Re: Bug in expr***urgent

[Eric Blake]

According to salih k on 1/16/2010 7:32 AM:
> Piece of Script
> --------------------------
> 
>      /isnum=`awk -F$delim '$1=="BH"{print $5}' $fil`/
>     /

That's still not exactly what you ran (you marked it up afterwards), but
it is close enough, I suppose.

>             int_num=`echo -e $isnum | cut -f1 -d'.'`

echo -e is not portable.  And if all you are trying to do is grab
everything before the first '.', you can do that without even forking:

int_num=${isnum%%.*}

But using a more efficient implementation won't change the net result of
your script, at least on systems where echo -e does what you wanted.

>             add_num=`expr $int_num + 1 1>/dev/null 2>&1`

This line sets add_num to the empty string (because there is no output
from expr).  Why run a command substitution if there won't be any output?
Also, your lack of shell quoting could cause you grief; it would be more
robust to use "$int_num" rather than $int_num.  The following is similar
to your above line, but safer:

add_num=
expr "$int_num" + 1 >/dev/null 2>&1
kms=$?

And even more efficiently, you can get the same results without forking,
by following my earlier advice:

case $int_num in
  *[!0-9]*) kms=1; echo non-numeric;;
  *) kms=0; echo numeric;;
esac

But again, switching to a more efficient implementation shouldn't seem to
have any bearing on your results.

>      kms=$?
>            # if [ "$?" -ne "0" ]
>              if [ "$kms" -ne "0" ]
>             then
>             log_msg "Debug msg4.new1 File has expr pstat $kms int_num is
>     $int_num"

Well, I don't see anything obvious about why you are seeing this:

> Debug msg3.1 File FILE1 has int_num1 28 has ps 0
> Debug msg4.new1 File has expr pstat 51198 int_num is 28
...
> Debug msg3.1 File  FILE2 has int_num1 1  has ps 0

then again, you post-formatted the output, too (notice the inconsistent
spacing), and you didn't post the definition of log_msg.  So who knows
what else your post-formatting has changed, such that we aren't seeing
EXACTLY what happened to you.

But if it is a bug, then the bug is in your /bin/sh and not in expr.  And
if you really do have a buggy shell, then there's nothing this list can do
to help you.

> Is it because add_num=`expr $int_num + *1 1>/dev*/null 2>&1` whether i
> have to chanage it to
> add_num=`expr $int_num + *1 >*/dev/null 2>&1`?

The change between '>/dev/null' and '1>/dev/null' has no effect - they are
strictly equivalent in shell programming.  You may be benefited by doing
more homework on shell programming.  But so far, you have failed to show
any evidence of a bug in expr.  And inserting spurious * into the lines
doesn't make your example any easier to attempt and reproduce.

-- 
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden

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