Getopt is the standard way in c and c++ to parse complex command lines on unix. This tutorial discusses how to use getopt, and provides some simple sample code for your enjoyment. Before you can use getopt, you'll need to include the right header. This isn't very hard. To quote the getopt man page, the required details are: code2dbgetopt-man-simple As we can see from this, we'll need to include the unistd.h header before things will compile. Let's imagine that our program is going to have two command line options. The first will be the name of an input file (otherwise we might read from stdin or something else like that), and the other is an output file (or we'll use stdout). Additionally, there is an extra command line option -g, which turns gronk mode on. Valid command lines might look like (these aren't all the possible combinations): fooapp fooapp -i infile fooapp -i infile -o outfile fooapp -g The way that we tell getopt about these three possible command line options is with the options string. Options which have an arguement are represented in the options string by the letter is that the option, followed by a colon. For example: i:o: Options without an arguement are the same, except that they lack the colon. In our example: g You can mark an optional arguement with two colons. There aren't any of these in my example, but if there was one, then it might look like: m:: Therefore, our complete options string for this example is going to look something like: i:o:g Now that we have an options string, there isn't really all that much more to do. code2dbexample.c You'll note here that there is an extra command line option which we got for free, the ? command line option. This is used to display the usage message you see with many unix applications. We should prove that this works for the sample command line arguements above. [root@localhost howto-getopt]# fooapp Command line parsed to: input = (null), output = (null), gronk = 0 [root@localhost howto-getopt]# fooapp -i infile Command line parsed to: input = infile, output = (null), gronk = 0 [root@localhost howto-getopt]# fooapp -i infile -o outfile Command line parsed to: input = infile, output = outfile, gronk = 0 [root@localhost howto-getopt]# fooapp -g Command line parsed to: input = (null), output = (null), gronk = 1 [root@localhost howto-getopt]# When getopt has returned -1, then it has finished finding arguements. At this point optind will be the index into argv of the first element on the command line which isn't an arguement. getopt will have magically moved all the non-arguements to the end of the command line. You might have noticed that many unix applications now support long command line arguements, such as --with-gronk. To do this, you use a slightly different invokation of getopt. The first thing we need to discuss is how the longer arguements are specified. struct option { const char *name; int has_arg; int *flag; int val; };