Converting relative path to absolute path without symbolic link

You can use the readlink utility, with the -f option:

-f, --canonicalize

      canonicalize  by  following  every symlink in every component of
      the given name recursively; all  but  the  last  component  must
      exist

Some distributions, for example those that use GNU coreutils and FreeBSD, also come with a realpath(1) utility that basically just calls realpath(3) and does pretty much the same thing.

Portably, the PWD variable is set by the shell to one absolute location of the current directory. Any component of that path may be a symbolic link.

case $f in
  /*) absolute=$f;;
  *) absolute=$PWD/$f;;
esac

If you want to eliminate . and .. as well, change to the directory containing the file and obtain $PWD there:

if [ -d "$f" ]; then f=$f/.; fi
absolute=$(cd "$(dirname -- "$f")"; printf %s. "$PWD")
absolute=${absolute%?}
absolute=$absolute/${f##*/}

There's no portable way to follow symbolic links. If you have a path to a directory, then on most unices $(cd -- "$dir" && pwd -P 2>/dev/null || pwd) provides a path that doesn't use symbolic links, because shells that track symbolic links tend to implement pwd -P (“P” for “physical”).

Some unices provide a utility to print the “physical” path to a file.

• Reasonably recent Linux systems (with GNU coreutils or BusyBox) have readlink -f, as do FreeBSD ≥8.3, NetBSD ≥4.0, and OpenBSD as far back as 2.2.
• FreeBSD ≥4.3 has realpath (it's also present on some Linux systems, and it's in BusyBox).

• If Perl is available, you can use the Cwd module.

  perl -MCwd -e 'print Cwd::realpath($ARGV[0])' path/to/file
  

Is pwd fit for your needs? It gives the absolute path of current directory. Or maybe what you want is realpath().