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diff --git a/doc/user/actions.in b/doc/user/actions.in new file mode 100644 index 0000000..1ea5c49 --- /dev/null +++ b/doc/user/actions.in @@ -0,0 +1,404 @@ +<!-- + + Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 The SCons Foundation + + Permission is hereby granted, free of charge, to any person obtaining + a copy of this software and associated documentation files (the + "Software"), to deal in the Software without restriction, including + without limitation the rights to use, copy, modify, merge, publish, + distribute, sublicense, and/or sell copies of the Software, and to + permit persons to whom the Software is furnished to do so, subject to + the following conditions: + + The above copyright notice and this permission notice shall be included + in all copies or substantial portions of the Software. + + THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY + KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE + WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE + LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION + OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION + WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. + +--> + +<!-- + +=head1 Build actions + +Cons supports several types of B<build actions> that can be performed +to construct one or more target files. Usually, a build action is +a construction command, that is, a command-line string that invokes +an external command. Cons can also execute Perl code embedded in a +command-line string, and even supports an experimental ability to build +a target file by executing a Perl code reference directly. + +A build action is usually specified as the value of a construction +variable: + + $env = new cons( + CCCOM => '%CC %CFLAGS %_IFLAGS -c %< -o %>', + LINKCOM => '[perl] &link_executable("%>", "%<")', + ARCOM => sub { my($env, $target, @sources) = @_; + # code to create an archive + } + ); + +A build action may be associated directly with one or more target files +via the C<Command> method; see below. + +=head2 Construction commands + +A construction command goes through expansion of construction variables +and C<%-> pseudo-variables, as described above, to create the actual +command line that Cons will execute to generate the target file or +files. + +After substitution occurs, strings of white space are converted into +single blanks, and leading and trailing white space is eliminated. It +is therefore currently not possible to introduce variable length white +space in strings passed into a command. + +If a multi-line command string is provided, the commands are executed +sequentially. If any of the commands fails, then none of the rest are +executed, and the target is not marked as updated, i.e. a new signature is +not stored for the target. + +Normally, if all the commands succeed, and return a zero status (or whatever +platform-specific indication of success is required), then a new signature +is stored for the target. If a command erroneously reports success even +after a failure, then Cons will assume that the target file created by that +command is accurate and up-to-date. + +The first word of each command string, after expansion, is assumed to be an +executable command looked up on the C<PATH> environment variable (which is, +in turn, specified by the C<ENV> construction variable). If this command is +found on the path, then the target will depend upon it: the command will +therefore be automatically built, as necessary. It's possible to write +multi-part commands to some shells, separated by semi-colons. Only the first +command word will be depended upon, however, so if you write your command +strings this way, you must either explicitly set up a dependency (with the +C<Depends> method), or be sure that the command you are using is a system +command which is expected to be available. If it isn't available, you will, +of course, get an error. + +Cons normally prints a command before executing it. This behavior is +suppressed if the first character of the command is C<@>. Note that +you may need to separate the C<@> from the command name or escape it to +prevent C<@cmd> from looking like an array to Perl quote operators that +perform interpolation: + + # The first command line is incorrect, + # because "@cp" looks like an array + # to the Perl qq// function. + # Use the second form instead. + Command $env 'foo', 'foo.in', qq( + @cp %< tempfile + @ cp tempfile %> + ); + +If there are shell meta characters anywhere in the expanded command line, +such as C<E<lt>>, C<E<gt>>, quotes, or semi-colon, then the command +will actually be executed by invoking a shell. This means that a command +such as: + + cd foo + +alone will typically fail, since there is no command C<cd> on the path. But +the command string: + + cd $<:d; tar cf $>:f $<:f + +when expanded will still contain the shell meta character semi-colon, and a +shell will be invoked to interpret the command. Since C<cd> is interpreted +by this sub-shell, the command will execute as expected. + +=head2 Perl expressions + +If any command (even one within a multi-line command) begins with +C<[perl]>, the remainder of that command line will be evaluated by the +running Perl instead of being forked by the shell. If an error occurs +in parsing the Perl code, or if the Perl expression returns 0 or undef, +the command will be considered to have failed. For example, here is a +simple command which creates a file C<foo> directly from Perl: + + $env = new cons(); + Command $env 'foo', + qq([perl] open(FOO,'>foo');print FOO "hi\\n"; close(FOO); 1); + +Note that when the command is executed, you are in the same package as +when the F<Construct> or F<Conscript> file was read, so you can call +Perl functions you've defined in the same F<Construct> or F<Conscript> +file in which the C<Command> appears: + + $env = new cons(); + sub create_file { + my $file = shift; + open(FILE, ">$file"); + print FILE "hi\n"; + close(FILE); + return 1; + } + Command $env 'foo', "[perl] &create_file('%>')"; + +The Perl string will be used to generate the signature for the derived +file, so if you change the string, the file will be rebuilt. The contents +of any subroutines you call, however, are not part of the signature, +so if you modify a called subroutine such as C<create_file> above, +the target will I<not> be rebuilt. Caveat user. + +=head2 Perl code references [EXPERIMENTAL] + +Cons supports the ability to create a derived file by directly executing +a Perl code reference. This feature is considered EXPERIMENTAL and +subject to change in the future. + +A code reference may either be a named subroutine referenced by the +usual C<\&> syntax: + + sub build_output { + my($env, $target, @sources) = @_; + print "build_output building $target\n"; + open(OUT, ">$target"); + foreach $src (@sources) { + if (! open(IN, "<$src")) { + print STDERR "cannot open '$src': $!\n"; + return undef; + } + print OUT, <IN>; + } + close(OUT); + return 1; + } + Command $env 'output', \&build_output; + +or the code reference may be an anonymous subroutine: + + Command $env 'output', sub { + my($env, $target, @sources) = @_; + print "building $target\n"; + open(FILE, ">$target"); + print FILE "hello\n"; + close(FILE); + return 1; + }; + +To build the target file, the referenced subroutine is passed, in order: +the construction environment used to generate the target; the path +name of the target itself; and the path names of all the source files +necessary to build the target file. + +The code reference is expected to generate the target file, of course, +but may manipulate the source and target files in any way it chooses. +The code reference must return a false value (C<undef> or C<0>) if +the build of the file failed. Any true value indicates a successful +build of the target. + +Building target files using code references is considered EXPERIMENTAL +due to the following current limitations: + +=over 4 + +Cons does I<not> print anything to indicate the code reference is being +called to build the file. The only way to give the user any indication +is to have the code reference explicitly print some sort of "building" +message, as in the above examples. + +Cons does not generate any signatures for code references, so if the +code in the reference changes, the target will I<not> be rebuilt. + +Cons has no public method to allow a code reference to extract +construction variables. This would be good to allow generalization of +code references based on the current construction environment, but would +also complicate the problem of generating meaningful signatures for code +references. + +=back + +Support for building targets via code references has been released in +this version to encourage experimentation and the seeking of possible +solutions to the above limitations. + +--> + + <para> + + &SCons; supports several types of &build_actions; + that can be performed to build one or more target files. + Usually, a &build_action; is a command-line string + that invokes an external command. + A build action can also be an external command + specified as a list of arguments, + or even a Python function. + + </para> + + <para> + + Build action objects are created by the &Action; function. + This function is, in fact, what &SCons; uses + to interpret the &action; + keyword argument when you call the &Builder; function. + So the following line that creates a simple Builder: + + </para> + + <sconstruct> + b = Builder(action = 'build < $SOURCE > $TARGET') + </sconstruct> + + <para> + + Is equivalent to: + + </para> + + <sconstruct> + b = Builder(action = Action('build < $SOURCE > $TARGET')) + </sconstruct> + + <para> + + The advantage of using the &Action; function directly + is that it can take a number of additional options + to modify the action's behavior in many useful ways. + + </para> + + <section> + <title>Command Strings as Actions</title> + + <section> + <title>Suppressing Command-Line Printing</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>Ignoring Exit Status</title> + + <para> + + XXX + + </para> + + </section> + + </section> + + <section> + <title>Argument Lists as Actions</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>Python Functions as Actions</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>Modifying How an Action is Printed</title> + + <section> + <title>XXX: the &strfunction; keyword argument</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>XXX: the &cmdstr; keyword argument</title> + + <para> + + XXX + + </para> + + </section> + + </section> + + <section> + <title>Making an Action Depend on Variable Contents: the &varlist; keyword argument</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>chdir=1</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>Batch Building of Multiple Targets from Separate Sources: the &batch_key; keyword argument</title> + + <para> + + XXX + + </para> + + </section> + + <section> + <title>Manipulating the Exit Status of an Action: the &exitstatfunc; keyword argument</title> + + <para> + + XXX + + </para> + + </section> + + <!-- + + ??? + + <section> + <title>presub=</title> + + <para> + + XXX + + </para> + + </section> + + --> |