in TC17 32 bits, from rootfs.gz, in /etc/init.d/tc-functions:
the functions merge(), replace(), purge() use the commands index() and getline. but I think they are not functional because they are not internal into ash, neither applets from busybox. Also /bin/which did not find them.
I tested by: I booted in GUI from qemu, and opened aterm then sourced /etc/init.d/tc-functions.