Shell Programming and Scripting

#!/bin/bash
if grep "$1" "$3" > /dev/null; then
mv $3 $3.bak
sed "s/$1/$2/g" $3.bak > $3
fi

For example, putting in 
~/text/subst happy cow myFile1.txt myFile2.txt myFile3.txt

Checking subst...
/home/jzhang/UnixCourse/scriptAsst/subst is not executable.

if [ "$#" -lt 3 ]
then
        echo "usage:  a b file1 file2 ..."
        exit
fi

A="$1"
shift
B="$1"
shift
while [ "$#" -gt 0 ]
do
        echo "substitute $A for $B in $1"
        shift
done

while [ condition ]
do
        something
done

#!/bin/bash
array=( "${@}" )
if [ ${#array} -lt 3 ];then
        echo "Usage:  $0 a b file1 file2 ..."
else
        for (( i=1 ; ++i<${#array}; ));do
                grep  ${array[0]} ${array[i]} > /dev/null && sed -i.bak "s/${array[0]}/${array[1]}/g"  ${array[i]}
        done
fi

#!/bin/bash

array=( "${@}" )
if [ ${#array} -lt 3 ];then
        echo "Usage:  $0 a b file1 file2 ..."
else
        for (( i=1 ; ++i<${#array}; ));do
                grep  ${array[0]} ${array[i]} > /dev/null &&\
                echo "ON FILE  ${array[i]} SUBSTITUTE ${array[0]} FOR ${array[1]} AND BACKUP FILE ${array[i]} TO ${array[i]}.bak" ||\
                echo FILE ${array[i]} UNCHANGED.
                # grep  ${array[0]} ${array[i]} > /dev/null && sed -i.bak "s/${array[0]}/${array[1]}/g"  ${array[i]}
        done
fi

/temp/script happy cow myFile1.txt myFile2.txt myFile3.txt
ON FILE  myFile1.txt SUBSTITUTE happy FOR cow AND BACKUP FILE myFile1.txt TO myFile1.txt.bak
FILE myFile2.txt UNCHANGED.
FILE myFile3.txt UNCHANGED.