Recipe – building a frontend with grep

As a finale to this chapter, we will group a few features that we have learned together and build a script that prompts the operator for a filename, a search string, and an operation to carry out with the grep command. We will create the script as $HOME/bin/search.sh, and don't forget to make it executable:

#!/bin/bash 
#Author: @theurbanpenguin 
usage="Usage: search.sh file string operation" 
 
if [ ! $# -eq3 ] ; then 
echo "$usage" 
exit 2 
fi 
 
[ ! -f $1 ] && exit 3 
 
case $3 in 
    [cC]) 
mesg="Counting the matches in $1 of $2" 
opt="-c" 
    ;; 
    [pP]) 
mesg="Print the matches of $2 in $1" 
        opt="" 
    ;; 
    [dD]) 
mesg="Printing all lines but those matching $3 from $1" 
opt="-v" 
    ;; 
    *) echo "Could not evaluate $1 $2 $3";; 
esac 
echo $mesg 
grep $opt $2 $1 

We start by checking for exactly three input arguments using the following code:

if [ ! $# -eq3 ] ; then 
echo "$usage" 
exit 2 
fi 

The next check uses a command...