How to determine which executable on the path will be run

pathUtilitieswhich

I run which and get the following,

brendan$ which python
  /opt/local/bin/python
brendan$ which -a python
  /opt/local/bin/python
  /usr/bin/python
brendan$ ls -l /opt/local/bin/python
  lrwxr-xr-x  1 root  admin  24 22 Jul 00:45 /opt/local/bin/python -> /opt/local/bin/python2.4
brendan$ python
  Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) 
  ...
  (this is the python version in /usr/local/bin)

My point is, which does not tell me the primary executable, i.e. the one that will be executed in preference. How do I find this out?

I am running OSX 10.6 on a Macbook although the question is general to UNIX-likes.

Update: I have been removing lots of redundant versions of Python on my system (I had at least half a dozen) and removing various crufty PATH declarations in a bunch of initialisation files. In the process, somehow, a fresh shell now shows the expected output (i.e. which shows /opt/local/bin/python and that is what is executed). In any case, thanks for the help!

Best Answer

The one that gets output when you run which without -a is the one which will get executed. (and the second one with -a is preferred over the third one).

This doesn't take into account the shell's builtins, aliases, and functions which will run (from within the shell) before any other executable.

Therefore, it's better to use type instead.

Related Solutions

Centos – Missing ‘which’ executable on CentOS

Solved with:

rpm -e --justdb --nodeps which
sudo yum install which

Still not sure what could have caused this problem though...

How to use which(1) with the system’s default $PATH

command -pv uses a "default value for PATH".

$ which ruby
/home/mikel/.rvm/rubies/ruby-1.9.3-p484/bin/ruby

$ command -pv ruby
/usr/bin/ruby

Unfortunately that doesn't work in zsh, so based on Stephane's comment, we could use getconf PATH:

$ PATH=$(getconf PATH) which ruby

or use command -v in place of which, as recommended in Why not use "which"? What to use then?

$ PATH=$(getconf PATH) command -v ruby

The downside with these approaches is that if the system administrator installed a system-wide version into say /usr/local/bin or /opt/local/bin, and all users had that in PATH (e.g. via /etc/profile or /etc/environment or similar), the above probably wouldn't find it.

In your specific case, I'd suggest trying something specific to Ruby. Here's some ideas that might work:

Filter out versions in the user's home directory (and relative paths):

(
    IFS=:
    set -f
    for dir in $PATH; do
        case $dir/ in
            "$HOME/"*) ;;
            /*/)
                if [ -f "$dir/ruby" ] && [ -x "$dir/ruby" ]; then
                    printf '%s\n' "$dir/ruby"
                    break
                fi;;
        esac
    done
)

Filter out versions in the rvm directory

(
    IFS=:
    set -f
    for dir in $PATH; do
        case $dir/ in
            "$rvmpath/"*) ;;
            /*/)
                if [ -f "$dir/ruby" ] && [ -x "$dir/ruby" ]; then
                    printf '%s\n' "$dir/ruby"
                    break
                fi;;
        esac
    done
)

Filter out writeable rubies (last resort, assumes not running as root)

(
    IFS=:
    set -f
    for dir in $PATH; do
        case $dir/ in
            /*/)
                ruby=$dir/ruby
                if [ -f "$ruby" ] && [ -x "$ruby" ] && [ ! -w "$ruby" ]; then
                    printf '%s\n' "$ruby"
                    break
                fi;;
        esac
    done
)

Ask rvm, chruby, etc.

(
    rvm system
    chruby system
    command -v ruby
)

The last way makes rvm select the default Ruby, but we do it in a subshell, so that the user's preferred Ruby is restored afterwards. (chruby part untested.)

Best Answer

Related Solutions

Centos – Missing ‘which’ executable on CentOS

How to use which(1) with the system’s default $PATH

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