Having worked on system programming for UNIX and a few of the PDP-11 DEC OS’s (DOS, RT, RSX, and in passing RSTS), I can tell you Fortran was abhorrent.

Sure it was the only high-level language I had on the RT and RSX systems, but its character handling was awful.    I ended up writing almost all that stuff in assembler

(which fortunately the PDP-11 is wonderful for).