The insane things people do in Bash sometimes...although I don't think anything can top the x86 Assembler that was written entirely in Bash:
http://lists.gnu.org/archive/html/bug-bash/2001-02/msg00054....
http://lists.gnu.org/archive/html/bug-bash/2001-02/msg00054....
it's a set of functions for bash that when sourced make the assembly a valid bash script which then runs and assembles itself. this is genius.
I don't really understand why the code works since I can't read x86 asm yet, but I think how it works is reasonably clear. Each instruction has its own bash function that writes its opcodes to the output file and the asm script to be assembled is (I think) sourced directly into the running shell session.
My favourite of the listed reasons.