Preben Randhol <randhol@pvv.org> [2002-09-21 10:55:48 +0200]:
> Bob Proulx <bob@proulx.com> wrote on 19/09/2002 (18:07) :
> > quote format just to be explicit. And it makes cut-n-paste easier.
> >
> > which mozilla
> >
> > But instead of that old csh script 'which' I prefer newer commands
> > such as 'command' or 'type'. (Yes I see that on debian which is
> > now a bash script instead of a csh script. But this is not true
> > everywhere.)
> >
> > type mozilla
> >
> > command -v mozilla
>
> Isn't it kind of stupid to suggest a bash only solution? Especially if
> you want to use this in a script like:
>
> #!/bin/sh
> BROWSER=`which mozilla`
It pains me that you used that harsh language to describe my comment.
I never said anything about bash only syntax. Anyone that said so was
just caught up in the excitement of the moment! :-) Those are /bin/sh
syntax, which I prefer better than anything that depends upon
/bin/csh. I don't know why you thought that was bash only. [*]
Those commands are defined by SUSv2. I am pleased that I can refer
you to these pages for your edification. (And perhaps mine too in the
case that I made a mistake here. I am only too well aware that the
sword can cut both ways.)
http://www.unix-systems.org/single_unix_specification_v2/xcu/type.html
http://www.unix-systems.org/single_unix_specification_v2/xcu/command.html
Repeat after me, "Standard is better than better." And then say,
"Every programmer should strive to write portable code." But to do
that one must learn about systems other than their home system. It is
a challenge and very hard to accomplish fully. I have devoted many
years to the task and know that I will never fully achieve the goal.
The 'which' command does not have any standards behind it. Different
systems implement it differently. As has been pointed out by others
in this thread it is very troublesome to use portably across different
operating systems. For example, on most operating systems it is
implemented as a #!/bin/csh script which will read a user's individual
~/.cshrc file and be affected by the contents there!
On the original BSD systems the which command was a #!/bin/csh script.
It still is on most systems. I found it strange that on Debian it was
a bash script! It trades one set of problems for another different
set of problems. The man page on systems where this is a csh script
contains these warnings reproduced here.
WARNINGS
which reports .cshrc aliases even when not invoked from csh.
which cannot find csh built-in commands (e.g. jobs).
which's information may be incorrect because it is unaware of any path
or alias changes that have occurred in the current shell session.
The POSIX shell is based upon the AT&T ksh. Both the posix shell and
ksh define 'whence' instead of other things. As a precompiled builtin
to those shells, which may be changed at compile time, aliases for
type are provided where type='whence -v'. Normal ksh users have
always learned to use 'whence' as the command to find things. Normal
csh users have always learned 'which' as the command to find things.
The old Bourne /bin/sh did neither. It really is getting hard to find
a standard way of finding executable files!
The 'whereis' command is yet different still. It does not look on
_your_ path. It looks in the system provided path. This would
include places like /usr/src, /usr/man, /usr/lib and other such places
tht might not be on your path but where the 'whereis' command might be
able to find the file you were looking for. It finds source code, man
pages, and not just binaries. (I am pretty sure that at one time it
would load up the path the system loaded up in /etc/rc but my memory
is faded and I may be confusing it with another command.)
I am almost ready to meantion the BSD fast find command since
mentioning 'whereis' transitions to finding general files. We now
know the BSD fast find as the 'locate' command. But I seriously
take this thread off topic if I do that. :-)
Bob
Footnote [*]: 'type' works in all posix sh, ash, bash, zsh, I just
checked. 'command' works everywhere but zsh but zsh does not claim to
be a POSIX complaint shell, not suitable for /bin/sh so that is okay.
It even works in csh, on other systems like hpux, I just checked.
(HPUX probably improved the command for standards conformance. A
standard csh, ha!) It did not work on csh on Debian, however, did not
expect it to work and mentioned that specifically. I am sure that
those would _not_ work on older, true Bourne shell /bin/sh systems, I
said it was a newer syntax. Many people who used the older systems
will have learned to avoid this on Bourne shells because of that.
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