s6-portable-utils
Software
skarnet.org
s6-expr evaluates an expression and writes the result to stdout.
s6-expr expression...
s6-expr acts as the generic expr utility, except that the : operator (pattern matching) is not supported.
s6-expr accepts an arbitrary number of arguments.
s6-expr is not suitable as a Single Unix expr program; however, if you are never using the pattern matching functionality, s6-expr scrupulously follows the rest of the specification.