term% ls -F
term% pwd
term% cat index.txt
LEX(1)                      General Commands Manual                     LEX(1)

       lex - generator of lexical analysis programs

       lex [ -tvfn ] [ file ] ...

       Lex  generates  programs  to be used in simple lexical analyis of text.
       The input files (standard input default) contain regular expressions to
       be  searched  for, and actions written in C to be executed when expres‐
       sions are found.

       A C source program, `lex.yy.c' is generated, to be compiled thus:

              cc lex.yy.c -ll

       This program, when run, copies unrecognized portions of  the  input  to
       the  output,  and executes the associated C action for each regular ex‐
       pression that is recognized.

       The following lex program converts upper case to lower, removes  blanks
       at the end of lines, and replaces multiple blanks by single blanks.

              [A-Z] putchar(yytext[0]+'a'-'A');
              [ ]+$
              [ ]+  putchar(' ');

       The options have the following meanings.

       -t     Place  the  result  on  the  standard  output instead of in file

       -v     Print a one-line summary of statistics  of  the  generated  ana‐

       -n     Opposite of -v; -n is default.

       -f     `Faster' compilation: don't bother to pack the resulting tables;
              limited to small programs.

       M. E. Lesk and E. Schmidt, LEX - Lexical Analyzer Generator