Find maximum positive integer value in Bourne Shell

Question

I\'m checking a counter in a loop to determine if it\'s larger than some maximum, if specified in an optional parameter. Since it\'s optional, I can either default the maxi

Answer 1

The Bourne shell has no facilities for storing or manipulating numbers - everything is stored as a string. If you are asking about this kind of thing:

if [ $x -gt $y ]

then that is handled by a separate (in the Bourne shell) executable called test, which has a symbolic link called '['. So your question is really about the limits of the test command, which all the docs I can find seem quite reticent about.

Answer 2

I'd stay clear of integer limits as they're non portable and problematic

$ test 123412341234112341235 -gt 1 || echo bash compares ints
-bash: test: 123412341234112341235: integer expression expected
bash compares ints
$ env test 1 -gt 123412341234112341235 || echo coreutils compares strings
coreutils compares strings

Instead I'd just do as you suggest and do the extra comparison like:

[ "$limit" ] && [ $count -gt $limit ]

Answer 3

On my system, the maximum integer of Bash seems to be the same as the LONG_MAX constant of my Perl POSIX library. Obviously, this will vary on your platform, and how your Bash was compiled, etc. But that seems to be a good starting point for testing it:

declare -i max=$(perl -MPOSIX -le 'print LONG_MAX')

echo $max
9223372036854775807

echo "max+1 = " $(( i += 1 ))
max+1 =  -9223372036854775808

uname -a
Linux x200s 3.2.0-33-generic #52-Ubuntu SMP Thu Oct 18 16:29:15 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

Update: After trying this on an old 32 bit Linux, I see that my Perl's POSIX LONG_MAX is 2147483647, but that Bash still has the same limit. It seems to be defined in /usr/include/limits.h, and to depend on your __WORDSIZE, which may be 64 bits even on 32 bit systems :

/* Minimum and maximum values a `signed long int' can hold.  */
#  if __WORDSIZE == 64
#   define LONG_MAX     9223372036854775807L
#  else
#   define LONG_MAX     2147483647L
#  endif