awk script to extract the argument of an option

Question

Can some one explain what the awk '{for(i=1;i<=NF;i++) if($i~/-f/) print $(i+1)}') part does in the following snippet

line='/wwws/apache/apache2.4.16w-r01/instroot/bin/httpd -f /www/csbe-int-fb-na/generated/httpd.conf -C ServerName int-b2vusii.bmwgroup.net -c PidFile /var/tmp/apache_csbe-int-fb-na/httpd.pid'
CONF=$(echo $line | awk '{for(i=1;i<=NF;i++) if($i~/-f/) print $(i+1)}')

O/p : /www/csbe-int-fb-na/generated/httpd.conf -C

but i need to get only /www/csbe-int-fb-na/generated/httpd.conf

Answer 1

I've reformatted the awk code:

    for(i=1;i<=NF;i++)
        if($i~/-f/)
            print $(i+1)

The for-loop iterates from 1 to NF, the number of fields in any input line.

Each field ($i) in the input line gets checked to see if it matches the pattern "-f", which is just a string literal.

If a field matches "-f", then the code prints out the field following the field that contains "-f".

On my a RHEL box, this ends up printing out:

/www/csbe-int-fb-na/generated/httpd.conf -C

If you look closely at the input line, there's a field that consists exactly of "-f", and indeed, awk prints out the next field, "/www/csbe-int-fb-na/generated/httpd.conf" Confusingly, that field contains an embedded "-f", so on the next iteration of the for-loop, the awk script finds taht "/www/csbe-int-fb-na/generated/httpd.conf" contains "-f", so it prints the next field, "-C".

If all you want is the Apache configuration file, you can modify the pattern that the field must match to make it an exact match, and have the awk script quit after finding the "-f" field, and printing the next field.

awk '{for(i=1;i<=NF;i++)if($i~/^-f$/) {print $(i+1); exit} }'