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| author | Ray Strode <rstrode@redhat.com> | 2016-08-09 10:20:22 -0400 |
|---|---|---|
| committer | Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> | 2017-02-20 23:32:53 -0500 |
| commit | b82f58bfe396b395bce3452bc0ba2f972fb01ab8 (patch) | |
| tree | 02767a48aced8b08db4aba14890a224a97c05111 /man/environment.d.xml | |
| parent | 4bed076c5f79ce26451ea3d73950d895f630f9a7 (diff) | |
| download | systemd-b82f58bfe396b395bce3452bc0ba2f972fb01ab8.tar.gz | |
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/environment.d.xml')
| -rw-r--r-- | man/environment.d.xml | 16 |
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> |