Question

I am doing some basic file manipulations, and would like to store the name the file passed to an executable C program and create a new file that has an extension tacked on the original filename. For example, if this were what I typed on the command line:

a.out < some_file.txt

Where a.out is an executable, is there a way to get the string some_file.txt, so I could open up a new file and call it some_file.text.mod or something else?

argv[0] gets you a.out, and in scripting you could use $1 to access arguments (but not the filenames used in redirection), but neither of those is much use here.

Any ideas?

Answer 1

Sometime (and almost always in practice) /proc/self/fd/0 could be a symbolic link to the file. (But the symlink could be crappy, e.g. for a pipe, and this is Linux specific).

So from inside your a.out you could call the readlink(2) system call on /proc/self/fd/0

But doing that is a bit disgusting. However it works:

% ls -l /proc/self/fd/0 < ~/.zshrc
lr-x------ 1 basile basile 64 Nov  6 19:22 /proc/self/fd/0 -> /home/basile/.zshrc

% date | ls -l /proc/self/fd/0
lr-x------ 1 basile basile 64 Nov  6 19:23 /proc/self/fd/0 -> pipe:[599869]

Again, it is highly Linux specific and not portable to other Posix systems.