letter-count.sh

Shall高级编程

#!/bin/bash
# letter-count.sh: Counting letter occurrences in a text file.
# Written by Stefano Palmeri.
# Used in ABS Guide with permission.
# Slightly modified by document author.

MINARGS=2          # Script requires at least two arguments.
E_BADARGS=65
FILE=$1

let LETTERS=$#-1   # How many letters specified (as command-line args).
                   # (Subtract 1 from number of command line args.)


show_help(){
	   echo
           echo Usage: `basename $0` file letters  
           echo Note: `basename $0` arguments are case sensitive.
           echo Example: `basename $0` foobar.txt G n U L i N U x.
	   echo
}

# Checks number of arguments.
if [ $# -lt $MINARGS ]; then
   echo
   echo "Not enough arguments."
   echo
   show_help
   exit $E_BADARGS
fi  


# Checks if file exists.
if [ ! -f $FILE ]; then
    echo "File \"$FILE\" does not exist."
    exit $E_BADARGS
fi



# Counts letter occurrences .
for n in `seq $LETTERS`; do
      shift
      if [[ `echo -n "$1" | wc -c` -eq 1 ]]; then             #  Checks arg.
             echo "$1" -\> `cat $FILE | tr -cd  "$1" | wc -c` #  Counting.
      else
             echo "$1 is not a  single char."
      fi  
done

exit $?

#  This script has exactly the same functionality as letter-count2.sh,
#+ but executes faster.
#  Why?