Grep 
Unix shorthand for the command line g/re/p, or "global-regular expression-print." A grep tool lets programmers search through a set of text files for a pattern called the regular expression, which is a syntax that lets you specify in great detail what kind of text you're looking for. Grep tools are used, for example, to find and replace variable names or look for patterns such as a social security number. While originally a Unix tool, there are now grep tools on virtually every platform.