base58 broke on bash 5.2.21 on cygwin 2.932

[wetbits]

bash reports a syntax issue :
$ [[ 666F6FC7ADE88F =~ ^(0{2})([[:xdigit:]]{2}) ]]
$ echo $?
2

Removing the {2}s is a workaround:
[[ $REPLY =~ ^(0*)([[:xdigit:]]*) ]]

bitcoin-bash-tools/bitcoin.sh

Line 151 in 8661db2

[[ $REPLY =~ ^(0{2}*)([[:xdigit:]]{2}*) ]]

[grondilu]

I can't reproduce this on Fedora 41

$ [[ 666F6FC7ADE88F =~ ^(0{2})([[:xdigit:]]{2}) ]] ; echo $?
1
$ echo $BASH_VERSION
5.2.26(1)-release

The curly brace notation here is a bound, as described in regex(7), which bash should conform to by default, if I'm not mistaken. I don't why it would be different on cygwin.

[wetbits]

Sorry, I left out the '*'s in my example.
What I meant to write (like line 151):

[[ 666F6FC7ADE88F =~ ^(0{2}*)([[:xdigit:]]{2}*) ]] 

After rolling up my sleeves, I found Cygwin not only reports syntax but also provides a different answer.

cygwin (5.2.21(1)-release):

$ [[ 666F6FC7ADE88F =~ ^(0{2}*)([[:xdigit:]]{2}*) ]]
$ echo $\?=$? 0=${BASH_REMATCH[0]} 1=${BASH_REMATCH[1]} 2=${BASH_REMATCH[2]} 3=${BASH_REMATCH[3]} 4=${BASH_REMATCH[4]}
$?=2 0=666F6FC7ADE88F 1= 2= 3=666F6FC7ADE88F 4=8F

Instead of the expected (Linux 4.4.302+ / bash 4.4.23(1)-release):

$?=0 0=666F6FC7ADE88F 1= 2=666F6FC7ADE88F 3= 4=

The issue is forming a "piece" by following an "atom" with both a bound and '*'.
Regex (7) excerpt: "A piece is an atom possibly followed by a single(!) '*', '+', '?', or bound."

A fix would be to add '(' and ')' around the piece to form another atom like:

$ [[ 666F6FC7ADE88F =~ ^((0{2})*)(([[:xdigit:]]{2})*) ]]

this gives consistent output on cygwin and linux (at least mine).

$?=0 0=666F6FC7ADE88F 1= 2= 3=666F6FC7ADE88F 4=8F

Of course, you would have to adjust your use of BASH_REMATCH[n] to ensure that you reference the n you want.

David

[grondilu]

You are correct that a piece is not supposed to be followed by either '*', '+' etc. So it may actually be cygwin which is right here.

I'm not too keen on adding parenthesis as they add captures but this may be the only correct way to do it unfortunately. Non capturing groups (?: ... ) are not supported in bash.

I may use grep instead.

[wetbits]

I'm happy to see you crossed out the grep instead! :)
You could also use a extglob like this:

shopt -s extglob
In=000123
Right=${In#+(00)}; Left=${In%$Right}
echo Left=$Left Right=$Right

Left is any 00 (zero pairs), and Right is the rest.
If you want to verify it's hex, you can

${Right//[^0-9a-fA-f]}

Or if you want to check and not correct, you can compare the fixed version

[ "$In" = "$Left$Right" ] ...