UNIX for Advanced & Expert Users

#!/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> _

#!/bin/ksh
# alt_o2b.sh
# This has not been tested by ShellCheck and runs under sh, bash, and ksh!

# 256 bytes of octal values from 000 to 377.
split_octal="000001002003004005006007010011012013014015016017
020021022023024025026027030031032033034035036037040041042043044045046047
050051052053054055056057060061062063064065066067070071072073074075076077
100101102103104105106107110111112113114115116117120121122123124125126127
130131132133134135136137140141142143144145146147150151152153154155156157
160161162163164165166167170171172173174175176177200201202203204205206207
210211212213214215216217220221222223224225226227230231232233234235236237
240241242243244245246247250251252253254255256257260261262263264265266267
270271272273274275276277300301302303304305306307310311312313314315316317
320321322323324325326327330331332333334335336337340341342343344345346347
350351352353354355356357360361362363364365366367370371372373374375376377"

binary()
{
	printf '%s\n' $split_octal | while read octal
	do
		# Obtain octal string length.
		length="${#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#"${subtext1%???}"}
			# Convert to pure binary.
			printf '%b' "\0$subtext2"
			# Increment values needed.
			position=$(( position + 3 ))
			ooo=$ooo'???'
		done
	done
}

binary > /tmp/binary2

# The line below is just for checking...
hexdump -C /tmp/binary2

exit 0

binary () 
{ 
    printf '%s\n' $1 | while read octal; do
        while [ "${#octal}" -gt 0 ]; do
            subtx=${octal%"${octal#???}"};
            octal=${octal#"${subtx}"};
            printf '%b' "\0$subtx";
        done;
    done
}

binary() { 
    while read octal
    do
        while [ "${#octal}" -gt 0 ]
        do
            subtx=${octal%"${octal#???}"}
            octal=${octal#"${subtx}"}
            printf '%b' "\0$subtx"
        done
    done
}

printf '%s\n' $split_octal | binary > output_file

binary < input_file > output_file

00
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
10
11
12
13
14
15
16
17
18
19
1A
1B
1C
1D
1E
1F

xxd -r -p file | hd
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