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How can I generate random numbers in shell scripts?
How can I generate random numbers in shell scripts?This depends on the shell, and the facilities available from the
OS.
a. Some shells have a variable called RANDOM, which evaluates to a
different value every time you dereference it. If your shell has
this variable,
$ number=$RANDOM will produce a random number.
b. Some systems have a /dev/urandom device, which generates a
stream of bits. This can be accessed using the dd(1) utility. An
example of this (from a more extensive discussion of different
techniques at http://www.shelldorado.com/scripts/cmds/rand)
n=`dd if=/dev/urandom bs=1 count=4 2>/dev/null | od -t u4 | \
awk 'NR==1 {print $2}'`
also:
od -vAn -N4 -tu4 < /dev/urandom
c. Use a utility such as awk(1), which has random number generation
included. This approach is the most portable between shells and
operating systems.
awk 'BEGIN {srand();print rand()}'
Note that this doesn't work with older versions of awk. This
requires a version supporting the POSIX spec for srand(). For
example, on Solaris this will not work with /usr/bin/awk, but
will with nawk or /usr/xpg4/bin/awk.
Also, if you call this line more than once within the same
second, you'll get the same number you did the previous time.
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