I found that the vimdiff utility is just a soft link to vim. both of the two are located under /usr/bin/ in my Suse11 box. and vimdfiff is a soft link to vim. the interesting thing is that, vimdiff file1 file2 is actually the equivalent of vim -d file1 file2, so in that
sense, the -d option is automatically embedded in the soft link, so my question is as simple as
How?
Vim in its main() function uses argv[0] to differentiate its executable name vim or vimdiff, or etc.
Link to vim main.c that performs this check to differentiate rvim, rview, gvim, gview, vimdiff, gvimdiff, ex, exim.
/*
* Check for: [r][e][g][vi|vim|view][diff][ex[im]]
* If the next character is "e" we run in Easy mode.
* If the next character is "g" we run the GUI version.
* If the next characters are "view" we start in readonly mode.
* If the next characters are "diff" or "vimdiff" we start in diff mode.
* If the next characters are "ex" we start in Ex mode. If it's followed
* by "im" use improved Ex mode.
*/