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resource:sc_lab_info:fedora:makefiles [2016/03/27 11:35] (current)
rim created
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 +====== Makefiles ======
 +Makefiles are command files used by the "​make"​ or "​gmake"​ system to create a software system (or sometimes other object, such as documentation) from sources. ​
  
 +The important thing for //users// to remember is\\
 +== Never Execute a Makefile ==
 +The syntax is fairly different from shell or other scripts; nevertheless,​ it occurs surprisingly often that a shell interpreter is able to '​interpret'​ the first few lines of a makefile. If, as often occurs, the first template happens to be one for uninstalling the package, the results can be disastrous. For example, if the variables $dir, $base and $ext haven'​t been initialised in a way the shell can understand, then
 +  rm $dir/​$base*$ext
 +might well get interpreted as 
 +  rm /*
 +
 +====== ​ ======
 +
 +The important thing for //​developers//​ to remember is\\
 +== Always protect Users from Executing a Makefile ==
 +For the reasons above, I strongly recommend, if you are writing a makefile, to include as early as possible in your file something like:
 +
 +  # Template to protect users against accidentally ​
 +  # executing a makefile - skipped if called by make
 +  # if called as a script,
 +  # it should barf on the unexpected "​ifeq", ​
 +  # but even if it manages to ignore that, 
 +  # it should print and exit
 +  # Note that this protection is needed, because makefiles ​
 +  # can sometimes be valid shell scripts - witness the  ​
 +  # standard XMILL makefile that manages to skip errors
 +  # till it gets to
 +  # clean:
 +  # rm -r -f $(TMP)/* $(TARGETS)
 +  # when executed in most unix shells - 
 +  # which isn't very nice if $(TMP) is undefined...
 +  ifeq (1,0)
 +    echo "THIS IS NOT A SHELL SCRIPT!!!!"​
 +    echo "IT IS A CONFIGURATION FILE FOR THE make SYSTEM"​
 +    echo "DO NOT EXECUTE IT"
 +    exit 1
 +  endif
 +
 +This won't affect the execution of the makefile at all, because 1 will never equal 0 (so the nested part will never even be seen by make)
 +
 +It works as a protection in all unix shells I have tried; it may not work as well in DOS, but I assume it would at least cause an abort.