Approximation of the grammar for Bash braces expressions

braces.lark

start       : brace+
brace       : [preamble] expandable [postscript]

preamble    : /[^{}]+/
postscript  : /[^{}]+/

expandable  : "{" (range | list) "}"

range       : begin ".." end [".." step]
begin       : BOUND
end         : BOUND
step        : SIGNED_INT

list        : [item] ("," [item])+
item        : /[^{},]+/ | brace+

BOUND       : LETTER | SIGNED_INT
%import common.LETTER
%import common.SIGNED_INT

// https://www.gnu.org/software/bash/manual/html_node/Brace-Expansion.html
// TODO
// Escaped "{", "}", ","
// ${}
// Unicode

Try it at https://lark-parser.github.io/ide/#