Install Lex on Ubuntu 16.04. Lex is in flex and Yacc in bison.
sudo apt install flex bison
Create an empty file and edit it.
digit [0-9]
letter [A-Za-z]
%{
int count;
%}
%%
/* match identifier */
{letter}({letter}|{digit})* {count++; printf("number of identifiers = %d\n", count);}
%%
Save it as lol.l
lex lol.l gcc lex.yy.c -lfl
And we can run it by typing
./a.out
An example
