pattern without ^ and $ matches nothing unless Surrounded

[starius]

1. There are two functions called Matches.
   • from pire/run.h:

bool Matches(const Scanner& scanner, const char* begin, const char* end)
{
        return Runner(scanner).Run(begin, end);
}

• from README:

bool Matches(const Pire::NonrelocScanner& scanner, const char* ptr, size_t len)
{
        return Pire::Runner(scanner)
                .Begin()        // '^'
                .Run(ptr, len)  // the text 
                .End();         // '$'
                // implicitly cast to bool
}

Which one is correct?

If Begin() and End() are to be called, then patterns without ^ and $ match nothing:

When Begin() is called, it feeds scanner with special begin char, moving it to dead state 1.

Compare this graph with the graph produced for same pattern surrounded and optimised:

Does this mean that all patterns must begin with ^ and end with $? Are Begin() and End() calls required? It should be clarified and documented.

2 . pigrep

Program pigrep behaves as latter Matches, calling Begin() and End(). It also surrounds its patterns. I have removed surrounding (btw it would be useful option, grep has it as -x, --line-regexp) and get the following results:

$ echo -n 'abc' | pigrep 'abc'
$ echo -n 'abc' | pigrep '^abc'
$ echo -n 'abc' | pigrep 'abc$'
$ echo -n 'abc' | pigrep '^abc$'
abc

Summary of problems here:

• pattern without ^ and $ matches nothing unless Surrounded
• two different functions called Matches
• provide pigrep option equivalent to grep --line-regexp