Shell – Why does the “which” command give duplicate results

I would guess that you have /home/sawa/foo/bar/ on your path - i.e. a path with a trailing slash.

which is iterating over each element of $PATH and appending /argv[1] and checking for the existence of that file. That causes a double-slash - one from the $PATH part, and one from /argv[1].

A double-slash is no problem. It is collapsed to a single slash by the kernel. Only at the beginning of a path may a double-slash have special meaning, and not always then.

As for test not working, ensure you are not using the shell built-in when calling test. You usually do this by using a full path, but with bash you can also use enable -n test to disable the built-in test command.

The three possibilities that come to mind for me:

• An alias exists for emacs (which you've checked)
• A function exists for emacs
• The new emacs binary is not in your shell's PATH hashtable.

You can check if you have a function emacs:

bash-3.2$ declare -F | fgrep emacs
declare -f emacs

And remove it:

unset -f emacs

Your shell also has a PATH hashtable which contains a reference to each binary in your PATH. If you add a new binary with the same name as an existing one elsewhere in your PATH, the shell needs to be informed by updating the hashtable:

hash -r

Additional explanation:

which doesn't know about functions, as it is not a bash builtin:

bash-3.2$ emacs() { echo 'no emacs for you'; }
bash-3.2$ emacs
no emacs for you
bash-3.2$ which emacs
/usr/bin/emacs
bash-3.2$ `which emacs` --version | head -1
GNU Emacs 22.1.1

New binary hashtable behaviour is demonstrated by this script.

bash-3.2$ PATH=$HOME/bin:$PATH
bash-3.2$ cd $HOME/bin

bash-3.2$ cat nofile
cat: nofile: No such file or directory
bash-3.2$ echo echo hi > cat
bash-3.2$ chmod +x cat
bash-3.2$ cat nofile
cat: nofile: No such file or directory

bash-3.2$ hash -r
bash-3.2$ cat nofile
hi
bash-3.2$ rm cat
bash-3.2$ cat nofile
bash: /Users/mrb/bin/cat: No such file or directory

bash-3.2$ hash -r
bash-3.2$ cat nofile
cat: nofile: No such file or directory

Although I didn't call it, which cat would always return the first cat in my PATH, because it doesn't use the shell's hashtable.