The plgrp utility takes one or more space-separated processes or threads as arguments. You can specify processes and threads in a the same syntax that the proc(1) tools use. You can specify a process ID as an integer, with the syntax pid or /proc/pid. You can use shell expansions with the /proc/pid syntax. When you give a process ID alone, the arguments to the plgrp utility include all of the threads of that process.
You can specify a thread explicitly by specifying the process ID and thread ID with the syntax pid/lwpid. You can specify multiple threads of a process by defining ranges with can be selected at once by using the - character to define a range, or with a comma-separated list. To specify threads 1, 2, 7, 8, and 9 of a process whose process ID is pid, use the syntax pid/1,2,7-9.