both commands should be identical (or at least close enough, details of error message might differ by Unix flavor).
 
 rb_f_system code for VMS and Windows uses different code paths, so I don't know if it's also affected or not.
 
 I wrote a bit more about background of this issue on my blog: http://t-a-w.blogspot.com/2010/02/what-is-all-this-perl-doing-in-my-ruby.html
=end



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