bash: "undefined variable" and pipe

nagaidhlig · #1 (**permalink**) 02-18-2008

Hi,
haven't found anything about this through searching, so may be a new topic:
when doing this:

set -o nounset
set -o errexit
find . -name "*.lib" | while read library; do
echo ${libary}
done
echo "after while"

I expect the script to exit within the while loop (because of nounset and the typo libary!=library). Actually, the script continues, probably because the pipe is executed in a subshell. But shouldn't the undefined variable error propagate up to the calling shell and trigger a non-zero exit?
Is there an option or way to force this?
Thanks in advance.

radoulov · #2 (**permalink**) 02-18-2008

[bash]

Code:

$ trap "echo I\'m out..." exit
$ set -o nounset -o errexit
$ find ./t -name "*.lib"|while read library; do echo $libary; done
bash: libary: unbound variable
$ while read library; do echo $libary; done< <(find ./t -name "*.lib")
bash: libary: unbound variable
I'm out...

nagaidhlig · #3 (**permalink**) 02-18-2008

Thanks for your answer, radoulov, but I'm not sure that's the solution, because the trap doesn't catch within the pipe, only when the script ends:

my script is called "b":
trap "echo I\'m out..." exit
set -o nounset -o errexit
find ./t -name "*.lib"|while read library; do echo $libary; done
echo the end

$ sh b
b: line 3: libary: unbound variable
the end
I'm out...

Anyway this would trap *all* exits, the good ones as well as the bad ones, which is not what I'm after. I want the script "b" to exit with a non-zero return value as soon as it's encountering the unbound variable, even befor the while loop is completed.

radoulov · #4 (**permalink**) 02-18-2008

The trap was only for the visual effect
the point was the process subsitution,
consider this:

Code:

% cat s
#!/bin/bash -ue

find ./t -name "*.lib"|while read library;do
  echo $libary
done

echo after the first loop # you'll see it

while read library;do
  echo $libary
done< <(find ./t -name "*.lib")

echo after the second one # you won't see it

ubuntux% ./s
./s: line 4: libary: unbound variable
after the first loop
./s: line 10: libary: unbound variable

chella · #5 (**permalink**) 02-18-2008

Hi,

Try this script. This may help you.

Code:

set -o nounset
#set -o errexit
find . -name "*.txt" | while read library; do
echo ${libary}
done
RC=$?  #return status of the previous command
if [ $RC -ne 0 ]
then
        exit
fi
echo "after while"

Regards,
Chella

nagaidhlig · #6 (**permalink**) 02-18-2008

Thanks chella, but your example only warns when you expect an error. My point was that an unsuspected "unbound variable" could get unnoticed.

radoulov, that works. I got a bit confused by the different behaviours of "./s" and "sh s" (the latter gives a syntax error).
Although, as I said, I was looking more for a setting that would raise an error with the existing code, rather than using a different construct, because when I know where to look, I can check unbound variables easily by hand.
Anyway, it probably is a feature in bash (not a bug) so I just have to be watchful.

Thank you very much again!

radoulov · #7 (**permalink**) 02-18-2008

Quote:

Originally Posted by nagaidhlig

Thanks chella, but your example only warns when you expect an error. My point was that an unsuspected "unbound variable" could get unnoticed.

radoulov, that works. I got a bit confused by the different behaviours of "./s" and "sh s" (the latter gives a syntax error).
Although, as I said, I was looking more for a setting that would raise an error with the existing code, rather than using a different construct, because when I know where to look, I can check unbound variables easily by hand.
Anyway, it probably is a feature in bash (not a bug) so I just have to be watchful.
[...]

I think you should understand the difference between sh command and
./command
(in the first case the shebang is only a comment):
Try changing the script like this:

Code:

% cat s
#!/bin/bash -ue
find ./t -name "*.lib"|while read correct;do
  echo $wrong
  echo $correct
done||exit

echo after the loop

% ./s
./s: line 3: wrong: unbound variable
% sh s

./t/1.lib
after the loop
% sh -ue s
s: 5: wrong: parameter not set

Consider this:

Code:

% cat s
#!/bin/bash -ue

find ./t -name "*.lib"|while read correct;do
  echo $wrong
  echo $correct
done

echo after the loop

% sh s

./t/1.lib
after the loop
% sh -uevx s
#!/bin/bash -ue

find ./t -name "*.lib"|while read correct;do
  echo $wrong
  echo $correct
done
+ find ./t -name *.lib
+ read correct
s: 1: wrong: parameter not set

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