Double Colon in $PATH

Double Colon in $PATH

[Julius Plenz]

Hi!

I recently discovered (rather by accident, though) that a double-colon
in the PATH variable is treated by Zsh (Ash and Bash, too) as if there was
".", the current directory, in the PATH variable.

Example:

prompt> echo $PATH && pwd
::
/bin
prompt> ls
[directory listing of /bin]

Now this is really confusing me. I've already asked several people,
and neither one of them could tell my why Zsh (and other shells) do
this. I'd appreciate it very much if any of you guys could give me a
hint or explain this behaviour to me.

Thank you!

Julius

Re: Double Colon in $PATH

[Erik Trulsson]

On Sun, May 28, 2006 at 05:32:04PM +0200, Julius Plenz wrote:
> Hi!
> 
> I recently discovered (rather by accident, though) that a double-colon
> in the PATH variable is treated by Zsh (Ash and Bash, too) as if there was
> ".", the current directory, in the PATH variable.
> 
> Example:
> 
> prompt> echo $PATH && pwd
> ::
> /bin
> prompt> ls
> [directory listing of /bin]
> 
> Now this is really confusing me. I've already asked several people,
> and neither one of them could tell my why Zsh (and other shells) do
> this. I'd appreciate it very much if any of you guys could give me a
> hint or explain this behaviour to me.

Spending a few minutes reading man-pages reveals the following:


The man-page for bash(1) says:

 [...]
       PATH   The  search  path for commands.  It is a colon-separated list of
	      directories in which the shell looks for commands  (see  COMMAND
	      EXECUTION  below).   A  zero-length (null) directory name in the
	      value of PATH indicates the current directory.  A null directory
	      name  may  appear  as  two  adjacent colons, or as an initial or
	      trailing colon.  The default path is  system-dependent,  and  is
	      set  by  the administrator who installs bash.  A common value is
	      `/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
 [...]

The sh(1) manpage (on FreeBSD) says:

 [...]
     2.   The shell searches each entry in PATH in turn for the command. The
	  value of the PATH variable should be a series of entries separated
	  by colons.  Each entry consists of a directory name.  The current
	  directory may be indicated implicitly by an empty directory name, or
	  explicitly by a single period.
 [...]


I assume that zsh treats empty directory names in $PATH in the same
way even though I could not find it in the manpages.


-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se

Re: Double Colon in $PATH

[Bart Schaefer]

On May 28,  5:56pm, Erik Trulsson wrote:
}
} I assume that zsh treats empty directory names in $PATH in the same
} way even though I could not find it in the manpages.

The zsh manual started out pretty much describing only the things that
zsh does differently, rather than describing everything it does whether
or not other shells are the same.  It's gradually been improving, but
only as missing bits get noticed.