Substr is a Statamic (v1) variable modifier that exposes PHP's substr function in your templates.

Substr accepts one or two integers and returns the resulting substring.

If {{ variable }} is set to output the string "This is text", this variable tag {{ variable|substr:2:-1 }} will output "his is tex".

A great way to use Substr is as a way to order entries loops by a select field. For example, imagine a select field which contains the days of the week. {{ entries:listing sort_by="day_of_week" }} will sort the resulting list alphabetically.

By adding a number to the beginning of each select item, you can sort by the day of the week.

day_of_week:
  type: select
  display: Day of the Week
  options:
    - 1 - Monday
    - 2 - Tuesday
    - 3 - Wednesday
    - 4 - Thursday
    - 5 - Friday
    - 6 - Saturday
    - 7 - Sunday

Using {{ day_of_week|substr:3 }} inside the entries loop will keep the output neat as "Monday, Tuesday" etc. instead of "1 - Monday, 2 - Tuesday" etc.

Note: This is the equivalent of {{ day_of_week|reverse|backspace:3|reverse }} which is a bit verbose.