This action allows you to list opened files.
p4 command: opened
"List files that are open in pending changelists. Use p4 opened to list files that are currently open via p4 add, p4 edit, p4 delete, or p4 integrate. By default, all open files in the current client workspace are listed. You can use command line arguments to list only those files in a particular pending changelist, or to show open files in all pending changelists, and to limit the number of files displayed."
List opened files in any client workspace (-a) : by default only files in the current workspace will be listed.
Specify changelist number (-c changelist#) : List the files in pending changelist changelist#. To list files in the default changelist, leave this field blank.
Perforce filespec: specify a filespec to limit the files listed which match the filespec
Override Defaults: Override Perforce Global Options