Command to remove a ssh authorized key on server

sed provides a compact solution:

sed -i.bak '/REGEX_MATCHING_KEY/d' ~/.ssh/authorized_keys

This will save the original authorized_keys in authorized_keys.bak. If you don't want the backup then just change -i.bak to -i.

You can even remove multiple keys:

sed -i.bak '/REGEX1/d; /REGEX2/d' ~/.ssh/authorized_keys

The only tricky bit here is special characters in the regex need to be escaped.

As Ignatio suggested this can be done with grep -v.

Here is a example which removes the key containing some unique string or just deletes the authorized_keys file when no other key remains.

if test -f $HOME/.ssh/authorized_keys; then
  if grep -v "some unique string" $HOME/.ssh/authorized_keys > $HOME/.ssh/tmp; then
    cat $HOME/.ssh/tmp > $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp;
  else
    rm $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp;
  fi;
fi

Replace some unique string with something that only exists in the key you wish to remove.

As a oneliner over ssh this becomes

ssh hostname 'if test -f $HOME/.ssh/authorized_keys; then if grep -v "some unique string" $HOME/.ssh/authorized_keys > $HOME/.ssh/tmp; then cat $HOME/.ssh/tmp > $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp; else rm $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp; fi; fi'

Tested on Linux (SLES) and HP-UX.

Nope. You'll need to SSH in and use sed or grep to remove the key from the file.