#!/bin/bash
#
# It uses project files and programmer file
# and prints out the name of the programmers who are not assigned to any project
# This script can be invoked
#         % scriptfilename
# Prabu, 6/12/04
#

# trap comand OS_signal_number
# When OS generates the signal_number, the command will be executed
# When a script completes normally, it generates signal 0
#  2> => std error messages of rm command will be redirected to null device
#          i.e. std error message will not be sent to the console
trap "rm ./t[1-5] 2> /dev/null; exit" 0

# cut only the 4th field (project number) of project file
cut -d: -f4 project | sort | uniq > t1
echo
echo ==== output of the first cut command ====
cat t1

# cut only the 1st field (project number) of programmer file
cut -d: -f1 programmer | sort | uniq > t2
echo
echo ==== output of the second cut command ====
cat t2

# -13 => suppress output column1 and column3; display only output column2
comm -13 t1 t2 > t3
echo
echo ==== output of the comm command ====
cat t3

# info coreutils sort
#  +0 => sort according to the zeroth (leftmost) field
#  -1 => output format in single column
sort -t: +0 -1 -o t4 programmer
echo
echo ==== output of the sort command ====
cat t4

# -t: => field delimiter is ':'
# -1 n => join on the nth field of file 1
# -1 1 => join on the 1st (leftmost) field of file 1
# -2 n => join on the nth field of file 2
# -2 1 => join on the 1st (leftmost) field of file 2
# -o 1.3 => output the 3rd field of file1
join -t: -1 1 -2 1 -o 1.3 -o 1.4 -o 1.2 t4 t3 > t5
echo
echo ==== output of the join command ====
cat t5

# -n => suppress output of pattern space
sed -n 's/:/ /gp' < t5
echo
echo ==== output of the sed command ====
cat t5