Convert HTML entities using AWK

convert-html-entities.sh

# hexadecimal reference to decimal
echo "--ƒ--" \
| awk '{ while (match($0, /&#x[0-9a-fA-F]+;/)) { n = "0x" substr($0, RSTART + 3, RLENGTH - 4 ); x = sprintf("&#%d;", strtonum(n)); $0 = substr($0, 1, RSTART - 1) x substr($0, RSTART + RLENGTH); }; print }'
--ƒ--

# decimal reference to character
echo "--ƒ--" \
| awk '{ while (match($0, /&#[0-9]+;/)) { n = substr($0, RSTART + 2, RLENGTH - 3 ); sub(/^0+/, "", n); x = sprintf("%c", strtonum(n)); $0 = substr($0, 1, RSTART - 1) x substr($0, RSTART + RLENGTH); }; print }'
--ƒ--

# hexadecimal to decimal and decimal to character
echo "--ƒ--" \
| awk '{ while (match($0, /&#x[0-9a-fA-F]+;/)) { n = "0x" substr($0, RSTART + 3, RLENGTH - 4 ); x = sprintf("&#%d;", strtonum(n)); $0 = substr($0, 1, RSTART - 1) x substr($0, RSTART + RLENGTH); }; print }' \
| awk '{ while (match($0, /&#[0-9]+;/)) { n = substr($0, RSTART + 2, RLENGTH - 3 ); sub(/^0+/, "", n); x = sprintf("%c", strtonum(n)); $0 = substr($0, 1, RSTART - 1) x substr($0, RSTART + RLENGTH); }; print }'
--ƒ--