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| author |   Tim Yamin <plasmaroo@gentoo.org> | 2006-02-22 04:01:23 +0000 |
|---|---|---|
| committer | Tim Yamin <plasmaroo@gentoo.org> | 2006-02-22 04:01:23 +0000 |
| commit | 07a0d2875d93c658d14a0ce87ce95b4150977596 (patch) | |
| tree | 8dfa36a3e97fabcf0ac9ec3313d03c06ec45e361 /ebuild-writing/use-conditional-code | |
| parent | More updates. Update the stylesheet adding a few new elements and more sh (diff) | |
| download | devmanual-07a0d2875d93c658d14a0ce87ce95b4150977596.tar.gz devmanual-07a0d2875d93c658d14a0ce87ce95b4150977596.tar.bz2 devmanual-07a0d2875d93c658d14a0ce87ce95b4150977596.zip | |
More goodies; change syntax highlighting mode within quotes for ebuilds.
git-svn-id: svn+ssh://svn.gentoo.org/var/svnroot/devmanual/trunk@5 176d3534-300d-0410-8db8-84e73ed771c3
Diffstat (limited to 'ebuild-writing/use-conditional-code')
| -rw-r--r-- | ebuild-writing/use-conditional-code/text.xml | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/ebuild-writing/use-conditional-code/text.xml b/ebuild-writing/use-conditional-code/text.xml new file mode 100644 index 0000000..84fc490 --- /dev/null +++ b/ebuild-writing/use-conditional-code/text.xml @@ -0,0 +1,62 @@ +<?xml version="1.0"?> +<guide self="ebuild-writing/use-conditional-code/"> +<chapter> +<title>USE Flag Conditional Code</title> + +<body> +<p> +Often a particular block of code must only be executed if a given USE flag is +set (or unset). For large blocks, <c>if use foo</c> is best, or for inverse tests +either <c>if ! use foo</c> or <c>if use !foo</c> can be used (the former is more +common and is recommended for readability). For single-statement conditions, the +<c>use foo && blah</c> (or <c>use foo || blah</c> for negatives) form is often more +readable. +</p> + +<p> +The <c>if [ "`use foo`" ]</c> and <c>if [ -n "`use foo`" ]</c> forms which are +occasionally seen in older code must <b>not</b> be used. +</p> + +<note> +<c>die</c> will not work as expected within a subshell, so code in the +form <c>use foo && ( blah ; blah )</c> should be avoided in favour of a proper if +statement. See `die and Subshells`_. +</note> + +<codesample lang="ebuild"> + # USE conditional blocks... + if use livecd ; then + # remove some extra files for a small livecd install + rm -fr ${vimfiles}/{compiler,doc,ftplugin,indent} + fi + + # Inverse USE conditional blocks... + if ! use cscope ; then + # the --disable-cscope configure arg doesn't quite work properly, + # so sed it out of feature.h if we're not USEing cscope. + sed -i -e '/# define FEAT_CSCOPE/d' src/feature.h || die "couldn't disable cscope" + fi + + # USE conditional statements... + use ssl && epatch ${FILESDIR}/${P}-ssl.patch + use sparc && filter-flags -fomit-frame-pointer + + # Inverse USE conditional statements... + use ncurses || epatch ${FILESDIR}/${P}-no-ncurses.patch +</codesample> + +<p> +For echoing content based upon a USE flag, there is often a better helper +function available. +</p> + +<p> +You must not rely upon <c>use</c> producing an output -- this no longer happens. +If you really need output displayed, use the <c>usev</c> function. The +<c>useq</c> function is available for explicitly requesting no output. +</p> +</body> + +</chapter> +</guide> |