Ascii/Hex convert in bash

Question

I'm now doing it this way:

[root@~]# echo Aa|hexdump -v
0000000 6141 000a                              
0000003
[root@~]# echo -e "\x41\x41\x41\x41"
AAAA

But it's not exactly behaving as I wanted,

the hex form of Aa should be 4161,but the output is 6141 000a,which seems not making sense.

and when performing hex to ascii,is there another utility so that I don't need the prefix \x ?

Solution 1

The reason is because hexdump by default prints out 16-bit integers, not bytes. If your system has them, hd (or hexdump -C) or xxd will provide less surprising outputs - if not, od -t x1 is a POSIX-standard way to get byte-by-byte hex output. You can use od -t x1c to show both the byte hex values and the corresponding letters.

If you have xxd (which ships with vim), you can use xxd -r to convert back from hex (from the same format xxd produces). If you just have plain hex (just the '4161', which is produced by xxd -p) you can use xxd -r -p to convert back.

Solution 2

For the first part, try

echo Aa | od -t x1

It prints byte-by-byte

$ echo Aa | od -t x1
0000000 41 61 0a
0000003

The 0a is the implicit newline that echo produces.

Use echo -n or printf instead.

$ printf Aa | od -t x1
0000000 41 61
0000002

Solution 3

$> printf "%x%x\n" "'A" "'a"
4161

Solution 4

For single line solution:

echo "Hello World" | xxd -ps -c 200 | tr -d '\n'

It will print:

48656c6c6f20576f726c640a

or for files:

cat /path/to/file | xxd -ps -c 200 | tr -d '\n'

For reverse operation:

echo '48656c6c6f20576f726c640a' | xxd -ps -r

It will print:

Hello World

Solution 5

With bash :

a=abcdefghij    
for ((i=0;i<${#a};i++));do printf %02X \'${a:$i:1};done

6162636465666768696A

View more solutions

Comments

[gdb]

How to convert hex back to ascii?

[gdb]

xxd -p -r AAA,this doesn't work,can it retrieve parameters from command line directly?

[Random832]

no... and the 'r' converts back from hex, you'd want something like 'echo 4161 | xxd -r -p' or 'echo Aa | xxd -p'

[SourceSeeker]

@gdb: See printf where it says: "If the leading character is a single-quote or double-quote, the value shall be the numeric value in the underlying codeset of the character following the single-quote or double-quote."

[Yokai]

python != bash

[jcomeau_ictx]

neither are sed, hexdump, printf, awk, or xxd.

[jcomeau_ictx]

it's shorter than some of the other solutions and arguably more readable. and it converts both ways, from the Bash command line. I don't see your point.

[Giac]

wrong output for some characters like (space, tab, \r,\n) all of these characters will be shown as \x00

[Yokai]

The point is, he asked for a bash solution. Meaning, as per his context, bashisms or bash built-ins. You didn't provide this with python solution(s).

[Yokai]

The c-style printf solution here should be the accepted answer. It is the most portable and the most simple, and keeps with POSIX compliance without needing external tools that may or may not be available.

[Casey Flynn]

echo -n "Hello, world!" | xxd -ps -c 200 would also work

[ssc]

I typically use xxd -ps -c 200 <<< "Hello, world!"

[cary]

example: echo -e "\x68"