topic Re: Testing in Bourne shell vs POSIX shell in Operating System - Linux

Testing in Bourne shell vs POSIX shell

renarios — Thu, 22 Sep 2005 04:10:55 GMT

Hi all,

I have yet another Bourne shell vs POSIX shell question.

In a script I check the database status using the following statements:

# Check database status
STATUS=$(sqlplus -s </ as sysdba
set heading off feedback off
select status from v\$instance;
exit
EOF)

Now my question is:
When I test using the Bourne shell all works fine (see example 1), bur when I test the POSIX (preferred) way, it fails.

#example1
if [ ${STATUS} = "OPEN" ]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"$STATUS
exit
fi
The database started successfully!

#example2
if [[ ${STATUS} = "OPEN" ]]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"$STATUS
exit
fi
Database NOT open, status is: OPEN

An echo \'${STATUS}\' returns ' OPEN'
An echo \'"${STATUS}"\' returns '
OPEN'

What is the best way to use the POSIX testing method (and make working)

Thanks in advance,

Renarios

Re: Testing in Bourne shell vs POSIX shell

Muthukumar_5 — Thu, 22 Sep 2005 04:17:05 GMT

What are you getting on ${STATUS} Variable in both shells. Try as,

# Check database status
STATUS=$(sqlplus -s </ as sysdba
set heading off feedback off
select status from v\$instance;
exit
EOF)
echo ${STATUS}

Execute and revert with results.

Good scripting is as,

if [[ "${STATUS}" = "OPEN" ]]

hth.

Re: Testing in Bourne shell vs POSIX shell

renarios — Thu, 22 Sep 2005 04:33:35 GMT

Hi hth,
here are the results:
$>$STATUS=$(sqlplus -s <> / as sysdba
> set heading off feedback off
> select status from v\$instance;
> exit
> EOF)
$>echo ${STATUS}
OPEN

The problem still exists:
if [[ "${STATUS}" = "OPEN" ]]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"$STATUS
fi
Database NOT open, status is: OPEN

$>echo \'${STATUS}\'
' OPEN'
$>echo \'"${STATUS}"\'
'
OPEN'

If I test using if [[ "${STATUS}" = ' OPEN' ]] it also doesn't work

Any more ideas?

Cheers,
Renarios

Re: Testing in Bourne shell vs POSIX shell

Muthukumar_5 — Thu, 22 Sep 2005 04:48:35 GMT

After getting ${STATUS} variable do like,

echo ${STATUS} | od -dc

Change the check statement like,

if [ $(echo $STATUS | grep 'OPEN') = "OPEN" ]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"$STATUS
fi

# Note: Don't use exit when executing shell statements with script.

BTW: I am Muthukumar (hth - hope this helps)

hth.

Re: Testing in Bourne shell vs POSIX shell

renarios — Thu, 22 Sep 2005 06:12:29 GMT

Ehhhm whoops, sorry Muthukumar.

The "echo ${STATUS} | od -dc" returns the following:

echo ${STATUS} | od -dc
0000000 20304 17742 02560
O P E N \n
0000005

I didn't write the script myself, I'm only checking it on errors and rewriting it to POSIX. The exits in the script is another issue, but we'll solve that.
The option you gave is a good one.
Is there an option to use for the creation of the STATUS variable?
I know an option like:
# Remove leading CR/LF
status=$(echo ${STATUS} | cut -c 1-)
But that's very quick and dirty. Is there another way for that?

Thanks,

Renarios

Re: Testing in Bourne shell vs POSIX shell

VEL_1 — Thu, 22 Sep 2005 06:17:41 GMT

Hi,

To remove CR

str=$(echo $str| tr -d '\r\032')

To remove LF

str=$(echo $str | tr -d '\r')

Re: Testing in Bourne shell vs POSIX shell

VEL_1 — Thu, 22 Sep 2005 06:20:58 GMT

Sorry for confusing. try to use:

sed 's/^M$//'

Re: Testing in Bourne shell vs POSIX shell

Muthukumar_5 — Thu, 22 Sep 2005 06:21:35 GMT

I am not sure with od -dc output. It is correct as,

# echo 'OPEN' | od -dc
0000000 20304 17742 02560
O P E N \n
0000005

Actually It is not good to get "STRING" as return value in shell scripting (my idea)!!. Try to use number for that easily as,

# Check database status
STATUS=$(sqlplus -s </ as sysdba
set heading off feedback off
select status from v\$instance;
exit
EOF) | grep -q 'OPEN'

if [ $? -eq 0 ]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"$STATUS
exit
fi
# END

$? is the variable returns value of the previous command execution. I am requesting you to use it. Use like $? or ${?}

May be problem with sh binary? Don't know.

hth.

Re: Testing in Bourne shell vs POSIX shell

Ralph Grothe — Thu, 22 Sep 2005 06:36:42 GMT

As for the stripping of line feeds proposed by raj,
afaik, the Unix line feed is \n or \012
(man ascii), so the transliteration should in my opinion read

echo "$STATUS" | tr -d \\012

Besides, there isn't such big difference between the HP Posix Shell and the Bash.
You could as well avoid word splitting in Bash in your test blocks by usage of the twin square brackets
e.g.
if [[ $STATUS = OPEN ]]; then ...

Re: Testing in Bourne shell vs POSIX shell

Bill Hassell — Thu, 22 Sep 2005 07:06:06 GMT

Are you actually using the Bourne shell to test? In HP-UX, the Bourne shell is found in /usr/old/bin/sh and unless you specify the desired interpreter (shell) as your first line, the script will be run by whatever shell you are using at the moment. Always code the interpreter:

#/usr/old/bin/sh

or

#/usr/bin/sh

And just like with Bourne, POSIX, Korn and BASH, you can trace the execution with set -x or run the script with the interpreter and the -x flag as in:

/usr/old/bin/sh -x myscript

Note that tracing is always sent to stderr so to pipe everything into more or pg, redirect stderr:

/usr/bin/sh -x myscript 2>&1 | more

As far as the OPEN not working, the result of the program is TWO lines, not one. Although octal it's a pain to read, it's clear that your sqlplus program returns a blank line followed by OPEN. So there are several ways to solve this:

STATUS=$(echo "$STATUS | tail -1)

but this suffers from the prblem that the sqlplu program may be unstable (not dependable to always write a blank line), so just use grep:

if echo "$STATUS" | grep -q OPEN
then
echo "Database is OPEN"
else
echo "Database not open, status is \""$STATUS"\""
fi

(note the use of extra " in the not-open status--it will delimit the beginning and end of the actual string)

BTW: A much, much easier way to decode strings is to use hex:

echo "$STATUS" | xd -xc

Note that od and xd are the same program, so you can also use this:

echo "$STATUS" | od -xc

Re: Testing in Bourne shell vs POSIX shell

renarios — Thu, 22 Sep 2005 07:27:50 GMT

Hi Bill,
Since this script is executed by user oracle (non-root) I always code using the interpreter #!/usr/bin/sh. Is that correct?

I will use the following in my script (which according my information is correct POSIX ):
STATUS=$(echo $(sqlplus -s </ as sysdba
set heading off feedback off
select status from v\$instance;
exit
EOF) | tr -d \\012)

# Use double brackets (My favorit)
if [[ ${STATUS} = "OPEN" ]]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"${STATUS}
#exit <-- rewrite to return


fi   

Cheerio,

Renarios

Re: Testing in Bourne shell vs POSIX shell

Bill Hassell — Thu, 22 Sep 2005 11:44:48 GMT

Correct. The standard shell for HP-UX is the POSIX shell and is found in /usr/bin/sh. Unfortunately, this is exactly the same name used in other Unix flavors for the Bourne shell, thus endless confusion. It's really hard to find Bourne to POSIX shell conversion problems. Korn and Bash are also POSIX compliant shells so they more than 95% identical.

Re: Testing in Bourne shell vs POSIX shell

Gregory Fruth — Thu, 22 Sep 2005 12:35:14 GMT

Perhaps you could just change the test to
[[ "$STATUS" = "OPEN\n" ]].

The thing I don't understand is how the
trailing newline is getting in there in the
first place. The $() construct is supposed to
strip it: (from the man page)

The standard output from a command enclosed in
parenthesis preceded by a dollar sign ($(...))
or a pair of grave accents (`...`) can be used
as part or all of a word; trailing newlines are
removed.

Re: Testing in Bourne shell vs POSIX shell

Arturo Galbiati — Fri, 23 Sep 2005 03:01:08 GMT

Hi renarios,
the problem is not related to teh shell, but to Oracle. You disable the header putting head off but not the new page. Instead of head off use pages 0 and SQL will retrun the status withou any control char:

Your code:
09:58 GPOP09BN hpbbnn1/home/oracle/> STATUS=$(sqlplus -s <> / as sysdba
> set head off feedback off
> select status from v\$instance;
> exit
> EOF)
10:00 GPOP09BN hpbbnn1/home/oracle/> echo "$STATUS"

OPEN
10:00 GPOP09BN hpbbnn1/home/oracle/>

my code:

10:01 GPOP09BN hpbbnn1/home/oracle/> STATUS=$(sqlplus -s <> / as sysdba
> set pages 0 feedback off
> select status from v\$instance;
> exit
> EOF)
10:01 GPOP09BN hpbbnn1/home/oracle/> echo "$STATUS"
OPEN
10:01 GPOP09BN hpbbnn1/home/oracle/>

This fix your problem about test.
Art

Re: Testing in Bourne shell vs POSIX shell

Muthukumar_5 — Fri, 23 Sep 2005 03:05:30 GMT

Art,

Check this on following the execution of sql as,

if [[ ${STATUS} = "OPEN" ]]
then
echo "The database started successfully!"
else
echo "Database NOT open, status is:"$STATUS
exit
fi

You have to get "The database started successfully!" on getting ${STATUS} on POSIX shell.

Try it and post result.

hth.

Re: Testing in Bourne shell vs POSIX shell

Arturo Galbiati — Fri, 23 Sep 2005 03:08:25 GMT

10:08 GPOP09BN hpbbnn1/home/oracle/> if [[ ${STATUS} = "OPEN" ]]
> then
> echo "The database started successfully!"
> else
> echo "Database NOT open, status is:"$STATUS
> exit
> fi
The database started successfully!
10:09 GPOP09BN hpbbnn1/home/oracle/>

Art

Re: Testing in Bourne shell vs POSIX shell

renarios — Fri, 23 Sep 2005 03:24:50 GMT

Thanks Bill, for the feedback. It meens I was informed correctly!

Gregory, I already tried your test scenario, but that failed. I 'll dive into the man pages again.

Art, You scored the lot! That was solution on my issue.

Solution the reply from Art!

Thanks to all who assisted me on this issue.

Cheerio,

Renarios