FOSS World News: Fun with Mail Merge and Cool Bash Arrays

Monday, March 25, 2019

Fun with Mail Merge and Cool Bash Arrays

Creating a sed-based file substitution tool.

A few weeks ago, I was digging through my spam folder and found an email message that started out like this:


Dear #name#
Congratulations on winning the $15.7 million lottery payout!
To learn how to claim your winnings, please...

Obviously, it was a scam (does anyone actually fall for these?), but what captured my attention was the #name# sequence. Clearly that was a fail on the part of the sender who presumably didn't know how to use AnnoyingSpamTool 1.3 or whatever the heck he or she was using.

The more general notation for bulk email and file transformations is pretty interesting, however. There are plenty of legitimate reasons to use this sort of substitution, ranging from email newsletters (like the one I send every week from AskDaveTaylor.com—check it out!) to stockholder announcements and much more.

With that as the inspiration, let's build a tool that offers just this capability.

The simple version will be a 1:1 substitution, so #name# becomes, say, "Rick Deckard", while #first# might be "Rick" and #last# might be "Deckard". Let's build on that, but let's start small.

Simple Word Substitution in Linux

There are plenty of ways to tackle the word substitution from the command line, ranging from Perl to awk, but here I'm using the original UNIX command sed (stream editor) designed for exactly this purpose. General notation for a substitution is s/old/new/, and if you tack on a g at the end, it matches every occurrence on a line, not only the first, so the full command is s/old/new/g.

Before going further, here's a simple document that has necessary substitutions embedded:


$ cat convertme.txt
#date#

Dear #name#, I wanted to start by again thanking you for your
generous donation of #amount# in #month#. We couldn't do our
work without support from humans like you, #first#.

This year we're looking at some unexpected expenses,
particularly in Sector 5, which encompasses #state#, as you
know. I'm hoping you can start the year with an additional
contribution? Even #suggested# would be tremendously helpful.

Thanks for your ongoing support. With regards,

Rick Deckard
Society for the Prevention of Cruelty to Replicants

Scan through it, and you'll see there's a lot of substitutions to do: #date#, #name#, #amount#, #month#, #first#, #state# and #suggested#. It turns out that #date# will be replaced with the current date, and #suggested# is one that'll be calculated as the letter is processed, but that's for a bit later, so stay tuned for that.

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