If you don't have readlink or realpath utilities than you can use following function which works in bash and zsh (not sure about the rest).
abspath () { case "$1" in /*)printf "%s\n""$1";; *)printf "%s\n""$PWD/$1";; esac; }This also works for nonexistent files (as does the python function os.path.abspath).
Unfortunately abspath ./../somefile doesn't get rid of the dots.