\cfg{man-identity}{buildrun}{1}{2012-08-01}{Simon Tatham}{Simon Tatham}

\title Man page for \cw{buildrun}

\U NAME

\cw{buildrun} - run one program after another has completed successfully

\U SYNOPSIS

\c buildrun -w control-directory   command1 [ argument... ]
\e bbbbbbbb bb iiiiiiiiiiiiiiiii   iiiiiiii   iiiiiiii
\c buildrun -r control-directory [ command2 [ argument... ] ]
\e bbbbbbbb bb iiiiiiiiiiiiiiiii   iiiiiiii   iiiiiiii

\U DESCRIPTION

\cw{buildrun} is a utility which you can use to wrap two separate
commands, and it will wait to run the second command until the first
command is not currently running and its last run completed
successfully. This includes waiting while the first one runs several
times (if the first few runs fail), and also includes not waiting at
all if it's \e{already} true that the most recent run of the first
command was successful.

You might use \cw{buildrun} in situations where you want to run two
commands in succession, but (for one reason or another) you'd rather
have them run in separate shell sessions and therefore you don't want
to take the obvious approach of simply issuing a compound command
using the shell's \cw{&&} operator.

A typical scenario involves the first command being a software build
process (a compile command, or \cw{make}, or similar), and the second
being some attempt to run the resulting program or its test suite or a
debugger. You might want to run your build and test commands in
separate shell sessions for several reasons: if it's convenient to
give them different working directories, or in order to separate the
shell command-recall histories (so that the build terminal has all the
commands related to editing and searching source files, and the test
terminal has the ones related to adjusting the test environment), or
in order to separate their output (so that successive test runs appear
adjacent to each other in the test terminal and can be easily
compared, while the output from build commands is available for
checking if it's needed but doesn't keep scrolling the test output off
the screen).

To use \cw{buildrun}, you must first decide on a location for a
\e{control directory} which the two \cw{buildrun} processes can use to
communicate between themselves. Then, in one window, you run the
command you want to run first (e.g. the compile operation), prefixed
with a \cw{buildrun -w} command giving the pathname of the control
directory. For instance, you might run

\c buildrun -w /tmp/controldir make
\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

Then, in another window, run the second command (e.g. a test or
debugging command) prefixed with a similar \cw{buildrun -r} command,
for example

\c buildrun -r /tmp/controldir ./test.sh
\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

The instance of \cw{buildrun} run with \cw{-w} will immediately run
its command; the instance run with \cw{-r} will wait for the \cw{-w}
command to complete, and then run its own command. If the first
command fails, the \cw{buildrun -r} process will continue to sleep;
you can then correct the problem and re-run the compile, and
\cw{buildrun -r} will only wake up once an instance of \cw{buildrun
-w}'s command completes successfully.

If you then immediately re-run \cw{buildrun -r} without starting
another build, it will run its command instantly without waiting. So
you can repeat your testing or debugging, or run several different
test runs, by simply recalling the same test command \e{including} the
\cw{buildrun -r} prefix.

(The option names \cw{-w} and \cw{-r} are intended to imply that the
first command is writing some kind of resource, such as a compiled
program or data file, and that the second command intends to read that
resource and hence needs the first command to have written it
correctly.)

\U OPTIONS

You must specify one of \cw{-w} and \cw{-r}.

\dt \cw{-w}

\dd Runs \cw{buildrun} in write mode. You must provide a command line;
\cw{buildrun -w} will run that command, and use the control directory
to signal to any waiting \cw{buildrun -r} instances when it has
completed successfully.

\dt \cw{-r}

\dd Runs \cw{buildrun} in read mode. If a command wrapped by
\cw{buildrun -w} is currently in progress, or if the last such command
failed, then \cw{buildrun -r} will wait until one succeeds before
doing anything. However, if no \cw{buildrun -w} is currently running
and the last one completed successfully, \cw{buildrun -r} will not
wait at all.

\lcont{

If a command line is provided, \cw{buildrun -r} will run that command
after it finishes waiting. If no command line is provided,
\cw{buildrun -r} will simply return success when it finishes waiting.

}

\U ARGUMENTS

\dt \e{control-directory}

\dd This argument is mandatory in both \cw{-w} and \cw{-r} modes. It
must give the pathname of a directory which the two instances of
\cw{buildrun} will use to communicate with each other.

\lcont{

You need not create the control directory; \cw{buildrun -w} will
create it the first time it runs. It will also be deleted every time
\cw{buildrun -w}'s command completes successfully, because that's how
success is communicated to \cw{buildrun -r}. (A side effect of that is
that if \cw{buildrun -r} is run before \e{ever} running \cw{buildrun
-w}, it will behave as if there had been a successful \cw{-w} run.)

The control directory should not be on a network-mounted filesystem,
since network filesystems sometimes diverge from the normal Unix
behaviour which \cw{buildrun} relies on. Using a directory in
\cw{/tmp} is recommended.

Of course, instances of \cw{buildrun} using different control
directories will be completely independent of each other. So you can
simultaneously run two or more pairs of commands each linked by their
own pair of \cw{buildrun}s, and as long as each pair has a separaet
control directory, they won't interfere with each other.

}

\dt \e{command} (and optional arguments)

\dd The first word on \cw{buildrun}'s command line which is not an
option or the control directory name will be treated as a command to
be run by \cw{buildrun}, and anything following that word will be
treated as arguments to that command. The command will be run directly
using the \cw{execvp}(\e{3}) function, so shell syntax (pipes,
redirections etc) is not supported. If you need your command to
contain things like that, you can achieve it by explicitly invoking a
shell, e.g.

\lcont{

\c buildrun -w sh -c '(cmd1; cmd2 | cmd3) > outfile'
\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

In \cw{buildrun -r} mode, an alternative to doing that is simply not
to provide a command at all, and instead tell your shell to run a
complex command \e{after} \cw{buildrun}, e.g.

\c buildrun -r && (cmd1; cmd2 | cmd3) > outfile
\e bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

(This alternative is not available with \cw{buildrun -w}, since that
has to run its command as a subprocess so that it can wait for it to
finish and see whether it worked.)

}

\U LICENCE

\cw{buildrun} is free software, distributed under the MIT licence.
Type \cw{buildrun --licence} to see the full licence text.

\versionid $Id$