[SOLVED] Shell Script Check for 2 lines Return?

khandu · 05-11-2014, 04:51 PM

Hi Guys

New to shell scripting..

I am trying to run a script which basically runs a command.. and if that command returns two lines then it does nothing.. but if it returns one line then it runs another command..

In other words, basically the script runs a command if it sees only one line return, if it sees more than one, do nothing.. (normally it will return only two lines)

I could capture the return status of the command but then it will always be true.. so that method won't work here..

How do I capture the fact that it has returned two lines and not one.. and so how do I modify this script below (I know it is wrong in itself in terms of rules)..

Code:

#!/bin/bash

ps -ef | grep script

if [ "$?" != "0" ]
run command

rknichols · 05-11-2014, 04:58 PM

Code:

if [ $(ps -ef | grep script | wc -l) = 2 ]; then
    # Run command
fi

khandu · 05-11-2014, 05:01 PM

Quote:

Originally Posted by rknichols

Code:

if [ $(ps -ef | grep script | wc -l) = 2 ]; then
    # Run command
fi

DOH... didn't think of wc -l.. dumb of me .. so simple..

Thanks, will test it out

khandu · 05-11-2014, 05:06 PM

Quote:

Originally Posted by rknichols

Code:

if [ $(ps -ef | grep script | wc -l) = 2 ]; then
    # Run command
fi

I am getting this error

Quote:

./check.sh: line 3: [: missing `]'

Code:

#!/bin/bash

if [ $(ps -ef | grep script | wc -l) = 1]; then
echo "sudo /etc/init.d/script restart"
fi

rknichols · 05-11-2014, 05:08 PM

That closing "]" needs to be a separate "word", preceded by a space.

khandu · 05-11-2014, 05:35 PM

Quote:

Originally Posted by rknichols

That closing "]" needs to be a separate "word", preceded by a space.

Thanks .. was probably trying to do it in a hurry to fix an issue

jlinkels · 05-11-2014, 06:33 PM

"a = b" is not a valid numeric comparison in bash. "a -eq b" is.

jlinkels

ntubski · 05-11-2014, 07:08 PM

Are you checking for 2 lines because the ps returns the grep itself in addition to the script? Use pgrep, it's made to solve this exact problem:

Code:

if pgrep -f script ; then
  run command...
fi

rknichols · 05-11-2014, 08:22 PM

Quote:

Originally Posted by jlinkels

"a = b" is not a valid numeric comparison in bash. "a -eq b" is.

jlinkels

This is a place where testing two strings for equality is perfectly valid and is all that is needed.

khandu · 05-11-2014, 09:59 PM

Thanks guys

So for some reason the equality is not working for me..

If I do

if pgrep -f script ; then
fixcommand

How do i make it do the then statement when pgrep does not return something.. because since the script is running it should not do anything

Something like

khandu · 05-11-2014, 10:15 PM

is this a good idea??

Code:

if [ -z `pgrep service` ] ; then
restart service

grail · 05-12-2014, 03:56 AM

You seem to be over-complicating things a bit. The if is testing for success, so if pgrep returns something it will execute your new command. As you actually want the opposite of this you will
need to negate the outcome supplied to if.

Also, as pgrep outputs to the console and you are not interested in the output (only if there is any), I would suggest redirecting the output to /dev/null

ntubski · 05-12-2014, 10:34 AM

Oh, I didn't notice you were checking if the script wasn't running. Like grail said, you need to negate the condition:

Code:

if ! pgrep -f script ; then
...