Bash – My script produces the same output when using $RANDOM

bashrandom

I am trying to print a random n letter word, where I input n from the command line itself, but for some reason my script is giving me the same answer every time when using the same value for n.

#!/bin/bash                                                                                                                                       
num=$1
egrep "^.{$num}$" /usr/share/dict/words | head -n $RANDOM| tail -n 1

I am calling my script like:

$ bash var3.sh 5
étude             # always the same output when using 5 

$ bash var3.sh 3
zoo               # always the same output when using 3

where var3.sh is the name of my script and 5 is the length of the word I want to print randomly.

How do I get it to print a truly random word?

Best Answer

It doesn't. But $RANDOM returns big numbers (between 0 and 32767) which, especially for words of limited lengths, shows the same result, as the head portion probably returns all the results of the grep (for 3, there are only 819 matches in my /usr/share/dict/words).

Better solution might be to shuffle the results:

egrep "^.{$num}$" /usr/share/dict/words | sort -R | tail -n 1

where -R means --random-sort (a GNU sort extension).

Related Solutions

Bash Path – Refer to a File Under Same Directory of a Script in $PATH

These should work the same, as long as there are no symlinks (in the path expansion or the script itself):

MYDIR="$(dirname "$(realpath "$0")")"
MYDIR="$(dirname "$(which "$0")")"
A two step version of any of the above:

MYSELF="$(realpath "$0")"

MYDIR="${MYSELF%/*}"

If there is a symlink on the way to your script, then which will provide an answer not including resolution of that link. If realpath is not installed by default on your system, you can find it here.

[EDIT]: As it seems that realpath has no advantage over readlink -f suggested by Caleb, it is probably better to use the latter. My timing tests indicate it is actually faster.

Bash – random number needed

See man bash, PARAMETERS section, Shell Variables subsection:

RANDOM Each time this parameter is referenced, a random integer between
       0 and 32767 is generated.  The sequence of random numbers may be
       initialized by assigning a value to RANDOM.  If RANDOM is unset,
       it loses its special properties, even if it is subsequently
       reset.

To restrict the value to the 1..6 interval use the $((RANDOM%6+1)) expression. 1

Or you can use /dev/urandom as follows:

tr -dc '1-6' < /dev/urandom | head -c 1

Best Answer

Related Solutions

Bash Path – Refer to a File Under Same Directory of a Script in $PATH

Bash – random number needed

Related Question