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add docs on variable expansion

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Evan Martin 2011-06-25 12:37:39 -07:00
parent 998aaac2ab
commit fd6e3582a3
1 changed files with 34 additions and 2 deletions
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doc/manual.asciidoc
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@ -373,7 +373,6 @@ A file is a series of declarations. A declaration can be one of:
_dependency1_ _dependency2_+. (See <<ref_dependencies,the reference on
dependency types>>.)
3. Variable declarations, which look like +_variable_ = _value_+.
4. References to more files, which look like +subninja _path_+ or
@ -422,7 +421,6 @@ not an error if the listed dependency is missing. This allows you to
delete a depfile-discovered header file and rebuild, without the build
aborting due to a missing input.
`description`:: a short description of the command, used to pretty-print
the command as it's running. The `-v` flag controls whether to print
the full command or its description; if a command fails, the full command
@ -498,6 +496,40 @@ lookup order for a variable referenced in a rule is:
4. Variables from the file that included that file using the
`subninja` keyword.
Variable expansion
~~~~~~~~~~~~~~~~~~
Variables are expanded in two cases: in the right side of a `name =
value` statement and in paths in a `build` statement.
When a `name = value` statement is evaluated, its right-hand side is
expanded once (according to the above scoping rules) immediately, and
from then on `$name` expands to the static string as the result of the
expansion. It is never the case that you'll need to "double-escape" a
variable with some syntax like `$$foo`.
A `build` statement is first parsed as a space-separated list of
filenames and then each name is expanded. This means that spaces
within a variable will result in spaces in the expanded filename.
----
spaced = foo bar
build $spaced/baz other: ...
# The above build line has two outputs: "foo bar/baz" and "other".
----
In a `name = value` statement, whitespace at the beginning of a value
is always stripped. Whitespace at the beginning of a line after a
line continuation is also stripped.
----
two_words_with_one_space = foo $
bar
one_word_with_no_space = foo$
bar
----
Future work
-----------