| Well, here is the relevant ChangeLog entry:
|
| Thu Feb 2 11:32:07 1995 David J. MacKenzie <[EMAIL PROTECTED]>
|
| * acgeneral.m4 (AC_CACHE_SAVE): Workaround Ultrix and 4.3BSD sh
| bug in setting the high bit on variable values.
| From Ken Raeburn.
|
| Ken Raeburn is [EMAIL PROTECTED], if you want to ask him about it.
Yep, thanks. I had found the ChangeLog entry, asked him, but had no
reply.
| I can replicate this bug on Ultrix with this shell script:
|
| rm -f foo.cache
| ac_cv_path_M4=/usr/bin/m4
| (set) 2>&1 |
| sed -n "s/^\([a-zA-Z0-9_]*_cv_[a-zA-Z0-9_]*\)=\(.*\)/: \${\1='\2'}/p" \
| >> foo.cache
| /bin/sh -c '
| . foo.cache
| echo $ac_cv_path_M4
| (set) 2>&1 |
| sed -n "s/^\([a-zA-Z0-9_]*_cv_[a-zA-Z0-9_]*\)=\(.*\)/: \${\1='"'"'\2'"'"'}/p" \
| >> foo.cache
| echo $ac_cv_path_M4
| cat -v foo.cache'
|
| On Ultrix, the output is this:
|
| /usr/bin/m4
| /usr/bin/m4
| : ${ac_cv_path_M4='/usr/bin/m4'}
| : ${ac_cv_path_M4='M-/M-uM-sM-rM-/M-bM-iM-nM-/M-mM-4'}
Aaaaaaaah, OK. I thought the ChangeLog meant the 8th bit was not
*preserved*. And I could not find a valid explanation to understand
why it would preserve something to assign twice instead of once :)
| This bug does not happen if I change the use of /bin/sh in the script
| to /bin/sh5, and invoke the script with /bin/sh5. In that case, I see
| this:
|
| /usr/bin/m4
| /usr/bin/m4
| : ${ac_cv_path_M4='/usr/bin/m4'}
| : ${ac_cv_path_M4='/usr/bin/m4'}
OK, thanks!
| Note that the ChangeLog entry indicates that this bug arises on the
| 4.3BSD shell as well. The BSD shells used to use the high bit to
| record information--that is, they were not eight bit clean.
Not being 8 bit clean is something I can understand. Here I wouldn't
call it even 7 bits clean.
| This was
| a problem with csh in particular for years. I'm pretty certain that
| 4.3BSD did not have a second shell like the Ultrix /bin/sh5. On the
| other hand, I don't know whether anybody still runs 4.3BSD.
On AIX the solution is bsh. I don't understand the point of having
several Bourne shells actually.
| That is correct: there are no shells on those machines which support
| functions. In those days machines only had one shell. Ultrix only
| has two shell programs because it is trying to merge BSD and Sysem V;
| /bin/sh is the BSD shell, and /bin/sh5 is the System V shell. Having
| two shells is just a holdover from the BSD/System V split. Presumably
| modern systems drop the two shells as they become POSIX.2 compliant.
This answers the previous question, and I guess it explains the `b' of
`bsh'.
| SVR2 came out in 1984. Eunice is a Unix simulator which runs on VMS.
| A little net spelunking reveals that it was around in 1982.
Hm, pretty comparable, but the difference is probably that there are
few VMS machines today.
| I just checked Horton's Portable C Programming. He says ``There have
What is it? A book?
| been some features added to the Bourne shell since V7 that are not
| portable. These include the : operator used with parameter expansion:
| ${x:-y} and the use of # for comments. Systems derived from V7, such
| as 4BSD, do not support these features. The test or [ commands also
| vary from system to system.''
OK. Thanks a lot Ian, the cache syntax has been a mystery to me for a
long time.
Akim
