Regular expression example in C++ and Qt Dependencies (on Debian bullseye) # apt-get install build-essential cmake qtbase5-dev Build git clone https://github.com/matthiasklein/regexp-cpp.git mkdir regexp-cpp-build cd regexp-cpp-build cmake ../regexp-cpp make Run ./app/replexp-cpp/replexp-cpp '#[A-Fa-f0-9]{6}' ./app/replexp-qt/replexp-qt '#[A-Fa-f0-9]{6}' Output #FFFFFF MATCH #FFFFFF from INPUT #FFFFFF #ffffff MATCH #ffffff from INPUT #ffffff #232323 MATCH #232323 from INPUT #232323 #abc #foobar #deadbeef MATCH #deadbe from INPUT #deadbeef #999