.\" Copyright (c) 1994-2021 Simon J. Gerraty
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.\" This file is provided in the hope that it will
.\" be of use.  There is absolutely NO WARRANTY.
.\" Permission to copy, redistribute or otherwise
.\" use this file is hereby granted provided that
.\" the above copyright notice and this notice are
.\" left intact.
.\"
.\" Please send copies of changes and bug-fixes to:
.\" sjg@crufty.net
.\"
.Dd January 31, 2024
.Dt DEBUG.SH 8
.Os
.Sh NAME
.Nm debug.sh
.Nd selectively debug scripts
.Sh SYNOPSIS
.Bl -item -compact
.It
.Ic $_DEBUG_SH .\& Pa debug.sh
.Pp
.It
.Ic DebugOn Oo Fl eo Oc Ar tag ...
.It
.Ic DebugOff Oo Fl eo Oc Oo Cm rc= Ns Ar rc Oc Ar tag ...
.It
.Ic Debugging
.It
.Ic DebugEcho Op Ar message
.It
.Ic DebugLog Op Ar message
.It
.Ic DebugShell Ar tag ...
.It
.Ic DebugTrace Ar message
.It
.Ic Debug Ar tag ...
.El
.Sh DESCRIPTION
.Nm
provides the following functions to facilitate flexible
run-time tracing of complicated shell scripts.
.Bl -tag -width 4n
.It Ic DebugOn Oo Fl eo Oc Ar tag ...
turns tracing on if any
.Ar tag
is found in
.Va DEBUG_SH
(a comma separated list of tags).
.Pp
It turns tracing off if
.Ar !tag
is found in
.Va DEBUG_SH .
.Pp
It sets
.Va DEBUG_ON
to the
.Ar tag
that caused tracing to be enabled, or
.Va DEBUG_OFF
if we matched
.Ar !tag .
.Pp
If
.Fl e
option is present, returns 1 if no
.Ar tag
matched.
.Pp
If
.Fl o
option is present, tracing is turned off unless there
was a matched
.Ar tag ,
useful for functions too noisy to tace.
.It Ic DebugOff Oo Fl eo Oc Oo Cm rc= Ns Ar rc Oc Ar tag ...
turns tracing on if any
.Ar tag
matches
.Va DEBUG_OFF
or off if any
.Ar tag
matches
.Va DEBUG_ON .
This allows nested functions to not interfere with each other.
.Pp
The flags
.Fl e
and
.Fl o
are ignored, they just allow for symmetry with calls to
.Fn DebugOn .
.Pp
The optional
.Ar rc
value will be returned rather than the default of 0.
Thus if 
.Fn DebugOff
is the last operation in a function,
.Ar rc
will be the return code of the function.
.It Ic Debugging
returns true if tracing is enabled.
It is useful for bounding complex debug actions, rather than
using lots of
.Ic $DEBUG_DO
lines.
.It Ic DebugEcho
is just shorthand for:
.Bd -literal -offset indent
$DEBUG_DO echo "$@"
.Ed
.It Ic DebugLog Op Ar message
If debugging is enabled, output
.Ar message
prefixed with a time-stamp.
.It Ic DebugShell Ar tag ...
runs an interactive shell if any
.Ar tag
is found in
.Va DEBUG_INTERACTIVE ,
and there is a tty available.
The shell used is defined by
.Va DEBUG_SHELL
or
.Va SHELL
and defaults to
.Pa /bin/sh .
.It Ic DebugTrace Ar message
Debug output can be very noisy, and it can be tricky
to align with the script.
This function outputs a very noticable banner indicating the value of
.Va DEBUG_ON ,
and
.Ar message
is passed to
.Fn DebugLog ,
finally the banner is repeated.
.It Ic Debug Ar tag ...
For backwards compatibility, calls
.Fn DebugOn
and if that does not turn tracing on,
it calls
.Fn DebugOff
to turn it off.
.El
.Pp
The variables
.Va DEBUG_SKIP
and
.Va DEBUG_DO
are set so as to enable/disable code that should be
skipped/run when debugging is turned on.
.Va DEBUGGING
is the same as
.Va DEBUG_SKIP
for backwards compatability and is only set by
.Fn Debug .
.Pp
The use of
.Ic $_DEBUG_SH
is to prevent multiple inclusion,
though it does no harm in this case.
.Sh BUGS
Does not work with some versions of
.Xr ksh 1 .
If a function turns tracing on, ksh turns it off when the
function returns - useless.
.Pp
PD ksh works ok ;-)
.Sh AUTHOR
.An -nosplit
.Nm
was written by
.An Simon J Gerraty Aq Mt sjg@crufty.net .