## SYNOPSIS

**blm firstfile [+afile] [-bfile] [%cfile] [\\&dfile] [@]...**

## DESCRIPTION

**blm**reads in one or more line-oriented files and considers each file as a set of strings. Blank lines do not represent the empty string, but instead are ignored. The first command line argument shown as firstfile above represents the starting set of lines. The arguments are then interpretted according to Forward Polish Notation (FPN), as described by Jan Lukasiewicz. Jan invented the first widely accepted non-classical logic as well as this excellent notation. FPN requires no parentheses to describe arbitrarily complex combinations of any number of binary operations.

Each successive command line argument after the first represents an operation that starts with the accumulator set A, applies the set operation A op B, and then stores the result in the accumulator A. Another set operation may then be performed until all listed arguments are used up. The result is then printed in lexicographical order to standard output. Four operations are supported: Set union is the plus symbol (+). Set intersection is the and symbol ( & ) which must be escaped in most shells. Set difference is the subtraction symbol (-). And set exclusive or is represented by the percent sign (%). There is also an optional shuffling symbol toggle, (@), that means to randomly shuffle all output lines instead of sorting in lexicographical order. Thus, a simple way to randomize lines in a file is as follows:

- blm firstfile @
- If a filename of "-" is listed, it represents the standard input to blm. If none of the four option characters appears at the beginning of a filename argument, set addition (+) is assumed.