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Shell script to check a command executed sucessfully or not


 
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# 1  
Shell script to check a command executed sucessfully or not

Hi All,


I am trying to write a shell script to check if a command executed successfully or not in rhel 7 and finding the installed tomcat version.


I am using below script.


Code:
var4=$(find / -name "catalina.jar" ! -size 0 |egrep -v "tmp|docker|WinSxS|Permission|HISTORY|alternatives|bearer11ssl|manifest")

i=`which java`


for loc4 in $var4
do

abc=`$i -classpath $loc4 org.apache.catalina.util.ServerInfo`
xyz="$abc"
status=$?
if [ $status -eq 0 ];then
 #   tomcat_version=`grep -w "Server number:" $xyz`
  #$xyz > /tmp/tomcat
  echo -e "{\"'tomcat'\":\"'"$xyz"'\"}"
fi

done



But when i am trying to execute script it's displaying the output info even if the command not executed successfully.




Output :



Code:
Error: Could not find or load main class org.apache.catalina.util.ServerInfo
{"'tomcat'":"''"}
{"'tomcat'":"'Server version: Apache Tomcat/9.0.30 Server built: Dec 7 2019 16:42:04 UTC Server number: 9.0.30.0 OS Name: Linux OS Version: 3.10.0-1062.9.1.el7.x86_64 Architecture: amd64 JVM Version: 1.8.0_171-b11 JVM Vendor: Oracle Corporation'"}


Last edited by Scrutinizer; 01-29-2020 at 05:03 PM..
# 2  
Hi,

Looking at this snippet:
Code:
xyz="$abc"
status=$?

$? will always be true (0) since the previous command is xyz="$abc" which is a variable assignment, which will always be successful..
# 3  
Hi Scrutinizer,


Thanks for the reply.


if $abc executed successfully then only i want to print that output.
# 4  
Quote:
Originally Posted by sravani25
...
if $abc executed successfully then only i want to print that output.
$abc can't be executed as it is a variable holding the result of the "command substitution". If you want to check if that was OK, move the status assignment one up, then:


Code:
abc=`$i -classpath $loc4 org.apache.catalina.util.ServerInfo`
status=$?
xyz="$abc"

# 5  
It might be that you are not getting output but actually it is errors being displayed. Standard output (good things you want to see) are written to file descriptor 1. Standard errors (bad things that you usually want to see) are written to file descriptor 2. Both of these are usually directed to the screen, but I think you are wanting to ignore some of them.

You might try directing your error output elsewhere. Some examples of this could be:-
Code:
some_command  2>  /tmp/error_file    # Save the errors to this file
some_command  2>  /dev/null          #  Actually I don't care, just bin them
some_command  2>  &1                 # Redirect errors to standard output

This last one can be useful if you want to consider the messages returned.


Does that get you moving?




Kind regards,
Robin
# 6  
Hi rbatte1 and Rudi,


Thanks for the reply.

My intention is when ever I run the below command, if the output is successful then I want to print successful output need to ignore if the command output is not successfull.
Code:
$i -classpath $loc4 org.apache.catalina.util.ServerInfo

But I tried to redirect the output but still getting error messages.
Code:
Error: Could not find or load main class org.apache.catalina.util.ServerInfo
{"'tomcat'":"'Server version: Apache Tomcat/9.0.30 Server built: Dec 7 2019 16:42:04 UTC Server number: 9.0.30.0 OS Name: Linux OS Version: 3.10.0-1062.9.1.el7.x86_64 Architecture: amd64 JVM Version: 1.8.0_171-b11 JVM Vendor: Oracle Corporation'"}


Moderator's Comments:
Mod Comment
Please wrap all code, files, input & output/errors in CODE tags.
It makes them easier to read and preserves spacing for indenting or fixed-width data.

Last edited by rbatte1; 02-06-2020 at 06:19 AM..
# 7  
Can you show us how you tried to redirect the output?

Please wrap your commands and the output in CODE tags. To do this, you can simply highlight your text that is code or data and then click on the </> in the editing menu. (You can also type code tags [code] and [/code] by hand.)






Robin

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