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authorRay Strode <rstrode@redhat.com>2016-08-09 10:20:22 -0400
committerZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2017-02-20 23:32:53 -0500
commitb82f58bfe396b395bce3452bc0ba2f972fb01ab8 (patch)
tree02767a48aced8b08db4aba14890a224a97c05111 /man
parent4bed076c5f79ce26451ea3d73950d895f630f9a7 (diff)
basic: support default and alternate values for env expansion
Sometimes it's useful to provide a default value during an environment expansion, if the environment variable isn't already set. For instance $XDG_DATA_DIRS is suppose to default to: /usr/local/share/:/usr/share/ if it's not yet set. That means callers wishing to augment XDG_DATA_DIRS need to manually add those two values. This commit changes replace_env to support the following shell compatible default value syntax: XDG_DATA_DIRS=/foo:${XDG_DATA_DIRS:-/usr/local/share/:/usr/share} Likewise, it's useful to provide an alternate value during an environment expansion, if the environment variable isn't already set. For instance, $LD_LIBRARY_PATH will inadvertently search the current working directory if it starts or ends with a colon, so the following is usually wrong: LD_LIBRARY_PATH=/foo/lib:${LD_LIBRARY_PATH} To address that, this changes replace_env to support the following shell compatible alternate value syntax: LD_LIBRARY_PATH=/foo/lib${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}} [zj: gate the new syntax under REPLACE_ENV_ALLOW_EXTENDED switch, so existing callers are not modified.]
Diffstat (limited to 'man')
-rw-r--r--man/environment.d.xml16
1 files changed, 12 insertions, 4 deletions
diff --git a/man/environment.d.xml b/man/environment.d.xml
index 4022c25c36..be7758a2f9 100644
--- a/man/environment.d.xml
+++ b/man/environment.d.xml
@@ -78,8 +78,16 @@
<literal><replaceable>KEY</replaceable>=<replaceable>VALUE</replaceable></literal> environment
variable assignments, separated by newlines. The right hand side of these assignments may
reference previously defined environment variables, using the <literal>${OTHER_KEY}</literal>
- and <literal>$OTHER_KEY</literal> format. No other elements of shell syntax are supported.
- </para>
+ and <literal>$OTHER_KEY</literal> format. It is also possible to use
+
+ <literal>${<replaceable>FOO</replaceable>:-<replaceable>DEFAULT_VALUE</replaceable>}</literal>
+ to expand in the same way as <literal>${<replaceable>FOO</replaceable>}</literal> unless the
+ expansion would be empty, in which case it expands to <replaceable>DEFAULT_VALUE</replaceable>,
+ and use
+ <literal>${<replaceable>FOO</replaceable>:+<replaceable>ALTERNATE_VALUE</replaceable>}</literal>
+ to expand to <replaceable>ALTERNATE_VALUE</replaceable> as long as
+ <literal>${<replaceable>FOO</replaceable>}</literal> would have expanded to a non-empty value.
+ No other elements of shell syntax are supported.</para>
<para>Each<replaceable>KEY</replaceable> must be a valid variable name. Empty lines
and lines beginning with the comment character <literal>#</literal> are ignored.</para>
@@ -95,8 +103,8 @@
<programlisting>
FOO_DEBUG=force-software-gl,log-verbose
PATH=/opt/foo/bin:$PATH
- LD_LIBRARY_PATH=/opt/foo/lib
- XDG_DATA_DIRS=/opt/foo/share:${XDG_DATA_DIRS}
+ LD_LIBRARY_PATH=${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}/opt/foo/lib
+ XDG_DATA_DIRS=/opt/foo/share:${XDG_DATA_DIRS:-/usr/local/share/:/usr/share/}
</programlisting>
</example>
</refsect2>