SED examples

1. Using back references to append text to each line

To appending the string "EXTRA TEXT" to each line

sed -e 's/\(.*\)/\1EXTRA TEXT/'
   

Note the backslash before the brackets.

\1 is the back reference to the first group (only 1 group in this case, which has matched the whole line.

2. Delete all occurrences of 4 consecutive digits

sed -e 's/[0-9]\{4\}//g'
    

3. Switch or swap 2 words around

sed -e 's/\(.*\)\s\(.*\)/\2 \1/'