The main advantages of precompiling chunks are: faster loading, protecting source code from user changes, and off-line syntax checking.
Pre-compiling does not imply faster execution because in Lua chunks are always compiled into bytecodes before being executed. luac simply allows those bytecodes to be saved in a file for later execution.
luac produces a single output file containing the bytecodes for all source files given. By default, the output file is named luac.out, but you can change this with the -o option.
The binary files created by luac are portable to all architectures with the same word size. This means that binary files created on a 32-bit platform (such as Intel) can be read without change in another 32-bit platform (such as Sparc), even if the byte order (``endianness'') is different. On the other hand, binary files created on a 16-bit platform cannot be read in a 32-bit platform, nor vice-versa.
In the command line, you can mix text files containing Lua source and binary files containing precompiled chunks. This is useful to combine several precompiled chunks, even from different (but compatible) platforms, into a single precompiled chunk.
You can use "-" to indicate the standard input as a source file and "--" to signal the end of options (that is, all remaining arguments will be treated as files even if they start with "-").
The internal format of the binary files produced by luac is likely to change when a new version of Lua is released. So, save the source files of all Lua programs that you precompile.
-l produce a listing of the compiled bytecode for Lua's virtual machine. Listing bytecodes is useful to learn about Lua's virtual machine. If no files are given, then luac loads luac.out and lists its contents.
-o "file" output to file, instead of the default luac.out. The output file may be a source file because all files are loaded before the output file is written. Be careful not to overwrite precious files.
-p load files but do not generate any output file. Used mainly for syntax checking and for testing precompiled chunks: corrupted files will probably generate errors when loaded. Lua always performs a thorough integrity test on precompiled chunks. Bytecode that passes this test is completely safe, in the sense that it will not break the interpreter. However, there is no guarantee that such code does anything sensible. (None can be given, because the halting problem is unsolvable.) If no files are given, then luac loads luac.out and tests its contents. No messages are displayed if the file passes the integrity test.
-s strip debug information before writing the output file. This saves some space in very large chunks, but if errors occur when running these chunks, then the error messages may not contain the full information they usually do (line numbers and names of locals are lost).
-v show version information.
luac.out default output file