Rake Jan 14 2019 rake and make A program can consist of many source code files The files may need to be compiled in a certain order This is always true in Rails Some parts of the program may depend on other parts being up to date A UNIX makefile is a file that describes these dependencies UNIX make is a program that reads a makefile determines the correct order in which to update files and updates them Ruby programs are interpreted not compiled but Rails uses metaprogramming to create source files and data files from other files Consequently something like make is still needed rake provides the same functionality as make but is implemented very differently Rakefiles Rakefiles are written in Ruby The following code fragment expresses that a file file 1 depends on files file 2 and file 3 file file 1 file 2 file 3 We can use this code fragment with a block that tells what to do with the dependency file file 1 file 2 file 3 do code to create file 1 from file 2 and file 3 end A rakefile can consist simply of a number of these blocks Like make rake looks at the modification dates of files and only updates them as necessary First example I This example uses C files as examples Suppose we have the files main c greet h and greet c main c is our usual Hello World program but includes greet h which specifies a greet method on greet c Our target the file we want to build is hello o We have the following dependencies file main o main c greet h file greet o greet c file hello main o greet o To create the target we need to execute these commands cc c o main o main c cc c o greet o greet c cc o hello main o greet o First example II Here s the rakefile file main o main c greet h do sh cc c o main o main c end file greet o greet c do sh cc c o greet o greet c end file hello main o greet o do sh cc o hello main o greet o end Running rake The syntax for running a rake command is rake options VAR VALUE targets Unless we use the option f filename rake will read its commands from a file named rakefile Our target the thing we want to make is named hello in this file so assuming the program on the previous slide is on a file named rakefile we run rake by saying rake hello Additional targets file targets check modification dates hence these tasks are only done when needed Non file tasks are always performed We can specify a default task such as hello like this Non file tasks use the task keyword instead of file task default hello Other non file tasks are clean Remove temporary files created during the build process clobber Remove all files generated during the build process The Rake library implements clean and clobber for you but you have to tell it what files to clean or clobber Do this with FileLists clean and clobber use the lists named CLEAN and CLOBBER respectively Example CLEAN FileList greet o You can use wildcards CLOBBER FileList o Dynamically building tasks Example SRC FileList c SRC each do fn obj fn sub o file obj do sh cc c o obj fn end end Notes Remember that Ruby will do substitution in double quoted strings The file list depends on the source files c files because the object files o files may or may not be present The dependencies between source and object files are specified elsewhere Rake can figure this out Automatically building tasks Rather than dynamically building tasks it s usually easier just to generate them automatically For example In C the object o files depend on the source c files so we can say rule o c do t sh cc c o t name t source end Final result require rake clean CLEAN include o CLOBBER include hello task default hello SRC FileList c OBJ SRC ext o rule o c do t sh cc c o t name t source end file hello OBJ do sh cc o hello OBJ end File dependencies go here file main o main c greet h file greet o greet c Credit These slides cover only the most basic use of rake The extended example used in these slides is taken from http docs rubyrake org read book 1 A more comprehensive explanation of rakefiles can be found at http www martinfowler com articles rake html The End
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