`cat` using only bash built-ins, binary-safe (and extremely slow): while LANG=C IFS= read -rd $'\0' -n 1 a; do ([ -z "$a" ] && echo -ne '\x00' || echo -n "$a") ; done <input >output
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So at least Debian doesn not have the 'cat' builtin packaged. But if you build bash from source including the loadables, you can enable -f ~/src/bash/examples/loadables/cat cat See https://gitlab.com/gnuwget/wget2/wikis/Developer-hints:-Increasing-speed-of-GNU-toolchain … for instructions.
Interesting. Though if it's not there by default in typical distro it might as well not exist. The point of my snippet was for weird situations where you have to work with builtins only on an existing system :-)
