#!/usr/local/bin/dash
# o2b.sh
# This passes ShellCheck and runs under dash!

# 256 bytes of octal values from 000 to 377.
octal="000001002003004005006007010011012013014015016017020021022023024025026027030031032033034035036037040041042043044045046047050051052053054055056057060061\
062063064065066067070071072073074075076077100101102103104105106107110111112113114115116117120121122123124125126127130131132133134135136137140141142143144145\
146147150151152153154155156157160161162163164165166167170171172173174175176177200201202203204205206207210211212213214215216217220221222223224225226227230231232\
233234235236237240241242243244245246247250251252253254255256257260261262263264265266267270271272273274275276277300301302303304305306307310311312313314315316317\
320321322323324325326327330331332333334335336337340341342343344345346347350351352353354355356357360361362363364365366367370371372373374375376377"

binary()
{
	# Obtain octal string length.
	length="${#octal}"
	# Subscript position starts at 1 NOT 0."
	position=1
	# 3 character octal value to be read.
	ooo="???"
	while [ "$position" -lt "$length" ]
	do
		# These two lines obtain the octal value.
		subtext1=${octal%"${octal#${ooo}}"}
		subtext2=${subtext1#"${subtext1%???}"}
		# Convert to pure binary.
		printf '%b' \\"$subtext2"
		# Increment values needed.
		position=$(( position + 3 ))
		ooo=$ooo'???'
	done
}

binary "$octal" > /tmp/binary

# The line below is just for checking...
hexdump -C /tmp/binary

exit 0

Last login: Sat Aug 27 22:02:46 on ttys000
AMIGA:barrywalker~> cd Desktop/Code/Shell
AMIGA:barrywalker~/Desktop/Code/Shell> ./o2b.sh
00000000  00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  |................|
00000010  10 11 12 13 14 15 16 17  18 19 1a 1b 1c 1d 1e 1f  |................|
00000020  20 21 22 23 24 25 26 27  28 29 2a 2b 2c 2d 2e 2f  | !"#$%&'()*+,-./|
00000030  30 31 32 33 34 35 36 37  38 39 3a 3b 3c 3d 3e 3f  |0123456789:;<=>?|
00000040  40 41 42 43 44 45 46 47  48 49 4a 4b 4c 4d 4e 4f  |@ABCDEFGHIJKLMNO|
00000050  50 51 52 53 54 55 56 57  58 59 5a 5b 5c 5d 5e 5f  |PQRSTUVWXYZ[\]^_|
00000060  60 61 62 63 64 65 66 67  68 69 6a 6b 6c 6d 6e 6f  |`abcdefghijklmno|
00000070  70 71 72 73 74 75 76 77  78 79 7a 7b 7c 7d 7e 7f  |pqrstuvwxyz{|}~.|
00000080  80 81 82 83 84 85 86 87  88 89 8a 8b 8c 8d 8e 8f  |................|
00000090  90 91 92 93 94 95 96 97  98 99 9a 9b 9c 9d 9e 9f  |................|
000000a0  a0 a1 a2 a3 a4 a5 a6 a7  a8 a9 aa ab ac ad ae af  |................|
000000b0  b0 b1 b2 b3 b4 b5 b6 b7  b8 b9 ba bb bc bd be bf  |................|
000000c0  c0 c1 c2 c3 c4 c5 c6 c7  c8 c9 ca cb cc cd ce cf  |................|
000000d0  d0 d1 d2 d3 d4 d5 d6 d7  d8 d9 da db dc dd de df  |................|
000000e0  e0 e1 e2 e3 e4 e5 e6 e7  e8 e9 ea eb ec ed ee ef  |................|
000000f0  f0 f1 f2 f3 f4 f5 f6 f7  f8 f9 fa fb fc fd fe ff  |................|
00000100
AMIGA:barrywalker~/Desktop/Code/Shell> _