# list

List operations.

## Synopsis

    Reading
      list(LENGTH <list> <out-var>)
      list(GET <list> <element index> [<index> ...] <out-var>)
      list(JOIN <list> <glue> <out-var>)
      list(SUBLIST <list> <begin> <length> <out-var>)

    Search
      list(FIND <list> <value> <out-var>)

    Modification
      list(APPEND <list> [<element>...])
      list(FILTER <list> {INCLUDE | EXCLUDE} REGEX <regex>)
      list(INSERT <list> <index> [<element>...])
      list(POP_BACK <list> [<out-var>...])
      list(POP_FRONT <list> [<out-var>...])
      list(PREPEND <list> [<element>...])
      list(REMOVE_ITEM <list> <value>...)
      list(REMOVE_AT <list> <index>...)
      list(REMOVE_DUPLICATES <list>)
      list(TRANSFORM <list> <ACTION> [...])

    Ordering
      list(REVERSE <list>)
      list(SORT <list> [...])

## Introduction

The list subcommands `APPEND`, `INSERT`, `FILTER`, `PREPEND`, `POP_BACK`, `POP_FRONT`, `REMOVE_AT`, `REMOVE_ITEM`, `REMOVE_DUPLICATES`, `REVERSE` and `SORT` may create new values for the list within the current CMake variable scope. Similar to the `set()` command, the LIST command creates new variable values in the current scope, even if the list itself is actually defined in a parent scope. To propagate the results of these operations upwards, use `set()` with `PARENT_SCOPE`, `set()` with `CACHE INTERNAL`, or some other means of value propagation.

Note

A list in cmake is a `;` separated group of strings. To create a list the set command can be used. For example, `set(var a b c d e)` creates a list with `a;b;c;d;e`, and `set(var "a b c d e")` creates a string or a list with one item in it. (Note macro arguments are not variables, and therefore cannot be used in LIST commands.)

Note

When specifying index values, if `<element index>` is 0 or greater, it is indexed from the beginning of the list, with 0 representing the first list element. If `<element index>` is -1 or lesser, it is indexed from the end of the list, with -1 representing the last list element. Be careful when counting with negative indices: they do not start from 0. -0 is equivalent to 0, the first list element.

## Reading

    list(LENGTH <list> <output variable>)

Returns the list's length.

    list(GET <list> <element index> [<element index> ...] <output variable>)

Returns the list of elements specified by indices from the list.

    list(JOIN <list> <glue> <output variable>)

New in version 3.12.

Returns a string joining all list's elements using the glue string. To join multiple strings, which are not part of a list, use `JOIN` operator from `string()` command.

    list(SUBLIST <list> <begin> <length> <output variable>)

New in version 3.12.

Returns a sublist of the given list. If `<length>` is 0, an empty list will be returned. If `<length>` is -1 or the list is smaller than `<begin>+<length>` then the remaining elements of the list starting at `<begin>` will be returned.

## Search

    list(FIND <list> <value> <output variable>)

Returns the index of the element specified in the list or -1 if it wasn't found.

## Modification

    list(APPEND <list> [<element> ...])

Appends elements to the list. If no variable named `<list>` exists in the current scope its value is treated as empty and the elements are appended to that empty list.

    list(FILTER <list> <INCLUDE|EXCLUDE> REGEX <regular_expression>)

New in version 3.6.

Includes or removes items from the list that match the mode's pattern. In `REGEX` mode, items will be matched against the given regular expression.

For more information on regular expressions look under string(REGEX).

    list(INSERT <list> <element_index> <element> [<element> ...])

Inserts elements to the list to the specified index. It is an error to specify an out-of-range index. Valid indexes are 0 to N where N is the length of the list, inclusive. An empty list has length 0. If no variable named `<list>` exists in the current scope its value is treated as empty and the elements are inserted in that empty list.

    list(POP_BACK <list> [<out-var>...])

New in version 3.15.

If no variable name is given, removes exactly one element. Otherwise, with N variable names provided, assign the last N elements' values to the given variables and then remove the last N values from `<list>`.

    list(POP_FRONT <list> [<out-var>...])

New in version 3.15.

If no variable name is given, removes exactly one element. Otherwise, with N variable names provided, assign the first N elements' values to the given variables and then remove the first N values from `<list>`.

    list(PREPEND <list> [<element> ...])

New in version 3.15.

Insert elements to the 0th position in the list. If no variable named `<list>` exists in the current scope its value is treated as empty and the elements are prepended to that empty list.

    list(REMOVE_ITEM <list> <value> [<value> ...])

Removes all instances of the given items from the list.

    list(REMOVE_AT <list> <index> [<index> ...])

Removes items at given indices from the list.

    list(REMOVE_DUPLICATES <list>)

Removes duplicated items in the list. The relative order of items is preserved, but if duplicates are encountered, only the first instance is preserved.

    list(TRANSFORM <list> <ACTION> [<SELECTOR>]
                          [OUTPUT_VARIABLE <output variable>])

New in version 3.12.

Transforms the list by applying an action to all or, by specifying a `<SELECTOR>`, to the selected elements of the list, storing the result in-place or in the specified output variable.

Note

The `TRANSFORM` sub-command does not change the number of elements in the list. If a `<SELECTOR>` is specified, only some elements will be changed, the other ones will remain the same as before the transformation.

`<ACTION>` specifies the action to apply to the elements of the list. The actions have exactly the same semantics as sub-commands of the `string()` command. `<ACTION>` must be one of the following:

`APPEND`, `PREPEND`: Append, prepend specified value to each element of the list.

>     list(TRANSFORM <list> <APPEND|PREPEND> <value> ...)

`TOUPPER`, `TOLOWER`: Convert each element of the list to upper, lower characters.

>     list(TRANSFORM <list> <TOLOWER|TOUPPER> ...)

`STRIP`: Remove leading and trailing spaces from each element of the list.

>     list(TRANSFORM <list> STRIP ...)

`GENEX_STRIP`: Strip any `generator expressions` from each element of the list.

>     list(TRANSFORM <list> GENEX_STRIP ...)

`REPLACE`: Match the regular expression as many times as possible and substitute the replacement expression for the match for each element of the list (Same semantic as `REGEX REPLACE` from `string()` command).

>     list(TRANSFORM <list> REPLACE <regular_expression>
>                                   <replace_expression> ...)

`<SELECTOR>` determines which elements of the list will be transformed. Only one type of selector can be specified at a time. When given, `<SELECTOR>` must be one of the following:

`AT`: Specify a list of indexes.

>     list(TRANSFORM <list> <ACTION> AT <index> [<index> ...] ...)

`FOR`: Specify a range with, optionally, an increment used to iterate over the range.

>     list(TRANSFORM <list> <ACTION> FOR <start> <stop> [<step>] ...)

`REGEX`: Specify a regular expression. Only elements matching the regular expression will be transformed.

>     list(TRANSFORM <list> <ACTION> REGEX <regular_expression> ...)

## Ordering

    list(REVERSE <list>)

Reverses the contents of the list in-place.

    list(SORT <list> [COMPARE <compare>] [CASE <case>] [ORDER <order>])

Sorts the list in-place alphabetically.

New in version 3.13: Added the `COMPARE`, `CASE`, and `ORDER` options.

New in version 3.18: Added the `COMPARE NATURAL` option.

Use the `COMPARE` keyword to select the comparison method for sorting. The `<compare>` option should be one of:

- `STRING`: Sorts a list of strings alphabetically. This is the default behavior if the `COMPARE` option is not given.

- `FILE_BASENAME`: Sorts a list of pathnames of files by their basenames.

- `NATURAL`: Sorts a list of strings using natural order (see `strverscmp(3)` manual), i.e. such that contiguous digits are compared as whole numbers. For example: the following list 10.0 1.1 2.1 8.0 2.0 3.1 will be sorted as 1.1 2.0 2.1 3.1 8.0 10.0 if the `NATURAL` comparison is selected where it will be sorted as 1.1 10.0 2.0 2.1 3.1 8.0 with the `STRING` comparison.

Use the `CASE` keyword to select a case sensitive or case insensitive sort mode. The `<case>` option should be one of:

- `SENSITIVE`: List items are sorted in a case-sensitive manner. This is the default behavior if the `CASE` option is not given.

- `INSENSITIVE`: List items are sorted case insensitively. The order of items which differ only by upper/lowercase is not specified.

To control the sort order, the `ORDER` keyword can be given. The `<order>` option should be one of:

- `ASCENDING`: Sorts the list in ascending order. This is the default behavior when the `ORDER` option is not given.

- `DESCENDING`: Sorts the list in descending order.