Einstein - cweb

"Change web pages" Shell script.
This script goes through your web pages, changing one string to another string.
Usage like:

 cweb oldstring newstring *html

Usage in lab exam

The usage above is what you want.
But in the lab exam, we have some issues:

For reasons already explained, we need extension .sh
For this test, the program must be called cweb3.
If we do not change the PATH, we suggested you put "./" in front.
So in the lab exam we run it like:
```
 ./cweb3.sh oldstring newstring *html 
```
But that assumes the program is in the same directory as the files. So we make sure that is true for the lab exam.

Debug with Shakespeare files

You need some web pages to change.
Download your own copy of the Shakespeare files.

See how "sed" works

Before even writing the program, first see how "sed" works:

"cd" into the "macbeth" directory in your own copy of the Shakespeare files.
Search for all occurrences of the string "Scotland":
```
 grep Scotland *html 
```
Change "Scotland" to "Kerry" in the output stream by piping the output of grep into sed:
```
 grep Scotland *html | sed -e "s|Scotland|Kerry|g" 
```
This changes the output stream on the command line. It does not change the files.

Modify this script

Here is a script to get started.
Anything in [red brackets] has to be fixed by you.

# Read in the arguments:
OLDSTRING=[first argument]
NEWSTRING=[second argument]

# the following gets rid of the first two arguments
shift
shift

# from now on, "all arguments" means "all arguments from 3rd one on"
# go through all arguments one by one:

for x in [all arguments]
do
 echo "We need to change $OLDSTRING to $NEWSTRING in file $x" 
 ls -l $x 
 echo 
done

As discussed above, for the special lab test environment, we put the program in the same directory as the files.
Go into your macbeth directory. Put the program in here.
Test it with:

./cweb3.sh Scotland Kerry complete.html
./cweb3.sh Scotland Kerry *html

It should just do an "ls" of the files in question, and say what string needs to be changed to what. But not actually change anything.

Test the above locally. Do not move on until this is working.

How to actually change the files

After the "ls -l" in the script, we will insert a line like this:
```
 cat $x | [sed command] > [temporary file]
```
How to construct this line:
- We "cat" the contents of the file.
- Send that via a pipe to "sed" to change one string to another.
- "sed" should change the old string to the new string, whatever they are. It should not be hardwired to change Scotland to Kerry.
- Use double quotes on the sed string, not single quotes - or else variables inside the string are not expanded.
- Then redirect the output to a temporary file.
After this line, use file commands to copy the temporary file back to the original file.
And do another "ls -l" to show the file after it has been changed.

Test the above locally and make sure it works. Do not just try to upload.

Test and upload

In the macbeth directory, search for occurrences of the string "Scotland" in one file:
```
grep Scotland complete.html
```
Change all occurrences of "Scotland" to "Kerry":
```
./cweb3.sh Scotland Kerry complete.html
```
Search for occurrences of "Scotland".
Search for occurrences of "Kerry".
Change all occurrences of "Kerry" back to "Scotland".
Search for occurrences of "Scotland".
Search for occurrences of "Kerry".
When that is working, test with multiple files:
```
./cweb3.sh Scotland Kerry *html
```
When that is working, upload to Einstein for marks.

This script is very useful

Imagine using this script to change one string to another in 1,000 web pages without having to open any editors (or indeed do any work).
In a normal environment, the program can be called anything, can be in your bin directory, it will be in the PATH, and we call it like:

 cweb oldstring newstring *html */*html