Run commands at random

Question

I want to run one of the two commands C1 and C2 at random. How do I do that on commandline (bash)? Will appreciate if a one-liner is possible.

Answer 1

if (( RANDOM % 2 )); then C1; else C2; fi

Answer 2

In your special case:

C$((RANDOM%2+1))

will work :) And hey, it's the shortest answer!

Answer 3

You can do something like this in Bash:

$ (( RANDOM%2 == 0 )) && C1 || C2

This will generate a random number, either 0 or 1. If it's a 0, then C1 runs, otherwise C2 runs if it isn't.

example

$ (( RANDOM%2 == 0 )) && echo 0 || echo 1
1

$ (( RANDOM%2 == 0 )) && echo 0 || echo 1
0

NOTE: The first character, $, is the prompt.

another example

If you're concerned with C1 having to fail so that C2 can run you could restructure the above like so:

(( RANDOM%2 == 0 )) && CMD=C1 || CMD=C2
$CMD

why use this over a if/then statement?

This answer has been criticized a bit but there's a method to my madness. Though this pattern may seem more obscure than a if/then I find it more readable and compact when doing something like the following:

#!/bin/bash
CMD=""
DIRS="/etc /home /www /data1 /data2 /var/log /var/spool/mail"
FILE="/backup/$(hostname)-$(date +'%m-%d-%y').tar.gz"
[ "$1" == "nas" ]  && CMD="lftp -u user,password -e 'cd /dump/; mput /backup/*; quit' nas.mylan.com" || :
[ "$1" == "scp" ]  && CMD="scp /backup/* scponly@dumpserver:incoming' username" || :
[ "$1" == "tape" ] && CMD='tar -cf /dev/st0 /backup/*' || :
[ "$CMD" == "" ]   && exit 1 || :
# make a backup
tar -zcvf  $FILE $DIRS
# Now depend upon circumstances run a backup command
$CMD

References

• Bash shell script tip: Run commands from a variable