Using grep in a for loop

Question

I'm trying to write a for loop with grep. When grep returns a value I want to display the message "running". If no value is returned then display "available".

I think there is something is wrong with my if statement, but I can't find anything.

Any suggestions would be greatly appreciated.

    #!/bin/sh
    #JWR1.0, REL1.10

    echo "Content-type: text/html"
    echo ""

    chk_port = 'ps -ef | grep "port $i -"'

    for (( i=1; i<=5; i++ ))
    do
            if [[ $chk_port ]]; then
                    echo "Running - $i<br>"
            else
                    echo "Available - $i<br>"
            fi
    done

    echo "<br>"

    # For debugging


    ps -ef | grep "port 1 -"

Sample output:

    Available - 1
    Available - 2
    Available - 3
    Available - 4
    Available - 5

    apache 7706 7700 0 15:07 ? 00:00:00 grep port 1 -

Try replacing $chk_port with this: $(ps -ef | grep "port $i -") — ed.
– ed., Commented Jul 22, 2013 at 22:27
@ed.: That makes the for-loop rather pointless, since it just checks five times to see if the process was originally running . . . — ruakh
– ruakh, Commented Jul 22, 2013 at 22:55
@ed.: Oh, I see; you're not suggesting to set chk_port to $(ps -ef | grep "port $i -"), you're suggesting to dispense with $chk_port and instead use $(ps -ef | grep "port $i -"). O.K., yes, good. :-) — ruakh
– ruakh, Commented Jul 22, 2013 at 23:20

Kent · Accepted Answer · 2013-07-22 22:31:51Z

1

I guess your problem is, there is no port $i in your ps's output, but your script thinks it exists.

The problem is, the command grep port $i - is also in ps -ef's output, it was clear in your debugging output. You can test it with ps -ef|grep foo

To avoid it, there is a trick, just do

chk_port=$(ps -ef | grep "[p]ort $i -")

for example:

kent$  ps -ef|grep nothing  
kent     10226  4752  0 00:36 pts/2    00:00:00 grep --color=auto nothing

kent$  ps -ef|grep [n]othing
zsh: no matches found: [n]othing

Also you could check the return code of grep (grep -q) to decide if the pattern was found. If no matches found, grep returns 1, otherwise 0.

answered Jul 22, 2013 at 22:31

Kent

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