outputs 'Done updating aliases' to announce its success.
Notice that the second and third lines of the recipe are indented. They must be indented with a tab, not multiple spaces. Why? My theory is that the original creator of make wanted to punish me every time I use cut-and-paste on a system that turns tabs into spaces. However, I don't take it personally.
The update doesn't happen automatically. You have to run make to make it happen: Server1# make aliases.db newaliases Done updating aliases Server1#
That's it! make read its configuration file, figured out that aliases was newer than aliases.db by checking the timestamp of the files, and determined that running newaliases would bring aliases.db up-to-date. If we run it again: Server1# make aliases.db Server1#
There's no output. Why? Because now the timestamps on the files indicate that there is no work to be done: aliases.db is newer than aliases. make is lazy and will calculate the minimum amount of work required to do what you ask. It makes these decisions based on the timestamps of the files.
Here's another Makefile code sample: file1.output: file1.input command1 <file.input >file.output file2.output: file2.input command2 file2.input >$@
In the first example, the command to be run uses stdin and stdout (file redirection using < and >) to read file.input and write file.output. The second example is similar, but the command takes the input filename on the command line and redirects the output to...what? Oh, $@ means 'The file that this recipe is creating,' or, in this case, file2.output. Why isn't it something simple like $me or $this? Who knows! You don't have to use $@, it just makes you look smarter than your coworkers.
make with no command-line parameters runs the first recipe in Makefile. It is traditional to name the first recipe all and have it run all the recipes you would expect as the default. This way, running make makes all the important recipes. It might not be literally all the recipes, but it is all the recipes you want to make by default. It might look like this: all: aliases.db access.db
make with no options then makes sure that aliases.db and access.db are up-to-date. Since there is no command as part of all, no file called all will be created. Thus, make always thinks that all is out-of-date ('Doesn't exist' equals 'Is out of date'). You'll soon see why that is important.
Remember that make is lazy. If access.db is out-of-date but the other file isn't, it just runs the commands to bring access.db up-to-date. In fact, if bringing access.db up-to-date required something else, and that required something else, and so on, make would very intelligently do just the minimum work required.
In addition to all, I usually include a couple of other useful commands: reload: postfix reload stop: postfix stop start: postfix start
Think about what that means. If I run make reload, make is going to notice that there is no file called reload, so it will run postfix reload thinking that the command will create a file called reload. Ah ha! I fooled them, didn't I? The command I listed tells postfix to reload its configuration. That command doesn't create a file called reload at all! Therefore, the next time I run make reload, make will run the command again. In other words, if you want something to always happen, make sure the recipe simply doesn't create the file that make is expecting to create.
With the above code in my Makefile, I can reload, stop, and start postfix by typing make reload, make stop, or make start, respectively. If there are other things that should be stopped (for
