Recursively chown all files that are owned by a specific user

You can use this portable find command with something like this.

find . -user old-user -exec chown new-user:new-group {} \;

You can expand this to find specific files with -iname options (non POSIX but available on OSX)

find . -iname '*.html' -user www-data -exec chown www-data:www-data {} \;

The . stands for the current folder and below, so you could use a specific path as a base.

find /var/www/ -iname '*.html' -user www-data -exec chown www-data:www-data {} \;

You can use

chown --from=CURRENT_OWNER:CURRENT_GROUP -R new_owner:new_group  *

From the manual chown --help:

  --from=CURRENT_OWNER:CURRENT_GROUP
                     change the owner and/or group of each file only if
                     its current owner and/or group match those specified
                     here.  Either may be omitted, in which case a match
                     is not required for the omitted attribute.

edit: This, of course, only works on linux and most UNIces. For OSX (which is based on BSD) see the solution of @StephenTrapped.

The -h option of chown changes the permission of the symbolic link files themselves and not just the target.

Which could be crucial when doing this on software binary folders, which use symoblic links to switch between versions.

find . -user old-user -exec chown -h new-user:new-group {} \;

Linux answers... To answer the question explicitly:

To only change user owner of this folder and everything within it owned by a specific user:

sudo chown --from=ownerOld -Rc ownerNew  /this_is_my_path/

A few variations to help understanding of syntax which help protect you from catastrophe:

To only change user owner of everything within a folder (not the folder itself) owned by a specific user:

sudo chown --from=ownerOld -Rc ownerNew  /this_is_my_path/*

To only change user owner of this folder and everything within it owned by a specific user & group:

sudo chown --from=ownerOld:groupOld -Rc ownerNew  /this_is_my_path/

To change user & group owners of everything within a folder (not the folder itself) owned by a specific user:

sudo chown --from=ownerOld -Rc ownerNew:groupNew  /this_is_my_path/*

To only change group owners of this folder and everything within it owned by a specific group:

sudo chown --from=:groupOld -Rc :groupNew  /this_is_my_path/

To only change group owners of everything within a folder (not the folder itself) owned by a specific user & group:

sudo chown --from=ownerOld:groupOld -Rc :groupNew  /this_is_my_path/*

do not use the ":" or place the group name if you do not wish the group to change. also you will need to be the owner and have write access so sudo is probably required. Remember this is a dangerous command DO NOT run on root "/" If you get it wrong you are in a world of hurt. Triple check it before you execute it.

switch c is to show changes. switch R is recursive

/path/* will not pick up hidden files.