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October
20, 2003 -
Useful
Shell Scripting Variables - Part IV -
RANDOM
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RANDOM is a peculiar shell variable, but useful nonetheless.
Peculiar because its value changes
each time it is referenced (yes, this is by
design).
As
you may have already guessed, RANDOM is a
random number generator.
The number generated is an integer
between 0 and 32767, and can come in handy
when writing shell scripts.
To determine if a shell you're
using supports
this variable, the following command can
be used:
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$ print $RANDOM $RANDOM
29302 8082
$
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Two
different numbers will be displayed if
it’s supported, otherwise you will see
nothing.
Assigning
a numeric value to RANDOM prior to
referencing it will initialize (seed) the
sequence of random numbers:
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$ RANDOM=10
$ print $RANDOM
4543
$ print $RANDOM
28214
$ print $RANDOM
11245
$
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This
same sequence of numbers can be repeated
by initializing RANDOM using the same seed:
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$ RANDOM=10
$ print $RANDOM
4543
$ print $RANDOM
28214
$ print $RANDOM
11245
$
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Just
to get you thinking about potential uses for
this handy variable, consider the following...
When writing a shell script to
automate the process of adding new user
accounts, it may be desirable to generate a
unique initial password for each account.
Using the value provided by RANDOM
for all or part of the password would
accomplish this.
It would be wise to use the PID of
the process creating the account(s) to seed
the generator:
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<previous
code>
RANDOM=$$
x=$RANDOM
<subsequent
code>
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Learn
more...
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Tips...
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