TOPIC: Shell Scripts I am working on a 3 part problem and I have successfully co

Question

TOPIC: Shell Scripts

I am working on a 3 part problem and I have successfully completed the first 2 parts but can't figure out the third part for the life of me

Part 3 Question:

Generalize your subst2 script, producing a new script subst that will apply a substitution to any number of files given on the command line. For example

should apply the same substitution throughout each of the three files named there (replaces all occurences of the word "foo" with "bar" in the given files)

This is the code I have that is incorrect:

#!/bin/sh
p1="$1"
shift
p2="$1"
shift

for file in $*
do
if grep "$p1" "$file" > /dev/null;then
mv "$file" "$file.bak"
sed "s/$p1/$p2/g" "$file.bak" > "$file"
fi
done

The error message I get from the professors verification tool reads:

Checking stage 3
grep: king: No such file or directory
grep: king: No such file or directory
grep: mouse.a: No such file or directory
grep: b: No such file or directory

Failed when running: ./subst 'l' 'ww' 'aardvark.cpp' 'bongo.dat' 'cat.dog.bak' 'emu.fish.txt' '../scriptAsst/gecko.cpp' '/home/user/UnixCourse/scriptAsst/hippo.cpp' '/home/user/UnixCourse/scriptAsst/../ibex.txt' 'jay.23' 'king cobra.dat' 'mouse.a b'
A backup file was not created or was mis-named.

Any advice as to why the verification tool doesnt like my answer would be greatly appreciated.

Explanation / Answer

Below is the required script.

#!/bin/bash

find = $1
replace = $2
shift
shift

if [ $# -gt 0 ] ;then
for filename in "$@" ; do
       sed "s/$find/$replace/g" "$filename"
done
fi

Explanation :-
1). Initially the control is on argument1. So, `shift` command forwards the control to next argument.

2). "$@" - It refer to whole of command line text of arguments. Initially it will be below in statement mentioned in question.
foo bar myFile1.txt myFile2.txt myFile3.txt

After using `shift` twice. It will be
myFile1.txt myFile2.txt myFile3.txt

3). Usage of `sed` i pretty clear with the names used.

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