nixpkgs/pkgs/lib/strings.nix

124 lines
4 KiB
Nix
Raw Normal View History

/* String manipulation functions. */
let lib = import ./default.nix;
inherit (builtins) add sub lessThan;
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);
# same as vim escape function.
# Each character contained in list is prefixed by "\"
escape = list : string :
lib.concatStrings (map (c: if lib.elem c list then "\\${c}" else c) (stringToCharacters string));
# still ugly slow. But more correct now
# [] for zsh
escapeShellArg = lib.escape (stringToCharacters "\\ ';$`()|<>\t*[]");
# 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);
# Cut a string with a separator and produces a list of strings which were
# separated by this separator. e.g.,
# `splitString "." "foo.bar.baz"' returns ["foo" "bar" "baz"].
splitString = sep: s:
let
sepLen = stringLength sep;
sLen = stringLength s;
lastSearch = sub sLen sepLen;
startWithSep = startAt:
substring startAt sepLen s == sep;
recurse = index: startAt:
let cutUntil = i: [(substring startAt (sub i startAt) s)]; in
if lessThan index lastSearch then
if startWithSep index then
let restartAt = add index sepLen; in
cutUntil index ++ recurse restartAt restartAt
else
recurse (add index 1) startAt
else
cutUntil sLen;
in
recurse 0 0;
# return the suffix of the second argument if the first argument match its
# prefix. e.g.,
# `removePrefix "foo." "foo.bar.baz"' returns "bar.baz".
removePrefix = pre: s:
let
preLen = stringLength pre;
sLen = stringLength s;
in
if pre == substring 0 preLen s then
substring preLen (sub sLen preLen) s
else
s;
}