bashc
A hacked up version of GNU bash that supports a "compiler" mode wherein instead of executing commands, it generates equivalent C code. Only a small subset of bash's language features are supported. There are no variables or substitutions, but pipes and basic control flow constructs should work.
While very primitive, it is capable of a funny little bootstrap maneuver with which you can use this shell-to-C compiler to (in combination with a C compiler) create a native executable that acts as a shell-to-native-code compiler:
$ cat compiler.sh
./bash --compile /dev/stdout /dev/stdin | gcc -xc - -xnone libbashc.o
$ ./bash compiler.sh < compiler.sh
$ mv a.out shtoelf
$ echo '/bin/echo hello world' | ./shtoelf
$ ./a.out
hello world
Note that the resulting executable has no runtime dependency on bash
itself; it performs its own fork, execve, pipe (etc.) calls to
execute the commands in the compiled script directly.
To build a compilation-enabled bash:
$ autoconf configure.ac > configure
$ ./configure --enable-compiler
$ make
The resulting bash binary's --compile flag (which can also be
abbreviated -X) takes an output file as its argument.
(This hack was originally based on version 4.1 of bash, and only recently rebased onto a newer upstream.)