stefanschmidt/realpath_verbose.md

## realpath_verbose.md

      
    Raw
  

              realpath_verbose.md
            
          
    Gradually resolving symbolic link chains

Let's say one wants to know where pdflatex is located.
$ type pdflatex
pdflatex is /Library/TeX/texbin/pdflatex

We can see that this path is a symbolic link to pdftex.
$ ls -ld /Library/TeX/texbin/pdflatex
lrwxr-xr-x  1 root  wheel  6 Oct  3  2022 /Library/TeX/texbin/pdflatex -> pdftex

Further we can see that the containing folder is also a symbolic link
$ ls -ld /Library/TeX/texbin
lrwxr-xr-x  1 root  wheel  29 Oct  3  2022 /Library/TeX/texbin -> Distributions/Programs/texbin

...which points to another symbolic link
$ ls -ld /Library/TeX/Distributions/Programs/texbin
lrwxr-xr-x  1 root  wheel  39 Jun 19  2014 /Library/TeX/Distributions/Programs/texbin -> ../.DefaultTeX/Contents/Programs/texbin

...which points to yet another symbolic link
$ ls -ld /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin
lrwxr-xr-x  1 root  wheel  9 Oct  3  2022 /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin -> universal

...which points to one more symbolic link which appears to point to a location within /usr/local.
$ ls -ld /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/universal
lrwxr-xr-x  1 root  wheel  64 Oct  3  2022 /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/universal -> ../../../../../../../usr/local/texlive/2022/bin/universal-darwin

The number of relative path segments is quite numerous so manually resolving them would be a tedious and error-prone procedure.
As a workaround for the appearant lack of builtin functionality we'll temporarily switch the working directory to resolve the relative path segments without resolving the complete remaining symbolic link chain.
$ path=/Library/TeX/Distributions/.DefaultTeX/Contents/Programs/universal

$ pushd $path/$(readlink $path) > /dev/null && pwd && popd > /dev/null
/usr/local/texlive/2022/bin/universal-darwin

We now have arrived at the final destination!
$ ls -ld /usr/local/texlive/2022/bin/universal-darwin
drwxr-xr-x  476 root  wheel  15232 Oct  3  2022 /usr/local/texlive/2022/bin/universal-darwin

Summarizing we have the following symbolic link chains:
/Library/TeX/texbin/pdflatex
-> /Library/TeX/texbin/pdftex

/Library/TeX/texbin
-> /Library/TeX/Distributions/Programs/texbin
-> /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin
-> /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/universal
-> /usr/local/texlive/2022/bin/universal-darwin

It may seem obvious, but while realpath and readlink allow to resolve all symbolic link chains of a path, apparently neither of them has an option to do this step-by-step.
$ greadlink -f /Library/TeX/texbin/pdflatex
/usr/local/texlive/2022/bin/universal-darwin/pdftex

$ realpath /Library/TeX/texbin/pdflatex
/usr/local/texlive/2022/bin/universal-darwin/pdftex

This is where realpath_verbose.py comes in, which provides a merged view for symbolic link chains pointing to directories and/or files.
$ ./realpath_verbose.py /Library/TeX/texbin/pdflatex
-> /Library/TeX/texbin/pdftex
-> /Library/TeX/Distributions/Programs/texbin/pdftex
-> /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin/pdftex
-> /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/universal/pdftex
-> /usr/local/texlive/2022/bin/universal-darwin/pdftex

This leaves the question remaining how meaningful such rather lengthy symbolic chains are and assuming one approves the idea if there is something like a maximum chain length.

  
## realpath_verbose.py
#!/usr/bin/env python

from os import sep, readlink
from os.path import islink, join, normpath, dirname, basename
import sys

def resolve_symlinks(path):
    path_list = []
    while islink(path):
        resolved = readlink(path)
        path = normpath(join(dirname(path), resolved))
        path_list.append(path)
    return path_list

def resolve_path(path):
    path_list = []
    base_name = basename(path)
    parts = path.split(sep)
    for i in range(len(parts), 0, -1):
        partial_path = sep.join(parts[:i])
        path_remainder = sep.join(parts[i:])
        if islink(partial_path):
            path_list.extend(resolve_symlinks(partial_path))
            path_list = [path + sep + base_name for path in path_list]
            break
    return path_list

if len(sys.argv) == 2:
    path = normpath(sys.argv[1])
else:
    print('Usage: python realpath_verbose.py <path>')
    sys.exit()

path_list = resolve_symlinks(path)

if path_list:
    path_list.extend(resolve_path(path_list[-1]))

for path in path_list:
    print('-> ' + str(path))
	#!/usr/bin/env python

	from os import sep, readlink
	from os.path import islink, join, normpath, dirname, basename
	import sys

	def resolve_symlinks(path):
	path_list = []
	while islink(path):
	resolved = readlink(path)
	path = normpath(join(dirname(path), resolved))
	path_list.append(path)
	return path_list

	def resolve_path(path):
	path_list = []
	base_name = basename(path)
	parts = path.split(sep)
	for i in range(len(parts), 0, -1):
	partial_path = sep.join(parts[:i])
	path_remainder = sep.join(parts[i:])
	if islink(partial_path):
	path_list.extend(resolve_symlinks(partial_path))
	path_list = [path + sep + base_name for path in path_list]
	break
	return path_list

	if len(sys.argv) == 2:
	path = normpath(sys.argv[1])
	else:
	print('Usage: python realpath_verbose.py <path>')
	sys.exit()

	path_list = resolve_symlinks(path)

	if path_list:
	path_list.extend(resolve_path(path_list[-1]))

	for path in path_list:
	print('-> ' + str(path))