sed

[Ruud H.G. van Tol]

GNU sed version 4.1.2
  Copyright (C) 2003 Free Software Foundation, Inc.
  This is free software; see the source for copying conditions.  There
is NO
  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE,
  to the extent permitted by law.

    $ echo some | /bin/sed -e 's/SOME/somephrase/I'
    somephrase

    $ echo som | /bin/sed -e 's/SOME/somephrase/I'
    Segmentation fault

    $ echo som | /bin/sed -e 's/SOME/somephrase/'
    som