Maximum command length in bourne shell


 
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# 1  
Old 10-28-2009
Maximum command length in bourne shell

Hi,

I wanted to know what is the maximum length of command which can be run on a bourne (sh) shell? Where can I find that information? Is it different for different OS flavors?

Please help.

Thanks,

Vineet
# 2  
Old 10-28-2009
Code:
#!/bin/ksh

# The value of the constant ARG_MAX defines how long an argument list your
# kernel can take on the command line before it chokes. Here's a script to
# find out the value of it:

        # Print out the system's architecture
        uname -rms              # or uname -a

        # Let the C preprocessor read in the system's limits from limits.h
        # and then expand the macro ARG_MAX
        # Filter out excess output (there will be some line number information
        # and a gadzillion empty lines)
        #
        # On some gcc systems, I have been unable to find a working cpp.
        # You can use gcc -E - <:<:HERE | tail -1 in that case.

cpp <<HERE | tail -1    # Only the last line is interesting
#include <limits.h>
ARG_MAX
HERE

# 3  
Old 10-28-2009
You can also use getconf:

Code:
getconf ARG_MAX

# 4  
Old 10-28-2009
Quote:
Originally Posted by radoulov
You can also use getconf:

Code:
getconf ARG_MAX

:-)

I started chuckling when I read the cpp solution and half expected to see it followed by a "Why not 'grep ARG_MAX /usr/include/limits.h '?" post.

It's funny how sometimes we use the tools we are most used to - if we use a screwdriver every day, sometimes we'll use the handle end as a hammer.

However, "getconf" isn't always the right tool either because it doesn't necessarily have whatever it is you want. The man page explains what it will know about; and on recent Linuxes you can do "getconf -a". That can help when you aren't sure about whether or not to use a leading underscore or exactly what the constant is called - just

Code:
getconf -a | grep CPUTIME

, for example.

In particular,

Code:
getconf -a | grep MAX

can be educational and enlightening.
# 5  
Old 10-28-2009
Quote:
Originally Posted by TonyLawrence
[...]
However, "getconf" isn't always the right tool either because it doesn't necessarily have whatever it is you want. The man page explains what it will know about; and on recent Linuxes you can do "getconf -a". That can help when you aren't sure about whether or not to use a leading underscore or exactly what the constant is called
[...]
I agree,
most of the time I use grep limits.h ... Smilie
# 6  
Old 10-28-2009
I use "man 5 limits".
# 7  
Old 10-28-2009

Code:
$ man 5 limits
No entry for limits in section 5 of the manual

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