Answer by David G for sed in-place flag that works both on Mac (BSD) and Linux

The following works for me on Linux and OS X:

sed -i''<expr> <file>

e.g. for a file f containing aaabbaaba

sed -i'''s/b/c/g' f

yields aaaccaaca on both Linux and Mac. Note there is a quoted string containing a space, with no space between the -i and the string. Single or double quotes both work.

On Linux I am using bash version 4.3.11 under Ubuntu 14.04.4 and on the Mac version 3.2.57 under OS X 10.11.4 El Capitan (Darwin 15.4.0).