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, Dec 22 '16 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, Dec 22 '16 at 15:31

anubhava · Accepted Answer · 2016-12-22T15:31:33.280

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 '16 at 15:31

answered Dec 22 '16 at 15:26

anubhava

761,203
64
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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 – anubhava Dec 22 '16 at 15:30
1

That works now. Thank you. What can i google to better understand the "2>&1" at the end of the first line? – Happydevdays Dec 22 '16 at 15:35
`2>&1` redirects stderr to file descriptor `1` which is `stdout` – anubhava Dec 22 '16 at 15:37
1

@Happydevdays [The Linux Documentation Project](http://tldp.org/) is a great resource. [Beginner's guide](http://www.tldp.org/LDP/Bash-Beginners-Guide/html/Bash-Beginners-Guide.html). [Advanced guide](http://www.tldp.org/LDP/abs/html/abs-guide.html). And more specifically, [the I/O redirection topic you're asking about](http://www.tldp.org/LDP/abs/html/abs-guide.html#IO-REDIRECTION). – TTT Dec 22 '16 at 18:05
@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 – nmr Mar 23 '21 at 17:34

score 0 · Answer 2 · answered Dec 22 '16 at 15:29

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 '16 at 15:29

Farhad Farahi

35,528
7
73
70

score 0 · Answer 3 · answered Dec 23 '16 at 09:57

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 '16 at 09:57

jaiks

486
4
9

bash script - check for specific string in output is failing

3 Answers3

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