Automating Tasks with Aap
Listing 4. Rule for Putting a Timestamp in a Generated HTML File
:rule %.html : header.part %_title.part middle.part %.part footer.part :print Generating $-target :cat $source | :eval string.replace(stdin, '@TIMESTAMP@', _no.DATESTR) >! $target
The first time the new rule is used, all HTML files are updated. That is because Aap remembers a signature for the commands. Thus, you don't need to worry about forcefully generating the files after changing the commands in the recipe.
When making small changes to a Web page, it is a waste of bandwidth to upload the whole file each time. A good way to upload efficiently is to use rsync. It uploads only those parts of a file that have been changed. Aap uses rsync when it finds rsync:// in the publish attribute. By default, rsync is used over an SSH connection. You can change this by setting the $RSYNC variable.
rsync is not a standard command. If it does not exist on the system, you encounter a nice feature of Aap—you are offered the choice to install rsync:
% aap Aap: Uploading ['index.html'] to rsync://my.server.net/html/index.html Cannot find package "rsync"! 1. Let Aap attempt installing the package 2. Retry (install it yourself first) q. Quit Choice:
Aap has a mechanism to install a package when it is needed by downloading a recipe from the Aap Web site that specifies how the package is to be installed. The downloading features of Aap come in handy here. How the package is installed depends on your system; not all systems are supported yet. After rsync has been installed, Aap starts uploading the files.
Aap includes support for building a program from C and C++ code. Here is the one-line recipe that builds the program called myprog from four C source files:
:program myprog : main.c common.c various.c args.c
Despite the simplicity of the recipe, Aap takes care of several issues:
Dependencies are figured out automatically. You don't need to specify the included header files or do a make depend.
This recipe works on most systems without modification. Aap finds a compiler and linker to use and figures out the arguments they need.
The object files are stored in a separate build directory for each system. You can build several versions without cleaning up.
Aap creates a log file, AAPDIR/log, that contains details about what happened. If your build fails and the output scrolls off the screen, you don't need to repeat the build command with the output redirected.
A few default targets are added automatically: aap install installs the program, and aap clean deletes generated files.
It would be possible to do the same work with make, with the help of a few extra tools. But the Makefile would be much longer and not portable; it also would require more effort to maintain.
Now let's build a program in two variants, a release and a debug version. Aap includes support for variants. All you need to do is specify what variants you want to build and what is different between them. Listing 5 shows the recipe.
Listing 5. Building Release and Debug Variants
:variant Build release OPTIMIZE = 4 Target = myprog debug DEBUG = yes Target = myprogd :program $Target : main.c common.c various.c args.c
The first line of the :variant command specifies the variable name used to select the variant to be built. You can set this variable on the command line; aap Build=debug builds the debug version. Without an argument, the release variant is built, because it is mentioned first.
The amount of indentation identifies the other parts of the :variant command. The possible values have less indentation; the commands used for each value have a bit more. You are forced to align the parts, which makes them easier to read.
The release variant sets the OPTIMIZE variable. This is a number in the range of zero to nine that indicates the amount of optimizing to be done. It automatically is turned into the right argument for the compiler being used. The debug variant sets DEBUG to yes. The default value is no. The Target variable holds the name of the resulting program. The two variants use a different name, so both programs can exist.
A nice advantage of using variants this way is that object files for each variant are stored automatically in a separate build directory. When switching between the two variants you should notice that Aap does not rebuild all the files.
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