Bash

Bash arrays are one dimensional variables. They may be one of two types, indexed or associative. Indexed arrays have integer keys and associative arrays have string keys. Values for both are strings. (Other languages call an associative array a “dictionary”, “hash”, or “map”.) Initializing Indexed arrays are declared using declare -a, but can also be implicitly declared (in the global scope) using ARRAY[subscript], where subscript is an arithmetic expression. For this reason, associative arrays must be explicitly declared using declare -A. Initial values may optionally be defined at declaration. The -p option to the declare builtin will print the full variable, including type, keys, and values. ...

A team member reported a problem with pre-commit hook I wrote, check-dns-serial, which ensures the SOA serial number is updated on any modified zone files. The script was giving them an error when they made a commit after the 8th revision in a day. It was an interesting bug in a bash script that I thought might be helpful to share. The serial number is, by convention, stored as a date string plus a 2-digit revision number. For example, 2021090104 would be today’s 4th change. This allows for 99 changes a day. The script splits this string (using cut) into two variables, the date and the revision. At one point, it checks to see if the old revision is already 99, to avoid an overflow. This is line that threw the error: ...