Re: [PATCH 2/3] dfa: new option DFA_STRAY_BACKSLASH_WARN

[Bruno Haible]

Paul Eggert wrote:
> This is for grep, which wants to warn about stray backslashes that
> lead to unspecified behavior.  For example, "grep -oi '\a'"
> surprisingly is not equivalent to "grep -oi 'a'", so the stray
> backslash should be warned about.

This warning punishes a traditional habit, namely to backslash-escape
a leading ASCII '-' character, so as to avoid it from being interpreted
as an option.

Suppose I want to search for an ASCII arrow in some text:

$ echo xy | ./grep '->'
./grep: invalid option -- '>'
Usage: grep [OPTION]... PATTERNS [FILE]...
Try 'grep --help' for more information.

Decades ago, I was taught that the workaround is to add a backslash.
This now produces

$ echo xy | ./grep '\->'
./grep: warning: stray \ before -

To avoid the warning, now I would have to write:

$ echo xy | ./grep '[-]>'

This is more cumbersome, because I have to insert two characters at
different positions, rather than just one character.

Bruno