Date: Fri, 24 Nov 2006 14:21:47 +0100 (CET) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-standards@FreeBSD.ORG, sa2c@sa2c.net Subject: Re: type command bahaviour of FreeBSD's /bin/sh (Fwd: [issue426] ?hgmerge assumes FileMerge to be exist unconditionally on FreeBSD) Message-ID: <200611241321.kAODLlu6059664@lurza.secnetix.de> In-Reply-To: <7a2b18c80611240418w43776195p340d1ff49ac69786@mail.gmail.com>
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NIIMI Satoshi wrote:
> FreeBSD's /bin/sh produces:
> | % sh -c 'type /nonexistent; echo $?'
> | /nonexistent: No such file or directory
> | 0
Note that the "type" utility is normally not called
with a full path, but with a command name. In that
case it behaves correctly:
$ type asdfg
asdfg: not found
$ echo $?
127
If you have a full path name and need to know whether
it exists, you should rather use the "test" utility
instead of "type". The purpose of "type" is to find
out how a _name_ would be interpreted when given as
a command (i.e. keyword, builtin, alias, shell function
or $PATH expansion).
> Does the current behaviour of /bin/sh's type command conform to the standards?
SUSv3/POSIX2001 is not very clear, unfortunately. It
doesn't exactly explain how the "type" utility should
behave when given a non-existing absolute path. I tend
to believe that it's not a bug in FreeBSD, but rather
a valid interpretation of the standard.
> > Because of the above feature (bug?), testing
> > "/Developer/.../FileMerge" always succeeds and used unconditionally.
> > I made a patch to work around this.
As I said above, it is _wrong_ to use "type" for testing
the existence of a file whose full path is known. Use
"test" (a.k.a. "[") for that purpose:
if [ -f "$FULLPATH" ]; then
# ... found
else
# ... not found
fi
Even if you need to find out whether a name expands to
an external command, it is _not_ sufficient to only check
the return code of "type". You also need to parse the
output in order to check whether it returned a full path
(as opposite to "shell builtin", "alias" or whatever).
In fact it is non-trivial, because the output format of
the "type" builtin is not standardized and varies between
shells. Therefore, if you need to find a command in the
$PATH list, then it's better to do that yourself using
a shell loop, like this:
FULLPATH=""
OLD_IFS="$IFS"
IFS=":"
for DIR in $PATH; do
if [ -x "$DIR/$COMMAND" ]; then
FULLPATH="$DIR/$COMMAND"
break
fi
done
IFS="$OLD_IFS"
if [ -n "$FULLPATH" ]; then
echo "Found: $FULLPATH"
else
echo "$COMMAND not found"
fi
My conclusion is that you should _never_ use "type" in
portable shell scripts.
Best regards
Oliver
--
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd
Any opinions expressed in this message may be personal to the author
and may not necessarily reflect the opinions of secnetix in any way.
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