# 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.

    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 location.

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

New in version 3.15.

If no variable name is given, removes exactly one element. Otherwise, assign the last element's value to the given variable and removes it, up to the last variable name given.

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

New in version 3.15.

If no variable name is given, removes exactly one element. Otherwise, assign the first element's value to the given variable and removes it, up to the last variable name given.

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

New in version 3.15.

Insert elements to the 0th position in the 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.