In a file test.txt I have the following text line
COPYRIGHT (c) 2020 alex4200
in which I want to use sed to find that line and to replace the year 2020 by the year 2021. I have tried the following expression:
sed -i -E "s/COPYRIGHT .*(\d\{4\}) alex4200/2021/" test.txt
but it did not change the text in the file test.txt. What am I missing?
First thing first \d is not supported in sed you need to use [0-9]. Then your expression is also not correct(even you fix \d it will not work with your tried code), so I have corrected it as per your shown samples. With your shown samples, please try following.
sed -E 's/^([^ ]* +[^ ]*) +([^\s]*) +(.*)$/\1 2021 \3/' Input_file
Once you are happy with results(which will be shown on terminal) you can use -i option to do inplace save in above code.
Explanation: Simple explanation would be, using sed's backreference capability while substitution. In first part of substitution part, making 3 back references as per shown samples, where 2nd back reference will have 2020 value in it, while doing substitution putting 2021 value there.
Explanation of regex:
^([^ ]* +[^ ]*) ##From starting of value creating 1st back reference which will match values just before 2nd occurrence of space.
+ ##Matching 1 or more occurrences of spaces here.
([^\s]*) ##Creating 2nd capturing group which will match everything till space comes, to catch 2020 basically.
+ ##Matching 1 or more occurrences of spaces here.
(.*)$ ##Matching everything till last here and creating 3rd back reference here.
Fixing OP's attempts:
sed -E 's/^(COPYRIGHT .*\(c\))\s+([^ ]*)\s+(.*)/\1 2021 \3/' Input_file
OR to match digits with shown samples, following could be used:
sed -E 's/^(COPYRIGHT\s+\(.*\))\s+([0-9]{4})(.*)$/\1 2021 \3/' Input_file