Perhaps sed was not meant to be a programming language, but there is a limited form of flow control. Adding some features common in other languages to sed would facilitate solving some problems and perhaps make sed more readable. Here are features I would like to see in an improved sed or a "trans sed".

• global macros - sed supports macros within a regular expression and within a substitute command. These are \1 through \9 and are defined by previously placed pairs of escaped parentheses. A formal global macro definition would reduce the overall length and size of larger sed scripts.
• global integer variables would facilitate counting and enumeration of substitutions within the actual substitution.
• a way to compare the "hold" and "pattern" spaces and then "branch" equal and not equal
• the ability to branch on substitution or on no substitution for the substitute command
• the ability to branch on match or branch on no match for an "address" (which may be a regular expression.) This command would immediately follow a pair of braces.