Hex to Binary conversion in bash

Question

I'm trying to convert a series of bytes from hex to bin using bash. but I keep getting (seemingly random) "(standard_in) 1: syntax error" replies from the following code:

for j in c4 97 91 8c 85 87 c4 90 8c 8d 9a 83 81
do
        BIN=$(echo "obase=2; ibase=16; $j" | bc )
        echo $BIN
done

I did a similar thing with dec to bin, which works perfectly fine:

for i in {0..120}
do
        KEYBIN=$(echo "obase=2; ibase=10; $i" | bc)
        echo $KEYBIN
done

Does anyone have an idea why it works with decimal, but not with hex? In my opinion the syntax is pretty much the same (unless I'm missing something really hard.)

Possible duplicate of [linux shell scripting: hex string to bytes](https://stackoverflow.com/questions/1604765/linux-shell-scripting-hex-string-to-bytes) — Ciro Santilli OurBigBook.com, Jun 17 '17 at 11:42

score 21 · Accepted Answer · answered Jun 20 '12 at 13:27

21

BC is a bit sensitive to case for hex values, change to uppercase and it should work

for j in C4 97 91 8C 85 87 C4 90 8C 8D 9A 83 81
do
        BIN=$(echo "obase=2; ibase=16; $j" | bc )
        echo $BIN
done

Output:

answered Jun 20 '12 at 13:27

Fredrik Pihl

44,604
7
83
130

so it really was a simple error. thank you for pointing this out, works like a charm. – fragman Jun 20 '12 at 16:44
glad to help, BC is a great tool with some quirks that you just have to know :-) – Fredrik Pihl Jun 21 '12 at 07:35
1

Does anybody know how to pad bc's output to a certain number of digits? This isn't needed in the example above, but just try the loop with a 00 as input. – Chaos_99 Mar 12 '13 at 14:16
have a look at the `length` function. "The value of the length function is the number of significant digits in the expression." – Fredrik Pihl Mar 12 '13 at 15:02
Here is an example with just one value: `echo "obase=2; ibase=16; EF" | bc` – Harsha Laxman May 18 '23 at 22:51

score 14 · Answer 2 · answered Nov 22 '19 at 16:20

14

I came up with this:

printf converts to hex, xxd -r -p takes the ascii hex stream and makes it actual binary

dumping with hexdump to prove it worked...

printf "%016x" 53687091200 | xxd -r -p | hexdump -C

answered Nov 22 '19 at 16:20

stu

8,461
18
74
112

Works. However, `xxd` won't let me combine `-r` and `-p` into `-rp`, and I can live with that for now. – Harry Apr 07 '23 at 11:37
how very un-unix like, but it is what it is I guess. you could open an issue on github probably :-) – stu Apr 08 '23 at 13:26

score 7 · Answer 3 · answered Jun 20 '12 at 13:31

Here's the script I use:

#!/bin/bash
# SCRIPT:  hex2binary.sh
# USAGE:   hex2binary.sh Hex_Number(s)
# PURPOSE: Hex to Binary Conversion. Takes input as command line
#          arguments.
#####################################################################
#                      Script Starts Here                           #
#####################################################################

if [ $# -eq 0 ]
then
    echo "Argument(s) not supplied "
    echo "Usage: hex2binary.sh hex_number(s)"
else
    echo -e "\033[1mHEX                 \t\t BINARY\033[0m"

    while [ $# -ne 0 ]
    do
        DecNum=`printf "%d" $1`
        Binary=
        Number=$DecNum

        while [ $DecNum -ne 0 ]
        do
            Bit=$(expr $DecNum % 2)
            Binary=$Bit$Binary
            DecNum=$(expr $DecNum / 2)
        done

        echo -e "$Number              \t\t $Binary"
        shift
        # Shifts command line arguments one step.Now $1 holds second argument
        unset Binary
    done

fi

Caveats: The hex numbers must be preceded by `0x`, and the **HEX** column actually lists decimal values. But thank you for offering a pure bash solution to a "How to ... in bash" question! Sometimes that's actually what people are looking for. You can't always depend on the presence of tools like bc. — system PAUSE, Aug 10 '15 at 06:30
the version of bash I am using (`4.4.12`) doesn't need to prefix the hex numbers. The script doesn't handle `0` correctly though, you want to replace `$Binary` with `${Binary:-0}` in the last `echo` call — untore, Feb 03 '18 at 11:39

score 2 · Answer 4 · edited Oct 13 '19 at 17:20

2

Try this:

for j in c4 97 91 8c 85 87 c4 90 8c 8d 9a 83 81
do
    BIN=$(echo "obase=2; ibase=16; ${j^^}" | bc )
    echo $BIN
done

edited Oct 13 '19 at 17:20

Jon

3,573
2
17
24

answered Oct 13 '19 at 14:52

zhwsh

31
1

There are other answers that provide the OP's question, and they were posted some time ago. When posting an answer [see: How do I write a good answer?](https://stackoverflow.com/help/how-to-answer), please make sure you add either a new solution, or a substantially better explanation, especially when answering older questions. – help-info.de Oct 13 '19 at 17:02
3

Accepted answer says uppercase is required and changes the input data. This answer keeps the data (that often is out of control) and instead uses `${j^^}` to convert the data to uppercase, thus this is the better solution, but lacking in explanation. – NiKiZe May 06 '22 at 06:19

Hex to Binary conversion in bash

4 Answers4

Linked