Maximum command length in bourne shell

Shell Programming and Scripting
1

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 
#!/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

You can also use getconf:

getconf ARG_MAX
4

:slight_smile:

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

getconf -a | grep CPUTIME

, for example.

In particular,

getconf -a | grep MAX

can be educational and enlightening.

5

I agree,
most of the time I use grep limits.h ... :slight_smile:

6

I use "man 5 limits".

7 
$ man 5 limits
No entry for limits in section 5 of the manual
8

For my notes, which unix o/s doesn't have "man 5 limits"?

9

None of those I currently have access to:
Linux (Mandriva, Debian), FreeBSD, NetBSD

10

Thanks cfajohnson. I'd assumed that the standard implemention-specific "man 5" pages were pretty universal . After checking a generic Linux "man" site I see that most of the usual ones are present but not necessarily in the the same man section. No mention of "limits" though.
I'll take a closer look at a modern Linux and update my notes.

11

i just figure any script / command that actually needs to parse arguments any where near that limit is so poorly written that it'll fail eventually anyway...