#!/bin/bash
# wf.sh: Crude word frequency analysis on a text file.
# This is a more efficient version of the "wf2.sh" script.


# Check for input file on command line.
ARGS=1
E_BADARGS=65
E_NOFILE=66

if [ $# -ne "$ARGS" ]  # Correct number of arguments passed to script?
then
  echo "Usage: `basename $0` filename"
  exit $E_BADARGS
fi

if [ ! -f "$1" ]       # Check if file exists.
then
  echo "File \"$1\" does not exist."
  exit $E_NOFILE
fi



########################################################
# main ()
sed -e 's/\.//g'  -e 's/\,//g' -e 's/ /\
/g' "$1" | tr 'A-Z' 'a-z' | sort | uniq -c | sort -nr
#                           =========================
#                            Frequency of occurrence

#  Filter out periods and commas, and
#+ change space between words to linefeed,
#+ then shift characters to lowercase, and
#+ finally prefix occurrence count and sort numerically.

#  Arun Giridhar suggests modifying the above to:
#  . . . | sort | uniq -c | sort +1 [-f] | sort +0 -nr
#  This adds a secondary sort key, so instances of
#+ equal occurrence are sorted alphabetically.
#  As he explains it:
#  "This is effectively a radix sort, first on the
#+ least significant column
#+ (word or string, optionally case-insensitive)
#+ and last on the most significant column (frequency)."
#
#  As Frank Wang explains, the above is equivalent to
#+       . . . | sort | uniq -c | sort +0 -nr
#+ and the following also works:
#+       . . . | sort | uniq -c | sort -k1nr -k
########################################################

exit 0

# Exercises:
# ---------
# 1) Add 'sed' commands to filter out other punctuation,
#+   such as semicolons.
# 2) Modify the script to also filter out multiple spaces and
#+   other whitespace.