userland-book/miscellany/mostcommon

#!/usr/bin/env bash

# Optionally specify number of lines to show, defaulting to 10:
TOSHOW=10
CASEOPT=""

while getopts ":in:" opt; do
  case $opt in
    i)
      CASEOPT="-i"
      ;;
    n)
      TOSHOW=$OPTARG
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires an argument." >&2
      exit 1
      ;;
  esac
done

# sort and then uniqify STDIN,
# sort numerically on the first field,
# chop off everything but $TOSHOW lines of input

sort < /dev/stdin | uniq -c $CASEOPT | sort -k1 -nr | head -$TOSHOW