Re: Bash bug?
From: Zoltan Boszormenyi (zboszor_at_freemail.hu)
Date: 09/26/05
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Date: Mon, 26 Sep 2005 07:36:46 +0200 To: For users of Fedora Core releases <fedora-list@redhat.com>
Zoltan Boszormenyi írta:
> Hi,
>
> I am trying something like the following,
> with a configuration file containing a token and
> a directory in a line, depending on the tokens,
> certain actions should be taken later. Validating
> the configuration file whether all the required/optional
> tokens are in the file should go like this:
>
> -----a.txt----------------------
> A directory1
> B directory2
> C directory3
> --------------------------------
>
> -----a.sh-----------------------
> #!/bin/bash
>
> HAS_A=0
> HAS_B=0
> HAS_C=0
> cat a.txt | while read i ; do
> if [ "`echo $i | awk '{ print $1 }'`" = "A" ]; then
> HAS_A=1
> fi
> if [ "`echo $i | awk '{ print $1 }'`" = "B" ]; then
> HAS_B=1
> fi
> if [ "`echo $i | awk '{ print $1 }'`" = "C" ]; then
> HAS_C=1
> fi
> echo "A: $HAS_A B: $HAS_B C: $HAS_C"
> done
> echo "Final A: $HAS_A B: $HAS_B C: $HAS_C"
> --------------------------------
>
> Result is:
>
> --------------------------------
> $ ./a.sh
> A: 1 B: 0 C: 0
> A: 1 B: 1 C: 0
> A: 1 B: 1 C: 1
> Final A: 0 B: 0 C: 0
> --------------------------------
>
> It seems to be a bug to me, the envvars lose their values
> they gained in the loop. It's an ancient bug I must add,
> I just rechecked it and bash in RedHat 7.1 behaves the same.
> How can I preserve the variables' values? Putting "export"
> in front of every assignments doesn't help.
>
> Best regards,
> Zoltán Böszörményi
I just tried to narrow the test for the bug:
---b.sh-------------------------
#!/bin/bash
X=0
A=2
while [ $A -gt 0 ]; do
X=1
A=$(($A - 1))
echo "A: $A X: $X"
done
echo "Final A: $A X: $X"
--------------------------------
Result:
--------------------------------
$ ./b.sh
A: 1 X: 1
A: 0 X: 1
Final A: 0 X: 1
--------------------------------
The variables here keep their values. Hm. Then the bug may come
from the "cat a.txt | while read i; do" construct, maybe another
sub-shell is opened for this loop. But then putting "export"
in front of the assignments inside the loop should solve this but
it doesn't. It still seems to be a bug to me somewhere.
Can someone help me? Thanks in advance and best regards,
Zoltán Böszörményi
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