nixpkgs/pkgs/lib/strings.nix

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/* String manipulation functions. */
let lib = import ./default.nix; in
rec {
inherit (builtins) stringLength substring head tail lessThan sub;
# Concatenate a list of strings.
concatStrings = lib.fold (x: y: x + y) "";
# Map a function over a list and concatenate the resulting strings.
concatMapStrings = f: list: concatStrings (map f list);
# Place an element between each element of a list, e.g.,
# `intersperse "," ["a" "b" "c"]' returns ["a" "," "b" "," "c"].
intersperse = separator: list:
if list == [] || tail list == []
then list
else [(head list) separator]
++ (intersperse separator (tail list));
# Concatenate a list of strings with a separator between each element, e.g.
# concatStringsSep " " ["foo" "bar" "xyzzy"] == "foo bar xyzzy"
concatStringsSep = separator: list:
concatStrings (intersperse separator list);
# Construct a Unix-style search path consisting of each `subDir"
# directory of the given list of packages. For example,
# `makeSearchPath "bin" ["x" "y" "z"]' returns "x/bin:y/bin:z/bin".
makeSearchPath = subDir: packages:
concatStringsSep ":" (map (path: path + "/" + subDir) packages);
# Construct a library search path (such as RPATH) containing the
# libraries for a set of packages, e.g. "${pkg1}/lib:${pkg2}/lib:...".
makeLibraryPath = makeSearchPath "lib";
# Dependening on the boolean `cond', return either the given string
# or the empty string.
optionalString = cond: string: if cond then string else "";
# Determine whether a filename ends in the given suffix.
hasSuffix = ext: fileName:
let lenFileName = stringLength fileName;
lenExt = stringLength ext;
in !(lessThan lenFileName lenExt) &&
substring (sub lenFileName lenExt) lenFileName fileName == ext;
# Convert a string to a list of characters (i.e. singleton strings).
# For instance, "abc" becomes ["a" "b" "c"]. This allows you to,
# e.g., map a function over each character. However, note that this
# will likely be horribly inefficient; Nix is not a general purpose
# programming language. Complex string manipulations should, if
# appropriate, be done in a derivation.
stringToCharacters = s: let l = stringLength s; in
if l == 0
then []
else [(substring 0 1 s)] ++ stringToCharacters (substring 1 (builtins.sub l 1) s);
# !!! this function seems broken - it doesn't escape all special
# characters, and in any case this should be done in a builder.
escapeShellArg = s:
let escapeChar = x: if x == "'" then "'\"'\"'" else x;
in "'" + concatStrings (map escapeChar (stringToCharacters s)) + "'";
# !!! what is this for?
defineShList = name: list: "\n${name}=(${concatStringsSep " " (map escapeShellArg list)})\n";
# arg: http://foo/bar/bz.ext returns bz.ext
# !!! isn't this what the `baseNameOf' primop does?
dropPath = s :
if s == "" then "" else
let takeTillSlash = left : c : s :
if left == 0 then s
else if (__substring left 1 s == "/") then
(__substring (__add left 1) (__sub c 1) s)
else takeTillSlash (__sub left 1) (__add c 1) s; in
takeTillSlash (__sub (__stringLength s) 1) 1 s;
# Compares strings not requiring context equality
# Obviously, a workaround but works on all Nix versions
eqStrings = a: b: (a+(substring 0 0 b)) == ((substring 0 0 a)+b);
}