This question already has answers here:
Base 64 encoding from command line gives different output than other methods
(2 answers)
Closed 7 days ago.
Can anyone explain this?
[vagrant#centos ~]$ echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64
MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo=
[vagrant#centos ~]$ echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -d
10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm
The first string encodes with o= at the end, but the encoded string with == at the end instead, decodes to the same original string...
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
Compare these
echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64 | od -c
echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -D | od -c
echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo=" | base64 -D | od -c
If we don't send the newline when using echo the o is missing, have a look at this...
echo -n "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64
It's the newline that's being encoded that gives the o in o=
The = is padding and it might not always be there. Have a look here..
https://en.wikipedia.org/wiki/Base64#Padding
Different implementations may also use different padding characters. You can see some of the differences here
https://en.wikipedia.org/wiki/Base64#Variants_summary_table
From the RFC
3.2. Padding of Encoded Data
In some circumstances, the use of padding ("=") in base-encoded
data is not required or used. In the general case, when
assumptions about the size of transported data cannot be made,
padding is required to yield correct decoded data.
Implementations MUST include appropriate pad characters at the end
of encoded data unless the specification referring to this document
explicitly states otherwise.
The base64 and base32 alphabets use padding, as described below in
sections 4 and 6, but the base16 alphabet does not need it; see
section 8.
When you use $echo, a newline is appended to the end of the output. This newline character is part of the base64 encoding. When you change the 'o' to a '=', you're changing the encoding of the newline character. In this case, the character it decodes to is still not a printable character.
In my terminal, decoding the two string yields the same output, but the string ending in "o=" has a newline, and the string ending in "==" does not.
$> echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo=" | base64 -d
10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm
$> echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -d
10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm $>
Using $echo -n would allow you to pass the string into base64 without the trailing newline. The string without the newline encodes to the string ending in "==".
On Macs, I noticed I had to append "\c" to the end of my string to get it to work, like this:
[vagrant#centos ~]$ echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm\c" | base64
The result was:
MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbVxjCg==
PHP also encodes it properly, which leads me to believe there is some issue with the base64 program in bash, as I haven't found any mention of 'o' somehow being used as a padding character.
php > echo base64_encode("10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm");
MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==
Related
I've been experiencing some weird issues today while debugging, and I've managed to trace this to something I overlooked at first.
Take a look at the outputs of these two commands:
root#test:~# printf '%X' 10 | xxd -r -p | xxd -p
root#test:~# printf '%X' 43 | xxd -r -p | xxd -p
2b
root#test:~#
The first xxd command converts hex to ASCII. The second converts ASCII back to hex. (43 decimal = 2b hex).
Unfortunately, it seems that converting hex to ASCII does not preserve non-printable characters. For example, the raw hex "A" (10 decimal = A hex), somehow gets eaten up by xxd -r -p. Thus, when I perform the inverse operation, I get an empty result.
What I am trying to do is feed some data into minimodem. I need to generate Call Waiting Caller ID (FSK), effectively via bit banging. My bash script has the right bits, but if I do a hexdump, the non-printable characters are missing. Unfortunately, it seem that minimodem only accepts ASCII characters, and I need to feed it raw hex, but it seems that gets eaten up in the conversion. Is it possible to preserve these characters somehow? I don't see it as any option, so wondering if there's a better way.
xxd expects two characters per byte. One A is invalid. Do:
printf '%02X' 10 | xxd -r -p | xxd -p
How to convert hex to ASCII while preserving non-printable characters
Use xxd. If your input has one character, pad it with an initial 0.
ASCII does not preserve non-printable characters
It does preserve any bytes, xxd is the common tool to work with any binary data in shell.
Is it possible to preserve these characters somehow?
Yes - input sequence of two characters per byte to xxd.
I am trying to make a bash script work on MinGW and it seems the shell is not able to decode something like the following.
t=$(openssl rand -base64 64)
echo "$t" | base64 --decode
Resulting in,
Ԋ7▒%
▒7▒SUfX▒L:o<x▒▒䈏ţ94V▒▒▒▒uW;▒▒pxu▒base64: invalid input
Interestingly, if I output the base64 character and run the command as such, it works.
echo "+e5dcWsijZ83uR2cuKxIDJTTiwTvqB7J0EJ63paJdzGomQxw9BhfPvFTkdKP9I1o
g29pZKjUfDO8/SUNt+idWQ==" | base64 --decode
Anybody knows what I am doing wrong?
Thanks
I solved the above case by passing --ignore-garbage flag to the base64 decode. It ignores the non-alphabet characters.
echo "$t" | base64 --decode --ignore-garbage
However, I would still like to know how did I create "garbage" ;) ?
I think what has happened here is the base64 string contains some embedded spaces, and that causes the actual "invalid input" w (and what you observe to as garbage.)
The openssl rand -base64 64 command introduces some newlines (not spaces), for example,
openssl rand -base64 64 > b64.txt
... then viewing the b64.txt file in an editor I see two separate lines
tPKqKPbH5LkGu13KR6zDdJOBpUGD4pAqS6wKGS32EOyJaK0AmTG4da3fDuOI4T+k
abInqlQcH5k7k9ZVEzv8FA==
... and this implies there is a newline character between the 'k' and 'a'
So the base64 string has this embedded newline. The base64 -d can handle newlines (as demonstrated by your successful example), but, it cannot handle space char.
The newlines can get translated to spaces by some actions of the shell. This is very likely happening by the echo $t I.e. if t has newlines inside it, then echo will just replace then with single space. Actually, how it behaves can depend on shell options, and type of string quotes, if any, applied.
To fix the command, we can remove the newline before piping to the base64 -d command.
One way to do that is to use tr command, e.g. the following works on Linux:
t=$(openssl rand -base64 64 | tr -d '\n')
echo $t | base64 -d
... or alternatively, remove the spaces, again using tr
t=$(openssl rand -base64 64)
echo $t | tr -d ' ' | base64 -d
This question already has answers here:
Conversion hex string into ascii in bash command line
(7 answers)
Closed 3 years ago.
I need to output a symbol using variable that contains code of that symbol.
I already understood that in my code example bash thinks that i'm giving it a string. So according to specificator it outputs "4".
symbolValue=41
printf '%c' $symbolValue
I expect outputing of "A" symbol in fixed code. Please help me with it.
Could you please try the following.
symbolValue=41
echo "$symbolValue" | xxd -p -r
# OR
xxd -p -r <<< "$symbolValue"
From man xxd:
-p | -ps | -postscript | -plain
output in postscript continuous hexdump style. Also known as
plain hexdump style.
-r | -revert
reverse operation: convert (or patch) hexdump into binary. If
not writing to stdout, xxd writes into its output file without
truncating it. Use the combination -r -p to read plain hexadecimal
dumps without line number information and without a particular
column layout. Additional Whitespace and line-breaks are
allowed anywhere.
If I base64 encode a string which consists of seven characters e.g. abcdefg with the website https://www.base64encode.org/ the result is YWJjZGVmZw==. The trailing "==" characters are padding because the number of input characters cannot be divided by 7.
I've to reproduce this result in bash. So I've tried the following command:
echo "abcdefg" | base64
However, the result is different now:
YWJjZGVmZwo=
I'm using Ubuntu where base64 (GNU coreutils) 8.25 is installed.
I would be glad if someone could give me a hint.
I've just noticed that the reason for the described behaviour is the newline which echo writes at the end. So the correct command is the following which suppress the newline
echo -n "abcdefg" | base64
Then the output is like I expect it:
YWJjZGVmZw==
It is also tricky how a here-string will produce unexpected output. It is probably missing the null character \0.
$ base64 <<<"abcdefg"
YWJjZGVmZwo=
$ printf 'abcdefg' | base64
YWJjZGVmZw==
What's the best way to read and convert a JSON field's decimal value to an ASCII character? For instance, converting 107 to 'k'. The manual doesn't appear to mention a direct way to do so.
$ jq -n '[107] | implode'
"k"
implode will work for both ASCII and non-ASCII decimal codes. As illustrated here, it converts an array of admissible decimals to a UTF-8 string equivalent.
Here's an example showing conversion:
$ jq -n -c '{"a": [107, 108]} | .a |= implode'
{"a":"kl"}