In appreciation of bare (naked) double-D(ashes)
Today I was trying to grep through a directory structure full of PHP code, looking for a function which, inexplicably, returned
Grepping for anything with a dash as not as easy as one would think, since grep assumes the
- indicates a command argument, and just pauses, waiting for further input, like this:
[davidy:~/tmp] 130 % grep -6 stupid-php-files/* ^C [davidy:~/tmp] 130 % grep "-6" stupid-php-files/* ^C
No problem, I figured, I’ll just escape the dash. But nope, no, and na-da:
[davidy:~/tmp] 130 % grep \-6 stupid-php-files/* ^C
Bare double dash does do the deed!
Finally, Google leads me on a journey of discovery of “bare double dashes”.
It turns out, a double-dash (
--) indicates to the built-in bash commands that we’re done with command options, allowing the
-6 to be searched for as a plain string:
[davidy:~/tmp] 130 % grep -- -6 stupid-php-files/* return(-6); # because stupid [davidy:~/tmp] %
What about brackets?
What about grepping for open/closing brackets? (hi, @tjh)
Turns out that is just as simple as escaping the bracket, as illustrated below:
[davidy:~/tmp] % grep (because stupid-php-files/* zsh: unknown file attribute: b [davidy:~/tmp] 1 % grep \(because stupid-php-files/* (because I can) [davidy:~/tmp] %
Practical test ?
When I shared my new, groundbreaking discovery, one of my colleagues pointed out that the following is therefore completely safe (while at the same time quite terrifying):
rf -- -rf /
To prove it (yes, I tested on
[davidy:~/tmp] 1 % rm -- -rf / rm: -rf: No such file or directory rm: /: is a directory [davidy:~/tmp] 1 %