| > From: Akim Demaille <[EMAIL PROTECTED]>
| > Date: 27 Feb 2002 10:05:42 +0100
|
| > What we want, is to find a reliable `echo', or any means that would
| > help us remove the thousands of heredocs we have.
|
| > elif test "X`($echo '\t') 2>/dev/null`" = 'X\t'; then
| > # Yippee, $echo works!
|
| Unfortunately this approach won't work in the long run.
| POSIX 1003.2-1992 allows echo '\t' to output backslash-t, but
| POSIX 1003.1-2001 requires that it must output a tab character.
| Eventually shells will head in that direction, albeit reluctantly.
Good to know, thanks!
| Here's an idea. How about if we use expr instead of cat? That is
| allowed by the GNU coding standards, and it handles backslash
| correctly. That is, instead of doing this:
|
| cat <<__ACEOF
| some very
| long string
| with funny characters "'\\
| and with $SHELL expansions in it
| __ACEOF
|
| we do this:
|
| expr "Xsome very
| long string
| with funny characters \"'\\
| and with $SHELL expansions in it" : 'X\(.*\)'
|
| If __ACEOF is quoted, the expr version should use ' instead of ",
| and should quote ' rather than " of course.
|
| The problems I see with this approach are:
|
| * expr may be limited in the length of the string that it can handle.
| But we already have this problem with some extent with __ACEOF;
| and we already use expr in similar ways so there is some precedent.
I find this risky, but why not.
| * " is tricky, e.g.
|
| cat <<__ACEOF
| ${foo+"abc"}
| __ACEOF
|
| will be mishandled if we blindly escape all "s in the expr version.
| But that is a problem no matter what program we substitute for
| __ACEOF.
Arg :(
| * expr exits with nonzero status if the string is empty. But we're
| already ignoring the exit status of cat, so I don't see this as a
| real problem.
Actually, all this should be done after an initial step, which is
equipping configure with means to provide replacement functions. I'm
think about something like
./configure --replacement-function=ln -s from to
./configure --replacement-function=echo "Hello world"
and so forth.
This mean equipping M4sh which such a feature. Using diversions,
that's very easy to do. But my problem is that I would like to be
sure of the order we want to follow between the different tests.
Basically, we have several blocks to order:
- sanitizing the shell (``emulate sh'' etc.).
- re-execution (based on LINENO tests currently)
- analysis of various tool limitations (e.g., as_expr=expr or
as_expr=false).
where do we want to add:
- command replacement
Paul, I'm especially interested in your opinion. Currently, I'd
suggest that you toy with autom4te to see how M4sh works. For
instance:
/tmp % cat script.as nostromo 10:40
AS_INIT
AS_SHELL_SANITIZE
echo `AS_DIRNAME(//1/2)`
/tmp % autom4te -l m4sh script.as -o script nostromo 10:40
/tmp % ./script nostromo 10:40
//1
then, where would you place the handling of --replacement-function in
script?
Thanks!
