path_overrides 0.2

Install

path_overrides has been tested on recent OS X and Linux systems. It should work on any POSIX system.

To install, simply run:

$ pip install --user path_overrides

or similar. Installing the Python package blessings is recommended to provide colourised output, but is not required.

Use

Run path_overrides. It will display a list of which executables shadow other (different) executables.

Motivation

If I press the ‘tab’ key a couple of times on a recent Linux or OS X shell, I get a prompt looking something like:

Display all 2228 possibilities? (y or n)

There are over 2000 commands all ready and waiting to be run at a single word being entered. And these don’t all live in one place; they live in a (typically small) number of different locations, which are listed in the PATH environment variable. PATH is an ordered sequence of paths which are searched to find an executable which will be run. This works well for the most part, but as with all things where there isn’t a single namespace, collisions happen. There could be a number of items all with the same name living in different paths all in PATH. In normal use this isn’t a problem; PATH is ordered, and each part of it is a unique no-collisions-possible directory. There is never non-determinism about which executable will ‘win’, and the which shell program will report on ‘which’ path has precedence.

However, unless you are in the habit of regularly running which before executing any command - or only ever run commands with absolute pathnames - there can be surprises; if someone places a executable earlier in the PATH than the one you would expect to be run, it will take precendence. path_overrides will report on any command which overrides a different command later in the PATH. Note it’s quite common to have symlinks from (e.g.) /usr/bin to programs in /bin; since they represent ‘the same command’, path_overrides will ignore these.

Example

This is a run of path_overrides on an OS X machine, currently working in a virtualenv. If blessings is installed, the output will be colourised.

ben$ path_overrides
/Users/ben/.virtualenvs/path_overrides/bin/python overrides /usr/bin/python
/Users/ben/.virtualenvs/path_overrides/bin/easy_install overrides /usr/bin/easy_install
/Users/ben/.virtualenvs/path_overrides/bin/python2.7 (python) overrides /usr/bin/python2.7 (../../System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7)
/Users/ben/.virtualenvs/path_overrides/bin/easy_install-2.7 overrides /usr/bin/easy_install-2.7
/Users/ben/.virtualenvs/path_overrides/bin/pip overrides /usr/local/bin/pip
/Library/Frameworks/Python.framework/Versions/3.4/bin/2to3 (2to3-3.4) overrides /usr/bin/2to3
/usr/bin/ndisasm overrides /usr/local/bin/ndisasm (../Cellar/nasm/2.11.02/bin/ndisasm)
/usr/bin/2to3 overrides /usr/local/bin/2to3 (../../../Library/Frameworks/Python.framework/Versions/3.4/bin/2to3)
/usr/bin/nasm overrides /usr/local/bin/nasm (../Cellar/nasm/2.11.02/bin/nasm)
/usr/local/bin/libpng-config (../Cellar/libpng/1.6.10/bin/libpng-config) overrides /opt/X11/bin/libpng-config (libpng15-config)
/usr/local/bin/fc-match (../Cellar/fontconfig/2.11.1/bin/fc-match) overrides /opt/X11/bin/fc-match
/usr/local/bin/fc-list (../Cellar/fontconfig/2.11.1/bin/fc-list) overrides /opt/X11/bin/fc-list
/usr/local/bin/fc-cat (../Cellar/fontconfig/2.11.1/bin/fc-cat) overrides /opt/X11/bin/fc-cat
/usr/local/bin/fc-cache (../Cellar/fontconfig/2.11.1/bin/fc-cache) overrides /opt/X11/bin/fc-cache
/usr/local/bin/fc-scan (../Cellar/fontconfig/2.11.1/bin/fc-scan) overrides /opt/X11/bin/fc-scan
/usr/local/bin/freetype-config (../Cellar/freetype/2.5.3_1/bin/freetype-config) overrides /opt/X11/bin/freetype-config
/usr/local/bin/fc-validate (../Cellar/fontconfig/2.11.1/bin/fc-validate) overrides /opt/X11/bin/fc-validate
/usr/local/bin/fc-query (../Cellar/fontconfig/2.11.1/bin/fc-query) overrides /opt/X11/bin/fc-query
/usr/local/bin/fc-pattern (../Cellar/fontconfig/2.11.1/bin/fc-pattern) overrides /opt/X11/bin/fc-pattern

Options

In most cases path_overrides does not require any options to be provided, but some exist for occasions such as checking the PATH within an alternate root (e.g. when building an alternate chroot filesystem).

In this case, an explicit PATH can be provided as an argument to the –path argument. An alternate to the default PATH separator (e.g. ‘:’ on POSIX systems, ‘;’ on Windows) can also be provided via the –path-sep argument. Finally, a –root-dir path can be specified which all PATH elements will be considered to be local to. Note that the –root-dir value will not be included in the output which path_overrides gives; it is assumed that the calling program / user is aware of this and the more concise information is preferable.

The following example shows the use of all these options:

$ mkdir -p ~/bin ~/sbin
$ touch ~/bin/{x,y} ~/sbin/{x,y}
$ chmod +x ~/bin/{x,y} ~/sbin/{x,y}
$ path_overrides --path-sep=' ' --path='/bin /sbin' --root-dir='~'
/bin/y overrides /sbin/y
/bin/x overrides /sbin/x

Help

Help is obtained with the –help argument; the version of path_overrides is reported with –version:

Usage: path_overrides [-h] [--version] [-p PATH] [--path-sep PATH_SEP]
                      [--root-dir ROOT_DIR]

Display executables in the PATH which override other (different) programs
later in the PATH

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  -p PATH, --path PATH  provide custom PATH value directly rather than from
                        environment
  --path-sep PATH_SEP   path separator; defaults to system default
  --root-dir ROOT_DIR   assumed root of PATH if given

@codedstructure 2014-2015