Perl one liner to extract LUNid and disk alias from /etc/multipath.conf file

Introduction:

We may run into situations wherein we need to fetch the LUN id and alias mapping for disks under multipath on a Linux machine. Obtaining this data manually would prove to be cumbersome. One way to fetch this data would be to use the combination of grep and paste commands. But I felt that my Perl was getting a bit rusty so I decided to go the Perl way.

First take a look at the entries from the sample file.

        multipath {
                wwid                    36000d3100008f20000000000000001f4
                alias                   dvd-rhel5-2-64
        }
        multipath {
                wwid                    36000d3100008f20000000000000001f6
                alias                   dvd-rhel5-2-32
        }
        multipath {
                wwid                    36000d3100008f20000000000000003e2
                alias                   dvd-rhel4-7-32
        }

The above output shows the multipath stanzas for a couple of disks. We are basically interested in the wwid and alias section. To extract the required information we will be using the below combination of two Perl one liners.

[root@sahil-lab1 ~]# cat mpath.cf  | perl -ne 'print if(/wwid|alias/);' | perl -pne 'if($.%2){s/\n/\t/;}'

                wwid                    36000d3100008f2000000000000000356                       alias                   aleppo

                wwid                    36000d3100008f2000000000000000a3a                       alias                   dc2tst

                wwid                    36000d3100008f2000000000000000b02                       alias                   dc1tst

                wwid                    36000d3100008f20000000000000003cf                       alias                   algiers

                wwid                    36000d3100008f2000000000000000397                       alias                   algiers_local

                wwid                    36000d3100008f200000000000000004b                       alias                   chicago

                wwid                    36000d3100008f200000000000000004c                       alias                   chicago_mysql

                wwid                    36000d3100008f200000000000000004d                       alias                   chicago_local

                wwid                    36000d3100008f200000000000000004e                       alias                   chicago_assets

                wwid                    36000d3100008f20000000000000001f4                       alias                   dvd-rhel5-2-64

                wwid                    36000d3100008f20000000000000001f6                       alias                   dvd-rhel5-2-32

                wwid                    36000d3100008f20000000000000003e2                               alias                   dvd-rhel4-7-32

[root@sahil-lab1 ~]#

You could further add an additional Perl one liner to print only the alias and LUN id as shown below.

[root@sahil-lab1~]# cat mpath.cf  | perl -ne 'print if(/wwid|alias/);' | perl -pne 'if($.%2){s/\n/\t/;}' | perl -F"\s+" -lane 'print "$F[4]  $F[2]"' 

 aleppo  36000d3100008f2000000000000000356

dc2tst  36000d3100008f2000000000000000a3a

dc1tst  36000d3100008f2000000000000000b02

algiers  36000d3100008f20000000000000003cf

algiers_local  36000d3100008f2000000000000000397

chicago  36000d3100008f200000000000000004b

chicago_mysql  36000d3100008f200000000000000004c

chicago_local  36000d3100008f200000000000000004d

chicago_assets  36000d3100008f200000000000000004e

dvd-rhel5-2-64  36000d3100008f20000000000000001f4

dvd-rhel5-2-32  36000d3100008f20000000000000001f6

dvd-rhel4-7-32  36000d3100008f20000000000000003e2

[root@sahil-lab1~]#

Explanation:

The first one liner simply prints lines containing the strings wwid or alias.

The next one liner loops over the content piped from the previous one liner and uses $. variable denoting the line number. If the remainder of the division of the line number by 2 is not 0 i,e. the line is odd, then the new line after the end of the line gets replaced by a tab thereby combining the even and odd numbered lines together. 

The last one liner invokes the awk like functionality available with Perl one liners. The -F flag in conjunction with -a flag allow us to split lines based on a delimiter and the individual strings in the line get stored in an array variable named @F and we can extract the fields by using the scalar elements that make up the @F array.

Conclusion:

I'm sure there are easier and perhaps more compact versions of Perl one liners out there to accomplish this task. I would appreciate any suggestions and feedback on this approach of extracting the required fields from the /etc/multipath.conf file.