Is it possible to make system use bash instead of sh?

W

Wai Tsang

Hi,

Does anyone know if it is possible to use bash instead of sh as the
default shell when "system" is executed?

For example, system("java --version") is executing java --version in sh,
instead of bash, which can be a problem when I tried to do error
redirection.
 
B

Björn Paetzel

Wai said:
Hi,

Does anyone know if it is possible to use bash instead of sh as the
default shell when "system" is executed?

System() should always call /bin/sh (on a POSIX compliant system), but
of course you could still have sh call bash, like this:

system("bash java --version")
 
R

Robert Klemme

System() should always call /bin/sh (on a POSIX compliant system),

Where did you get that information from?
but
of course you could still have sh call bash, like this:

system("bash java --version")

Yes, of course.

robert
 
R

Robert Dober

Hi,

Does anyone know if it is possible to use bash instead of sh as the
default shell when "system" is executed?

For example, system("java --version") is executing java --version in sh,
instead of bash, which can be a problem when I tried to do error
redirection.
If bash is in your path you can do
system("bash -c \"java -version\"")
else you just have to put the full path, this works even on Windows :)

Of course that is not exactly what you want, you would like to tell
Kernel or whatever other object that wants to hear that kind of
message: "You are going to use /bin/bash for system from now on".
So I went digging the code, no such luck, I just could not find the
definition of Kernel#system :(
neither with rb_define_method.*system
nor with def\s*system
and even less with
alias\s*system
or
rb_alias.*system
Hope that somebody more learned will help us out here.

Cheers
Robert
 
B

Brian Candler

Does anyone know if it is possible to use bash instead of sh as the
default shell when "system" is executed?

system() with multiple arguments bypasses the shell. So try:

system("/bin/bash", "-c", "java --version")
 
B

Booker C. Bense

-----BEGIN PGP SIGNED MESSAGE-----

Of course that is not exactly what you want, you would like to tell
Kernel or whatever other object that wants to hear that kind of
message: "You are going to use /bin/bash for system from now on".
So I went digging the code, no such luck, I just could not find the
definition of Kernel#system :(
neither with rb_define_method.*system
nor with def\s*system
and even less with
alias\s*system
or
rb_alias.*system
Hope that somebody more learned will help us out here.

_ Ruby uses the underlying C exec call and any system that does
not use /bin/sh is severely broken. It's part of the POSIX
standard. If you want bash, then use the multi-arg form of the
command which bypasses shell interpretation entirely.

If you want the gory details look in process.c

rb_f_system

_ Booker C. Bense

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fL4OcNifcnM=
=EJLT
-----END PGP SIGNATURE-----
 
A

Ari Brown

Hi,

Does anyone know if it is possible to use bash instead of sh as the
default shell when "system" is executed?
Whenever 'system' is executed? Not sure about that. But what you
might be able to do is have a new file that stores code which defines
'system2', and you could include that. It might be something like:

def system2(command)
system 'bash'
system '#{command}
end

Of course, i have no clue (yet) how to use #{stuff} in my code, so
any help would automatically be worthy of worship.

Oh, and same with having two parameters in 'do' commands. Help? Please?

HTH
-------------------------------------------------------|
~ Ari
crap my sig won't fit
 
G

Gary Wright

Standards like the Single Unix Specification (and the LSB, and so on)
should be used as reasons for standardized behavior in a distributed
OS, but they aren't really relevant to customized installs. If an end
user wants to configure a system differently from the standard, that's
his/her business.

I didn't see anyone claiming differently. I certainly wasn't. I just
perceived the question as a desire for information about the standard.
 

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