This `sed` command is performing an in-place text substitution on...

This sed command is performing an in-place text substitution on a file. Let's break it down step by step to understand what it does:

1. sed: The Stream Editor, a Unix command-line utility used for parsing and transforming text.

2. -i: This flag tells sed to edit the file "in place," meaning it modifies the file directly instead of outputting the changes to the terminal or creating a new file.

3. "s% $%%g":

   • s is the substitute command in sed.
   • % is being used as the delimiter instead of the usual /. This is valid in sed and is often used when the pattern contains / to avoid excessive escaping.
   • $ matches a space character ( ) at the end of a line ($ is the anchor for end of line in regex).
   • The second % after $ signifies the replacement part. Since it is empty, it means to remove the matched space.
   • g indicates a "global" replacement, but in this case, it doesn't have any effect because there is only one possible match per line (the space at the end of the line).

4. "$file": Refers to the file being processed. This assumes that the variable $file holds the path to the specific file being modified.

What the code does:

This sed command removes trailing spaces (whitespace at the end of each line) from the file specified in the $file variable. It directly updates the file without creating a backup.

Example:

Suppose the file $file contains the following lines:

Hello world    
This is a test   
Line with no trailing space

After running the command, the file will be updated to:

Hello world
This is a test
Line with no trailing space