Jan Palus dixit:
[ note from IRC, this is on PLD Linux ]
>project -- just made an observation in my Linux distribution of choice
>which has mksh as /bin/sh.
\o/
|
/ \
>1. Looking at the expression in a simplified form:
>
>OUT=$( ((echo foo; echo $? 1>&3) | :) 3>&1 ) && echo "$OUT"
>
>isn't it supposed to echo only 0?
Yes. It does when you do…
OUT=$( ( (echo foo; echo $? 1>&3) | :) 3>&1 ) && echo "$OUT"
>Both mksh R51 and R52 echo foo and 0,
This is a different bug in each. mksh R50 (which I have at
hand right now) parses it like so…
tg@herc:~ $ foo() {
> OUT=$( ((echo foo; echo $? 1>&3) | :) 3>&1 ) && echo "$OUT"
> }
tg@herc:~ $ typeset -f foo
foo() {
OUT=$(( echo foo ; echo $? >&3 | : ) 3>&1 ) && echo "$OUT"
}
… which is a bug in the code that converts $((…)…) from
parsing $((…)) to $(…) and has been fixed in R52. But
mksh R52 has a different bug:
tglase@tglase:~ $ foo() {
> OUT=$( ((echo foo; echo $? 1>&3) | :) 3>&1 ) && echo "$OUT"
> }
tglase@tglase:~ $ typeset -f foo
foo() {
OUT=$({ ( echo foo ; echo $? >&3 | : ) ; } 3>&1 ) && echo "$OUT"
}
Correct parsing would look like this:
tglase@tglase:~ $ bar() {
> OUT=$( ( (echo foo; echo $? 1>&3) | :) 3>&1 ) && echo "$OUT"
> }
tglase@tglase:~ $ typeset -f bar
bar() {
OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
}
Now we have a timing issue though:
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
0
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
0
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
0
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
0
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | : ) 3>&1 ) && echo "$OUT"
0
The problem here is that : returns immediately, so the 3>&1 and
the end of the command substitution may not catch the $? echo’d
any more. The following code is more reliable:
tglase@tglase:~ $ OUT=$(( ( echo foo ; echo $? >&3 ) | sleep 1 ) 3>&1 ) && echo
"$OUT"
0
>2. In original command large_git produces lots of output to stdout,
>which as described above lands in $OUT both in R51 and R52, but here's
>the awkward difference between the two:
>
>OUT="diff --git"
>test "$OUT" -eq 141 && echo equals || echo not equals
Oh no, you don’t compare strings numerically please.
But this is also a bug that has been fixed in R52.
>Looks like R51 passed git tests only by accident.
Nah, the real cause for the problems here is that the
git tests are broken (replace the “:” with a “sleep 1”
to fix it), plus a parse problem in mksh (which I’ll
fix in R52b now that I know about it).
bye,
//mirabilos
--
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