Perl One Liner

Today I had to add a list of users to a service (knowbe4). I could have done it manually but I decided to use Perl to do it which (I think) made me gain a lot of time.

Instead of checking the current subscribed users, see which one to delete and which one to add manually (would have taken a lot of time since there are a lot of users already and even more users to add).

The format for to_add.csv was like this:

First Name,Second Name,Email Address

So here I share the one liner I came up with:

perl -ne 'chomp;/,([^,]+)$/;$#ARGV==0 ? $keep{lc $1}=$_ :exists $keep{lc $_} ? print $keep{lc $_},"\n" : warn $_, "\n"' to_add.csv already_in_mail 1>test_keep.csv 2>test_remove.csv

Here is how it works:

• perl -ne will read the files given in argument line by line (equivalent of while (<>))
• chomp remove the newline from the line
• /,([^,]+)$/ apply the regex to the line and capture the first group (mail address) into $1
• $#ARGV==0 check if its the first file given so to_add.csv
• if yes: $keep{lc $1}=$_ put the current line into a hash array and the mail is the key
• if not: exist $keep{lc $_} check if the mail exist
• if yes: it means we need to add/keep the mail to the service
• if not: (the mail is not in the to_add file) then we need to remove it I used print and warn to differentiate, so I redirect stdout for the user to add and stderr for the user to remove in their respective file.