Yes, UNIX was written in C in a terminal to start with.

While UNIX is "native" C at the core, you can develop useful small to medium applications with Unix tools called from inside shell scripts or one line commands - from the terminal. shell == DCL, except what you can do in UNIX is an extreme superset of that because of tools like awk grep and sed. Entire applications are written in shell. There are also a lot of interpreted languages that let you do things like develop modest db apps in shell or performs extended precision calculations <- examples.

DCL is verbose; shell cryptic and terse... It is possible to write one line of code that does what 20 lines of DCL might do. And a lot harder for beginners to read.

The one thing you will have to learn is regular expressions to get the most out of unix tools. Another concept is processes. Unix creates lots of child processes, sometimes each command is a separate child. This affects variable scope.

Your default shell is probably bash - consider googling for 'Advanced bash guide' and see how you fare with it. Assuming you were okay with DCL.