Simple example on Lex programming. What is lex? Lex is a programming tool on UNIX platform,takes the tokens as a input in the form of regular expression and generates the c routine called as lexer.
● Lexer is also called as lexical analyser.
Tokens:
Tokens are nothing but primitives of any programming language. It can be constants,keywords,expressions,identifiers etc. Tokens can be the combination of alphabets, digits or any metacharacters. [Note: metacharacters are special symbols like *, $ etc].
Regular expression : It is a powerful mechanism to describe the tokens.
Lexical Analyser:
It is a initial program for the compiler, which reads theinput character by character and converts them into meaningful sequence.
How To Execute Lex Program?
● Open any text editor( Alternatively you can open it using terminal; type gedit filename.l ).
● Type your program and save it using “.l” extension.
● Open terminal(Ctrl+Alt+T).
● Type 1. $ lex filename.l 2. $ cc lex.yy.c -ll 3. $ ./a.out
● It will dispaly the output. Press Ctrl+d to see output[optional].