Output Percentage of File (Bash code)

I wrote this script recently for a friend in a job who needed to output a certain percentage of a log file, but no more and no less. This was in Linux using bash, so I had a go at writing a solution, which you see below. Posting this up in case it’s useful to anyone else!

 # !/bin/sh # Public Domain, by Neil Grogan 2010 # Script
to output last 30% of file by lines

    OLDFILE="oldlog.txt"
    NEWFILE="newlog.txt"
    PERCENT=0.7

    #Use wc to count lines
    LINES=$(wc -l $OLDFILE | awk '{ print $1}')

    #Linespercent = 2 decimal places, lines by percent, round to whole
    LINESPERCENT=$(echo "scale=2; $LINES*$PERCENT" | bc | xargs printf "%1.0f" )

    # Use tail to get last 30% and output, can use tail -s with sleep time to have it run on sched.
    tail -n $LINESPERCENT $OLDFILE >> $NEWFILE

#programming #bash #code