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How I can generate random number between 0-60 in sh (/bin/sh, not bash)? This is a satellite box, there is no $RANDOM variable, and other goods [cksum, od (od -vAn -N4 -tu4 < /dev/urandom)].
I want to randomize a crontab job's time.
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To generate random numbers with bash use the $RANDOM internal Bash function. Note that $RANDOM should not be used to generate an encryption key. $RANDOM is generated by using your current process ID (PID) and the current time/date as defined by the number of seconds elapsed since 1970.
$RANDOM is an internal Bash function (not a constant) that returns a pseudorandom integer in the range 0 - 32767. $RANDOM should not be used to generate an encryption key. Example 9-23. Generating random numbers. #!/bin/bash # $RANDOM returns a different random integer at each invocation. #
$$ The process number of the current shell. For shell scripts, this is the process ID under which they are executing.
If you have tr, head and /dev/urandom, you can write this:
tr -cd 0-9 </dev/urandom | head -c 3
Then you have to use the remainder operator to put in 0-60 range.
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How about using the nanoseconds of system time?
date +%N
It isn't like you need cryptographically useful numbers here.
Depending on which version of /bin/sh it is, you may be able to do:
$(( date +%N % 60 ))
If it doesn't support the $(()) syntax, but you have dc, you could try:
dc -e `date +%N`' 60 % p'
Without knowing which operating system, version of /bin/sh or what
tools are available it is hard to come up with a solution guaranteed to work.
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