Is there a way to include the ~ in the output of realpath

Question

realpath is very nice in that it gives you a simple way to get the real path of a file, but I can't figure out a way to satisfy my needs (without doing my own string manipulation, and therefore potentially missing the corner cases that a dedicated utility presumably has found and solved). In a nutshell, I want to include ~ in the path that it returns, so it can be valid across machines.

So if I'm in ~/bin and I type realpath --some-option script.sh I want it to return ~/bin/script.sh instead of bin/script.sh, which is what I get if the option I use is --relative-base=$HOME, and instead of /Users/brandon/bin/script.sh, which is what I get if I use no options.

Is there some way to get what I want from realpath, or is there some other utility that does what I want in a simple way? Or is the only real option to just pipe through sed to get what I want?

(P.S. I'm on OS X, but I've got GNU utilities installed, in case those are needed... I'm not sure if that's where realpath came from or if it's now installed by default on more recent versions of OS X.)

In general, having the `~` is harmful for purposes other than human display -- shells only do tilde expansion in a small set of cases, and `open()` and the like won't honor it at all. — Charles Duffy, Jan 06 '16 at 20:35
It's obviously not difficult to just pipe through sed, but it seems like there *ought* to be something already builtin that I'm overlooking... otherwise its `realpath ../some/path/ | sed -e "s|$HOME|~|"` — iconoclast, Jan 06 '16 at 20:35
@CharlesDuffy: I'll be writing the code that consumes the paths, so I can make sure it handles `~` okay. But your point might be the reason that no one else has seen fit to add this option to `realpath`. — iconoclast, Jan 06 '16 at 20:37
Assuming you're capturing to a shell variable, one can of course do something like `[[ $path = "$HOME"/* ]] && path="~/"${path#"$HOME/"}` with less overhead than starting an external command such as `sed` (and fewer bugs -- no chance of characters in the home directory name being treated as regex content rather than literals). — Charles Duffy, Jan 06 '16 at 20:39

score 2 · Answer 1 · edited May 23 '17 at 11:50

Even the current version of OSX (10.11.3) does not come with a realpath utility, so yours must indeed come from the GNU coreutils Homebrew package.

In fact, you can easily verify that with realpath itself; e.g.:

$ realpath "$(which realpath)"
/usr/local/Cellar/coreutils/8.24/bin/grealpath

Using --relative-base="$HOME" and simply prepending ~/, as in Bujiraso's helpful answer is the simplest solution in your case.

Let me propose an alternative that:

Makes do without realpath, because its presence cannot be assumed on OSX machines.
- A Perl one-liner is used instead (Python would also be an option).
Uses $HOME instead of ~, as basing a path on $HOME is the safer choice (assuming a shell expands the path):
- $HOME is safer, because it allows the entire path string to be double-quoted when it is passed to the shell, without having to worry about individually quoting (escaping) embedded spaces and other shell metacharacters; by contrast, with a ~-prefixed path you'd either have to quote individual characters in the path or selectively leave the ~/ prefix unquoted (~/"path/...").

absPath=$(perl -MCwd -le 'print Cwd::abs_path(shift)' "script.sh")
abstractPath="\$HOME${absPath#"$HOME"}"

The result would be something like literal $HOME/bin/script.sh, which, when interpreted by the shell, would expand to a then-current-user-specific path.

If you define an abstractHomePath() bash function as printed below, you can use:

abstractPath=$(abstractHomePath "script.sh")  # -> '$HOME/bin/script.sh'

abstractHomePath Bash function:

# Given a relative or absolute path, returns an absolute path in which the path
# prefix that is the current user's home directory is replaced with literal
# '$HOME' so as to yield an abstract path that can later be expanded in a 
# different user's context to get the analogous path. 
#
# If the input path resolves to an absolute path that is *not* prefixed with
# the current user's home diretory path, the absolute path is returned as -is.
#
# Note that any symlinks in the path are resolved to their ultimate targets
# first and that the path is normalized.
#
# Examples:
#    abstractHomePath ~ # -> '$HOME'
#    abstractHomePath /Users/jdoe/Downloads # -> '$HOME/Downloads'
#    abstractHomePath /tmp # -> '/private/tmp' -  symlink resolved, but no $HOME prefix
# Prerequisites:
#    Requires Perl v5+
abstractHomePath() {
  local absPath=$(perl -MCwd -le 'print Cwd::abs_path(shift)' "$1")
  if [[ $absPath == "$HOME"* ]]; then
    printf '%s\n' "\$HOME${absPath#"$HOME"}"
  else
    printf '%s\n' "$absPath"
  fi
}

score 1 · Answer 2 · answered Feb 27 '16 at 19:18

realpath itself does not seem to have this functionality, however a simple solution might be to echo the prefix of tilde+slash itself, followed by the relative realpath. That is, you could use a combination of the relative-base and echo, instead of sed. For example:

[user@localhost ~]$ echo "~/$(realpath --relative-base=$HOME bin/myScript)"
~/bin/myScript

Is there a way to include the ~ in the output of realpath

2 Answers2