# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/([+]*)([0-9]+)(([,])([0-9]+))*/$2${3:+.$5:}/gm;t' <<< "+000123,456
+123
000123,456
123
+123.45
-123,45"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html