bash script - check for specific string in output is failing

Question

I have the following bash script:

#!/bin/sh
psql -U postgres -c "CREATE DATABASE test TEMPLATE template0;"

if [ $? -eq 0 ]; then
    echo OK
else
    if [ $? = 'ERROR:  database "test" already exists' ]; then
         echo OK
    else
         echo FAIL
    fi
fi

It's currently failing with the following error:

testbox:/tmp# sh test.sh 
ERROR:  database "test" already exists
FAIL

I'm not sure where I've gone wrong. I need it to return "OK" for this specific error. Any other errors should print out a FAIL. Can you tell me where I've gone wrong?

Thanks.

EDIT 1

I've modified the code to capture the output, not just rc:

#!/bin/bash

output=$(psql -U postgres -c "CREATE DATABASE test TEMPLATE template0;")
ret=$?

if [[ $ret -eq 0 ]]; then
    echo OK
else
    if [[ $output == 'ERROR:  database "test" already exists' ]]; then
         echo OK
    else
         echo FAIL
    fi
fi

But I get this error:

ERROR:  database "test" already exists
sh: ERROR:  database "test" already exists: unknown operand
FAIL

$? represents just the integer exit code not the output of your psql command. You need to grab the output and check. — anubhava
– anubhava, Commented Dec 22, 2016 at 15:22
@Happydevdays: try adding echo $? immediately after the psql command, and you'll see what anubhava means (it'll just print a number, probably "1"). Then add a second echo $?, and you'll see that one print "0" because the first echo command succeeded, and therefore exited with a status code of 0. — Gordon Davisson
– Gordon Davisson, Commented Dec 22, 2016 at 15:31

anubhava · Accepted Answer · 2016-12-22 15:31:33Z

5

$? represents just the integer exit code not the output of your psql command. You need to grab the output of psql command and check in if condition.

You can use:

#!/bin/bash

output=$(psql -U postgres -c "CREATE DATABASE test TEMPLATE template0;" 2>&1)
ret=$?

if [[ $ret -eq 0 ]]; then
    echo OK
else
    if [[ $output == *'already exists'* ]]; then
         echo OK
    else
         echo FAIL
    fi
fi

edited Dec 22, 2016 at 15:31

answered Dec 22, 2016 at 15:26

anubhava

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5 Comments

anubhava Over a year ago

I've changed first line to output=$(psql -U postgres -c "CREATE DATABASE test TEMPLATE template0;" 2>&1) so that we capture stderr also from psql command

Happydevdays Over a year ago

That works now. Thank you. What can i google to better understand the "2>&1" at the end of the first line?

anubhava Over a year ago

2>&1 redirects stderr to file descriptor 1 which is stdout

TTT Over a year ago

@Happydevdays The Linux Documentation Project is a great resource. Beginner's guide. Advanced guide. And more specifically, the I/O redirection topic you're asking about.

nmr Over a year ago

@anubhava I am having a similar issue but the return code is always 0 content=$(java -jar ${jarFilePath} -u ${username},${password} -n ${host} -c "${val_query}") rc=$? If the val_query has any syntax issue then how can I capture the error

Farhad Farahi · Accepted Answer · 2016-12-22 15:29:07Z

0

The $? will output an integer based on exit code of last command executed. when the database exists it will be 1 returned. Thats why your script is failing.

answered Dec 22, 2016 at 15:29

Farhad Farahi

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Comments

jaiks · Accepted Answer · 2016-12-23 09:57:24Z

0

A shorter way if checking if a database exists can be found here.

Based on that output you can create your database and return somehting meaningful.

answered Dec 23, 2016 at 9:57

jaiks

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