Overview of the Nix Language: Difference between revisions
imported>Roberth |
imported>Mickours →Convert a string to an (import-able) path: Add String + path insights |
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This trick might be helpful in combination with [https://nixos.org/nix/manual/#builtin-getEnv <code>builtins.getEnv</code>], which returns a string (which might be a path). Be careful, depending on environment variables introduces heavy non-determinism and might lead to rebuilds! | This trick might be helpful in combination with [https://nixos.org/nix/manual/#builtin-getEnv <code>builtins.getEnv</code>], which returns a string (which might be a path). Be careful, depending on environment variables introduces heavy non-determinism and might lead to rebuilds! | ||
If you need to '''build a path from a mix of paths and strings variables''', you can concatenate strings and paths, but you need to be careful of the evaluation order because Nix removes trailing <code>/</code>. | |||
For example if you need to concatenate <code>/data</code> with a variable call <code>my_var</code> you need to add parenthesis: | |||
<syntaxHighlight lang=nix> | |||
nix-repl> let my_var = "tmp"; in /data + "/" + my_var # WRONG | |||
/datatmp | |||
nix-repl> let my_var = "tmp"; in /data + ("/" + my_var) # Better :) | |||
/data/tmp | |||
</syntaxHighlight> | |||
=== Writing update scripts / Referencing a relative path as string === | === Writing update scripts / Referencing a relative path as string === | ||