lex & yacc, 2nd Edition

Appendix A. AT&T Lex

AT&T lex is the most common version found on UNIX systems. If you’re not sure which version of lex you have, try running a lexer through it with the -v flag. If the produces a terse two-line summary like this, it’s AT&T lex:

    5/2000 nodes(%e), 16/5000 positions(%p), 5/2500 (%n),
    4 transitions, 0/1000 packed char classes(%k), 6/5000
    packed transitions(%a), 113/5000 output slots(%o)

If produces a page of statistics with lex’s version number on the first line, it’s flex.

Lex processes a specification file and generates source code for a lexical analyzer. By convention, the specification file has a .l extension. The file that lex generates is named lex.yy.c.

The syntax of the AT&T lex command is:

lex [options] file

where options are as follows:

-c

Writes the lexer in C (default). The obsolescent flag is not present in many versions.

-n

Don’t print the summary line with the table sizes. This is the default unless the definition section changes the size of one of lex’s internal tables.

-r

Actions are written in RATFOR, a dialect of FORTRAN. This option no longer works in most versions of lex, and is not even present in many of them.

-t

Source code is sent to standard output instead of to the default file lex.yy.c. This is useful in Makefiles and shell scripts that direct the output of lex to a named file.

-v

Generates a one-line statistical summary of the finite state machine. This option is implied when any of the tables sizes are specified in the definitions section ...