Bash - choose a random line from a file

thomasvs · 11-10-2010, 06:23 AM

cat lines | sort --random-sort | head -n 1

Gives you one random line for the input file lines.

++nick++ · 11-10-2010, 06:28 AM

whatever you do head -n 1 will output the first line??

catkin · 11-10-2010, 07:49 AM

Well, now we've raised Lazarus, an alternative solution

Code:

#!/bin/bash

file=LQ-239334.txt
line_count=$( wc -l < "$file" )
line_index=$(( RANDOM % line_count ))
IFS=$'\n'
lines=( $( cat "$file" ) )
unset IFS
echo "${lines[ line_index ]}"

EDIT: but thomasvs' solution is sweeter

EDIT 2:

And here's an improved version of the script which might run faster than thomasvs' solution, at least for small input files, say less than 4 kB.

Code:

#!/bin/bash

file=LQ-239334.txt
line_count=$( wc -l < "$file" )
line_index=$(( RANDOM % line_count ))
IFS=$'\n'
lines=( $( < "$file" ) )
unset IFS
echo "${lines[ line_index ]}"

brixtoncalling · 12-10-2010, 12:53 AM

Cheers catkin for the latest solution.

See you back in slackware-14.

mikeb1986 · 05-14-2011, 02:48 PM

Sorry to drag up such an old thread, this is just what I wanted

That first script from jmings is great, thanks.

I wonder if someone would expand on one of the scripts, so it displays the word, then when I press return again, it displays the same line but from another text file.
EG, I run it, it displays line 28 from my Japanese vocabulary text file, I press return again and it displays line 28 from the translations text file

Thanks

PTrenholme · 05-14-2011, 03:00 PM

Even simpler: shuf -n 1 <file_name> does it in one command. Try a man -k random | grep '(1' for a list of all stand-alone commands related to random things. (Provided you've installed the man system, which not all distribution default to doing.)