223 lines
7.4 KiB
Markdown
223 lines
7.4 KiB
Markdown
% redo(1) Redo 0.00
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% Avery Pennarun <apenwarr@gmail.com>
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% 2010-12-12
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# NAME
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redo - rebuild target files when source files have changed
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# SYNOPSIS
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redo [options...] [targets...]
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# DESCRIPTION
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redo is a simple yet powerful tool for rebuilding target
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files, and any of their dependencies, based on a set of
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rules. The rules are encoded in simple `sh`(1) scripts
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called '.do scripts.'
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redo supports GNU `make`(1)-style parallel builds using the
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`-j` option; in fact, redo's parallel jobserver is compatible
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with GNU Make, so redo and make can share build tokens with
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each other. redo can call a sub-make (eg. to build a
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subproject that uses Makefiles) or vice versa (eg. if a
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make-based project needs to build a redo-based subproject).
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Unlike make, redo does not have any special syntax of its
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own; each *target* is built by running a .do file, which is
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simply a shell script that redo executes for you with a
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particular environment and command-line arguments.
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If no *targets* are specified, redo pretends you specified
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exactly one target named `all`.
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Note that redo *always* rebuilds the given targets
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(although it may skip rebuilding the targets' dependencies
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if they are up to date). If you only want to rebuild
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targets that are not up to date, use `redo-ifchange`(1)
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instead.
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A .do script can call redo recursively to build its
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dependencies.
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# OPTIONS
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-j, --jobs=*maxjobs*
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: execute at most *maxjobs* .do scripts in parallel. The
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default value is 1.
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-d, --debug
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: print dependency checks as they happen. You can use
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this to figure out why a particular target is/isn't being
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rebuilt when your .do script calls it using
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`redo-ifchange`.
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-v, --verbose
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: pass the -v option to /bin/sh when executing scripts.
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This normally causes the shell to echo the .do script lines
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to stderr as it reads them. Most shells will print the
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exact source line (eg. `echo $3`) and not the
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substituted value of variables (eg. `echo
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mytarget.redo.tmp`).
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-x, --xtrace
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: pass the -x option to /bin/sh when executing scripts.
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This normally causes the shell to echo exactly which
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commands are being executed. Most shells will print
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the substituted variables (eg. `echo
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mytarget.redo.tmp`) and not the original source line
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(eg. `echo $3`).
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-k, --keep-going
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: keep building as many targets as possible even if some
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of them return an error. If one target fails, any
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target that depends on it also cannot be built, of course.
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--shuffle
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: randomize the order in which requested targets are
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built. Normally, if you run `redo a b c`, the targets
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will be built exactly in that order: first `a`, then
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`b`, then `c`. But if you use `-j`, they might end up
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being built in parallel, so it isn't safe to rely on
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this precise ordering. Using `--shuffle`, redo will
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build its targets in random order even without `-j`,
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which makes it easier to find accidental dependency
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problems of this sort. NOTE: if you really just want
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to guarantee that `a` is built, then `b`, then `c`, you
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can just run three `redo` commands consecutively.
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Because your .do script is just a script, it will not
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be accidentally parallelized.
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--debug-locks
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: print messages about acquiring, releasing, and waiting
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on locks. Because redo can be highly parallelized,
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one instance may end up waiting for a target to be
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built by some other instance before it can continue.
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If you suspect this is causing troubles, use this
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option to see which instance is waiting and when.
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--debug-pids
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: add the process id of the particular redo instance to each
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output message. This makes it easier to figure out
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which sub-instance of redo is doing what.
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# DISCUSSION
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The core of redo is extremely simple. When you type `redo
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targetname`, then it will search for a matching .do file
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based on a simple algorithm. For example, given a target
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named `mytarget.a.b.c.d`, redo will look for a .do file in
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the following order:
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- mytarget.a.b.c.d.do
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- default.a.b.c.d.do
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- default.b.c.d.do
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- default.c.d.do
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- default.d.do
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- default.do
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In all cases, the .do file must be in the same directory as
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the target file.
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The first matching .do file is executed as a `/bin/sh`
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script. The .do script is always executed with the current
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working directory set to the directory containing the .do
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file (and thus the target). Because of that rule, the
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following two commands always have exactly identical
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behaviour:
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redo path/to/target
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cd path/to && redo target
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(Note: in `make`(1), these commands have confusingly
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different semantics. The first command would look for a
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target named `path/to/target` in `./Makefile`, while the
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second command would look for a target named `target` in
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`./path/to/Makefile`. The two Makefiles might give
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completely different results, and it's likely that the
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first command would have incomplete dependency information.
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redo does not have this problem.)
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The three arguments passed to the .do script are:
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- $1: the basename of the target (eg. mytarget.a.b)
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- $2: the extension of the target, if any (eg. .c.d)
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- $3: a temporary filename that the .do script should write
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its output to.
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Instead of using $3, the .do script may also write the
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produced data to stdout.
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redo is designed to update its targets atomically, and only
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if the do script succeeds (ie. returns a zero exit code).
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Thus, you should never write directly to the target file,
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only to $3 or stdout.
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Normally, a .do script will call other .do scripts
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recursively, by running either `redo` (which will always
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build the sub-target) or `redo-ifchange` (which only
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rebuilds the sub-target if its dependencies have changed).
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Running `redo-ifchange` is also the way your .do script
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declares dependencies on other targets; any target that is
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`redo-ifchange`d during your .do script's execution is both
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executed (if needed) and added as a dependency.
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You may have heard that 'recursive make is considered
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harmful' (http://miller.emu.id.au/pmiller/books/rmch/).
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Unlike `make`(1), redo does correct locking, state
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management, and global dependency checking, so none of the
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arguments in that essay apply to redo. In fact, recursive
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redo is really the only kind of redo.
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# RELATED COMMANDS
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When writing a .do script, it will probably need to run
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one or more of the following commands:
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`redo`
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: to build a sub-target unconditionally.
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`redo-ifchange`
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: to build a sub-target only if the sub-target's
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dependencies have changed.
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`redo-ifcreate`
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: to tell redo that the current target must be rebuilt if
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a particular file gets created.
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`redo-always`
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: to tell redo that the current target must always be
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rebuilt, even if someone calls it using `redo-ifchange`.
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(This might happen if the current target has
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dependencies other than the contents of files.)
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`redo-stamp`
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: to tell redo that even though the current target has
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been rebuilt, it may not actually be any different from
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the previous version, so targets that depend on it
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might not need to be rebuilt. Often used in
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conjunction with `redo-always` to reduce the impact of
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always rebuilding a target.
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# CREDITS
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The original concept for `redo` was created by D. J.
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Bernstein and documented on his web site
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(http://cr.yp.to/redo.html). This independent implementation
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was created by Avery Pennarun and you can find its source
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code at http://github.com/apenwarr/redo.
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# SEE ALSO
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`sh`(1), `make`(1),
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`redo-ifchange`(1), `redo-ifcreate`(1), `redo-always`(1),
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`redo-stamp`(1)
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