How to get input file name from Unix terminal in C?
$./sort 1 < test.txt

$ echo "This is the end" | ./sort 1

echo $(readlink /proc/self/fd/0 < /dev/null)

/dev/null

sort << _EOF
3
1
2
_EOF

$ /usr/bin/sleep 3600 < /tmp/foo &
[1] 8430
$ pfiles 8430
8430: /usr/bin/sleep 3600
  Current rlimit: 65536 file descriptors
   0: S_IFREG mode:0600 dev:299,2 ino:36867886 uid:12345 gid:67890 size=123
      O_RDONLY|O_LARGEFILE
      /tmp/foo
   1: S_IFCHR mode:0600 dev:295,0 ino:12569206 uid:12345 gid:67890 rdev:24,2
...