# icgrep > This is the open-source version of `icgrep 1.x` icgrep is a very fast regular expression search program, particularly for complex regular expressions. It is also a very capable engine, supporting most common regular expression syntax and many useful command line options. ### Usage `icgrep 1.0` is designed to offer substantial Unicode support, meeting **all** the Unicode Level 1 requirements of UTS #18, the Unicode Technical Standard for regular expressions. Development of `icgrep 2.0` is on track to meet the Unicode level 2 requirements of UTS #18. ##### Regex matching Normal usage to find lines in a file `f` matching a regular expression `r` is: `icgrep r f` ##### Counting matching lines To produce a count of matching lines only, use the flag `-c` such as below: `icgrep -c r f` To read the regular expression to be matched from file `regexpf` use the flag `-f` such as below: `icgrep -f regexpf f` ### Build `icgrep` is one of the tools available on `Parabix`. Check the [README.md](README.md) file for more information. ### License LLVM files are governed by the LLVM Release License in [LLVM-LICENSE.txt](LLVM-LICENSE.txt). `icgrep` is governed by Open Software License 3.0 in [OSL-3.0.txt](OSL-3.0.txt).