col-totaler.sh

Shall高级编程

#!/bin/bash

# Adds up a specified column (of numbers) in the target file.

ARGS=2
E_WRONGARGS=65

if [ $# -ne "$ARGS" ] # Check for proper no. of command line args.
then
   echo "Usage: `basename $0` filename column-number"
   exit $E_WRONGARGS
fi

filename=$1
column_number=$2

#  Passing shell variables to the awk part of the script is a bit tricky.
#  One method is to strong-quote the Bash-script variable
#+ within the awk script.
#     $'$BASH_SCRIPT_VAR'
#      ^                ^
#  This is done in the embedded awk script below.
#  See the awk documentation for more details.

# A multi-line awk script is invoked by:  awk ' ..... '


# Begin awk script.
# -----------------------------
awk '

{ total += $'"${column_number}"'
}
END {
     print total
}     

' "$filename"
# -----------------------------
# End awk script.


#   It may not be safe to pass shell variables to an embedded awk script,
#+  so Stephane Chazelas proposes the following alternative:
#   ---------------------------------------
#   awk -v column_number="$column_number" '
#   { total += $column_number
#   }
#   END {
#       print total
#   }' "$filename"
#   ---------------------------------------


exit 0