Answer to Question #306604 in UNIX/Linux Programming for Mickey

Question

Write a shell program which allows user to add data in a file emp.dat . Allow user to enter data from keyboard. The format for data file is given below

empid: ename: sal: age

If empid exits in a file then do not allow duplicate value to be inserted into file.

Answer 1

#!/bin/bash
# Simple line count example, using bash
#
# Bash tutorial: http://linuxconfig.org/Bash_scripting_Tutorial#8-2-read-file-into-bash-array
# My scripting link: http://www.macs.hw.ac.uk/~hwloidl/docs/index.html#scripting
#
# Usage: ./line_count.sh file
# -----------------------------------------------------------------------------

# Link filedescriptor 10 with stdin
exec 10<&0
# stdin replaced with a file supplied as a first argument
exec < $1
# remember the name of the input file
in=$1

# init
file="current_line.txt"
let count=0

# this while loop iterates over all lines of the file
while read LINE
do
    # increase line counter 
    ((count++))
    # write current line to a tmp file with name $file (not needed for counting)
    echo $LINE > $file
    # this checks the return code of echo (not needed for writing; just for demo)
    if [ $? -ne 0 ] 
     then echo "Error in writing to file ${file}; check its permissions!"
    fi
done

echo "Number of lines: $count"
echo "The last line of the file is: `cat ${file}`"

# Note: You can achieve the same by just using the tool wc like this
echo "Expected number of lines: `wc -l $in`"

# restore stdin from filedescriptor 10
# and close filedescriptor 10
exec 0<&10 10<&-