#!/bin/bash

# Expands bash-style {} expressions.

# See <http://www.gnu.org/software/bash/manual/bash.html#Brace-Expansion>.

# Usage: [env expand_braces_debug=1] self <in >out

# Filters each line from stdin to stdout.

# Warning: Due to shell limitations, a blank line will be interpreted as EOF.

sedEreFlag="$(test "$(uname)" = Darwin && echo E || echo r)"

sed () { "$(which sed)" -"$sedEreFlag" "$@";}

echoEach () { local line; for line in "$@"; do echo "$line"; done; }

replaceRecursive ()

{

    local sedExpr="$1" str="$2" prevStr

    while true; do

        prevStr="$str"

        str="$(echo "$str"|sed -e "$sedExpr")"

        test "$str" = "$prevStr" && break # done if nothing replaced

    done

    echo "$str"

}

debug ()

{

    local label="$1" str="$2"

    test -n "$expand_braces_debug" && (echo "** $label:"; echo "$str") >&2

}

singleQuote="'"

singleQuoteEsc="'\''"

CR=$'\r'

LF=$'\n'

nonBracket="[^][]*" # matches non-[] chars

brackets="($nonBracket\[$nonBracket\])*$nonBracket"

while true; do

    read # get next line from stdin; strips trailing newlines

    line="$REPLY"

    test -z "$line" && break # EOF if no line or empty line

    line="${line//$CR/}" # remove \r

    origLine="$line"

    debug orig "$line"

    line="${line//$singleQuote/$singleQuoteEsc}" # escape single quotes

    line="$(echo "$line"|sed -e "s/[^{,}]+/'&'/g")" # escape non-brace chars

    # Escape commas inside [], which should not be used for {}.

    # Note that '' around "," are closing and opening the escaped string,

    # not the other way around.

    line="$(replaceRecursive "s/(\[$nonBracket)','/\1,/g" "$line")" # innermost

    # Also support one level of nesting, which is the most we currently use.

    line="$(replaceRecursive "s/(\[$brackets)','/\1,/g" "$line")" # 1st outer

    debug escaped "$line"

    debug expanded

    eval echoEach $line # brace-expand $line

done