Getting the pid of cmd_a in a pipelined command group

[guorzhen]

# Suppose this:
#
#   cmd_a | cmd_b &

Noticed the comment (and the code) about getting the pid of cmd_a, but the rest of the script doesn't seem to make use of it. Anyway, if you still need to get it (more elegantly), here are two other ways:

# Inside cmd_b
PID=$(ps -p $$ -o pgid=)

# or (tested only on cygwin)
PID=$(</proc/$$/pgid)

# Outside cmd_b
# same command with the above, but replace $$ with $!