nixpkgs/pkgs/lib/strings.nix

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/* String manipulation functions. */
let lib = import ./default.nix;
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inherit (builtins) add sub lessThan length;
in
rec {
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inherit (builtins) stringLength substring head tail;
# 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);
concatImapStrings = f: list: concatStrings (lib.imap f list);
# Place an element between each element of a list, e.g.,
# `intersperse "," ["a" "b" "c"]' returns ["a" "," "b" "," "c"].
intersperse = separator: list:
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if list == [] || length list == 1
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";
# Idem for Perl search paths.
makePerlPath = makeSearchPath "lib/perl5/site_perl";
# 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 map (p: substring p 1 s) (lib.range 0 (sub l 1));
# Manipulate a string charcater by character and replace them by strings
# before concatenating the results.
stringAsChars = f: s:
concatStrings (
map f (stringToCharacters s)
);
# same as vim escape function.
# Each character contained in list is prefixed by "\"
escape = list : string :
stringAsChars (c: if lib.elem c list then "\\${c}" else c) string;
# still ugly slow. But more correct now
# [] for zsh
escapeShellArg = lib.escape (stringToCharacters "\\ ';$`()|<>\t*[]");
# replace characters by their substitutes. This function is equivalent to
# the `tr' command except that one character can be replace by multiple
# ones. e.g.,
# replaceChars ["<" ">"] ["&lt;" "&gt;"] "<foo>" returns "&lt;foo&gt;".
replaceChars = del: new: s:
let
subst = c:
(lib.fold
(sub: res: if sub.fst == c then sub else res)
{fst = c; snd = c;} (lib.zipLists del new)
).snd;
in
stringAsChars subst 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);
# 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;
# Return true iff string v1 denotes a version older than v2.
versionOlder = v1: v2: builtins.compareVersions v2 v1 == 1;
# Extract name with version from URL. Ask for separator which is
# supposed to start extension
nameFromURL = url: sep: let
components = splitString "/" url;
filename = lib.last components;
name = builtins.head (splitString sep filename);
in
assert ! eqStrings name filename;
name;
}