.TH PTRAP 4
.SH NAME
ptrap \-
.IR plumber (4)
filter
.SH SYNOPSIS
.B ptrap
.I port
[\fB!\fR]\fIregexp\fR
[
.I port
[\fB!\fR]\fIregexp\fR ...
]
.SH DESCRIPTION
.I Ptrap
is a program that mounts itself over a
.IR plumber (4)
service mounted at
.B /mnt/plumb
and filters incoming messages according to the rules provided on the command line.
.PP
.I Ptrap
accepts an arbitrary number of argument pairs; each pair consists of a port name
.I port
and a regular expression
.I regexp
(see
.IR regexp (6)).
Each incoming message that does not match
.I regexp
is discarded.
The
.I regexp
can be optionally prefixed by
.B !
to indicate logical inversion (i.e. messages matching the regexp are discarded).
.SH EXAMPLES
Start a 
.IR sam (1)
instance dedicated to editing kernel source code:
.IP
.EX
ptrap edit '^/sys/src/9/'
sam
.EE
.PP
In another window, start a second
.IR sam (1)
instance for all other editing jobs:
.IP
.EX
ptrap edit '!^/sys/src/9/'
sam
.EE
.SH SOURCE
.B /sys/src/cmd/ptrap.c
.SH SEE ALSO
.IR plumber (4),
.IR plumb (6)
.SH BUGS
Multiple filters specified on the same port ignore all but the last one.
.PP
.I Ptrap
would be more useful if it could inhibit sending the message to other clients.
.PP
As far as
.IR plumber (4)
is concerned, even messages dropped by
.I ptrap
are "accepted", which means rules that are supposed to apply to messages not accepted by clients are not invoked (e.g. a rule starting an editor if no one is listening to the
.I edit
port will not work if there is a
.I ptrap
on that port).
.SH HISTORY
.I Ptrap
first appeared in 9front (February, 2018).