Shell Programming and Scripting

So guys basically I was really sick and couldn't attend the labs and lectures and I went to my lecture hoping he would say ok I will help you from the start but he just said google it. So If it's possible to make the assignment and explain more in detail why is that would be really helpfull.
I can see that it shouldn't be something complicated so .. any help would be great. Thank you.

Assignment
Write an interactive script that allows a user to change the permissions on an existing
file. The script should ask the user for:
● the full pathname of the file,
● and the octal code specifying the permissions required.
The script should report errors (and abort the program) where:
1. no file pathname is given;
2. the file pathname given does not specify an existing file;
3. no octal code is given;
4. the command to change the permissions fails.
You will need to research the following:
1. echo command for displaying messages;
2. read command for taking user input;
3. if command for checking various conditions (blank input, existence of files,
success/failure of an attempted command, etc.)
4. chmod command for changing permissions;
5. ls -l command for displaying directory entries.
You do not need to do a separate check on the validity of permission codes supplied - let
chmod try to execute and deal with success/failure afterwards.Examples
Here's how some example runs would look. In these examples:
● assume the script is called 'ass1';
● user input is shown in bold;
● the file pathnames in the examples are indicative - they may not exist in your
directories.
A successful run would look something like this:
ass1
Please enter the file pathname: dir/myfile
Please enter the octal permissions code: 744
ass1: File dir/myfile has permissions changed to 744 as shown below:
-rwxr-r-- rothwell staff 4096 Sep 11 2014 dir/myfile
An unsuccessful run would look something like this (error type 2: the file
dir/NOTmyfile does not exist):
ass1
Please enter the file pathname: dir/NOTmyfile
Please enter the octal permissions code: 744
ass1: ERROR: File dir/NOTmyfile does not exist.
ass1: USAGE: Enter the pathname of an existing file.
Another unsuccessful run would look something like this (Error type 4: the
permission code is incorrect):
ass1
Please enter the file pathname: dir/myfile
Please enter the octal permissions code: 784
ass1: ERROR: Failed to change permissions on dir/myfile.
ass1: USAGE: Check that the permission code is valid.
Another unsuccessful run would look something like this (Error type 2: no file
pathname given):
ass1
Please enter the file pathname:
ass1: ERROR: No file pathname given.
ass1: USAGE: Please supply the pathname of an existing file.Notes:
Errors should be echoed to the standard error channel and adhere to the standard syntax
shown in the notes. For example:
echo "${0}: ERROR: No file pathname given." 1>&2
echo "${0}: USAGE: Please supply the pathname of an existing file." 1>&2
exit 1
Which, in an example run, would display on the error channel as:
ass1: ERROR: No file pathname given.
ass1: USAGE: Please supply the pathname of an existing file.
All your exits for errors should be given a unique exit status number in the range 1-255.
Pseudocode for assignment 1:
1. Get pathname of file.
2. If pathname of file is blank exit with error message.
3. If pathname of file given does not name an existing file exit with error message.
4. Get permissions code.
5. If permissions code is blank exit with error message.
6. Attempt to change permissions of file name.
7. If failure to change permissions exit with error message.
8. Otherwise confirm successful change and show file's entry in its directory so that
permissions can be seen by user.

Thead closed...
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