Substring (Bidirectional Trim) Field Formatter

About

Trims content from the left or right from a set offset and an optional length as a full on Drupal field formatter.

I hadn't found a good way to trim from the left using the Drupal interface. The
PHP substr function seemed a good way to go about it, and there's some extra functionality to boot! For more advanced functionality and examples, read the official PHP documentation linked above. :)

Usage

There are two input fields, the first is the offset parameter and the second is length.

Offset Parameter

A negative value will trim all characters from the start of the string until
the specified character count from the end of the string (trimming from the
left), a positive value will do the opposite and trim from the right. For the
string "abcdef", 2 would output "cdef" and -2 would output "ef"'.

Length Parameter

Sets the string length to a fixed number of characters. For the string "abcdef"
, with a start/offset position of 2, a trim length of 1 would output "c" and a
trim length of -1 would output "cde".

Aside

For views you could use Twig 2's Slice Filter in a rewrite or global text field, there are instances where using a field formatter works smoother (passing information to Charts, Simple Math, etc). If this works for you you'd have one less contrib module installed, though things could get a little clunky!

I was playing around with having radio buttons for end/left, start/right direction, then having logic multiply by -1 to an absolute value of start - it might be a little more intuitive from a user standpoint, but it ended up being simpler just keeping it the same structure as the PHP function. If there's enough interest that could warrant an extra branch.