Languages that avoid manual memory management do it by having a
memory manager built into their runtime executable somewhere.
Typically, runtime environments in these languages are split into a
program part (the running script itself) and the interpreter part,
with the interpreter managing dynamic storage. On Unixes (and other
modern operating systems) the interpreter core can be shared by
multiple program parts, reducing the effective overhead for each
one.
Scripting is nowhere near a new idea
in the Unix world. As far back as the mid-1970s, in an era of far
smaller machines, the Unix shell (the interpreter for commands typed
to a Unix console) was designed as a full interpreted programming
language. It was common even then to write programs entirely in
shell, or
to use the shell to write glue logic that knit together canned
utilities and custom programs in C into wholes greater than the sum of
their parts. Classical introductions to the Unix environment (such as
The Unix Programming Environment [Kernighan-Pike84]) have dwelt
heavily on this tactic, and with good reason: it was one of Unix's
most important innovations.
Advanced shell programming mixes languages freely, employing
both binaries and interpreted elements from half a dozen or more
other languages for subtasks. Each language does what it does best,
each component is a module with narrow interfaces to the others,
and the global complexity of the whole is much lower than it would
be had it been coded as a single monster monolith in a general-purpose
language.
