Let’s take the linux shadow file as an example. Using sed you can replace the root user password with an empty character.
Suppose your /etc/shadow file look like this:
[root@localhost ~]# cat /etc/shadow root:$6$GE3JYGgDvt5jloXN$l0cNhqsh8564GHsdSgUGz79Cqm2ml.Q0xmtgSDyUVdJRHrgFIWPd0QKB02RedspqunU4yYS0/xDI0fcZgEGt.::0:99999:7:::
You can use the following sed command to replace the root password string between the two semicolon with an empty string.
sed -e 's/root:[[:alnum:]]*[^:]*/root:/g' /etc/shadow
The string [[:alnum:]] in the sed command is a regex that mean : search for any alpha-numeric characters.
Use the -e to test the command before editing your file, to make change permanent use -i in you sed command.