On 30/04/17 20:04, Bjørn Forsman wrote:
On 30 April 2017 at 19:53, Profpatsch <[email protected]> wrote:
On 17-04-30 03:07pm, Bjørn Forsman wrote:
On 30 April 2017 at 15:01, Bjørn Forsman <[email protected]> wrote:
Hi all,
I'm stuck trying to pass $'\t' to bash via Nix multi-line strings:
nix-repl> ''cut -d $'\t' -f 1''
error: syntax error, unexpected $undefined, expecting IND_STR or
DOLLAR_CURLY or IND_STRING_CLOSE, at (string):1:10
Oh, it was only missing double single-quotes before the dollar sign.
What tripped me was that the documentation says ${ is special in
strings, not $'.
How should we improve the manual in this regard?
Sure. But I'm also quite interested in knowing why $' needs escaping,
especially when $ ' (space between) does not.
I guess the answer resides at
https://github.com/NixOS/nix/blob/2f21d522c28b1e902bd7f0b5b9e7523975102d81/src/libexpr/lexer.l#L159-L162
To be efficient, we accept any $ followed by something that's not a
opening curly brace ('{') as normal string content. But we cannot accept
"$'", as the last single quote could be part of a double single-quote,
thus ending the multiline-string.
The corner case of a single single-quote following a dollar requires a
lookahead and has been left out (forgotten ? :-)) in the lexer.
For advanced usages of multiline-strings, I refer you to the tests in
nix source code :
https://github.com/NixOS/nix/blob/master/tests/lang/eval-okay-ind-string.nix
-- Layus.
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