π in Bash
I think I'm pretty much doing pi approximations in every language now, so, here it is in the classic Linux shell: Bash!
Here are the other approximations so far:
Kotlin - https://repl.it/talk/share/p-in-Kotlin/36125
Ruby - https://repl.it/talk/share/p-in-Ruby/34982
Java - https://repl.it/talk/share/p-in-Java/34978
QBasic - https://repl.it/talk/share/p-in-QBasic/34973
Fortran - https://repl.it/talk/share/p-in-Fortran/34890
APL - https://repl.it/talk/share/p-in-APL/34888
Forth - https://repl.it/talk/share/p-in-Forth/34652
LOLCODE - https://repl.it/talk/share/p-in-LOLCODE/34421
Python and Node.js (Node is linked in post) - https://repl.it/talk/share/2-Approximations-of-p-In-Only-Four-Lines-of-Code/32773
C - https://repl.it/talk/share/p-Approximations-in-C/33461
Credit to @NoelBryan, @TheForArkLD , @Warhawk947 , and @LizFoster for inspiring these approximations. Most of these use the Nilakantha Series, although I also use the arctangent method (multiplying the radian arctangent of 1 by 4 to get pi and getting the arctangent with an infinite series) in three of them (Python, Node, and C).
Note: Bash is SLOW