From 21d3a5af7d2e1884009cfd1ad650a937438f5991 Mon Sep 17 00:00:00 2001
From: Vlastimil Holer <vlastimil.holer@gmail.com>
Date: Thu, 20 Dec 2012 13:57:57 +0100
Subject: Add explanation on how context variables parsing works.
---
cloudinit/sources/DataSourceOpenNebula.py | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
(limited to 'cloudinit/sources')
diff --git a/cloudinit/sources/DataSourceOpenNebula.py b/cloudinit/sources/DataSourceOpenNebula.py
index 1622a66e..a50b0c10 100644
--- a/cloudinit/sources/DataSourceOpenNebula.py
+++ b/cloudinit/sources/DataSourceOpenNebula.py
@@ -167,10 +167,24 @@ def read_context_disk_dir(source_dir):
}
if "context.sh" in found:
- # let bash process the contextualization script;
- # write out data in normalized output NAME=\$?'?VALUE'?
- # TODO: don't trust context.sh! parse manually !!!
try:
+ # Note: context.sh is a "shell" script with defined context
+ # variables, like: X="Y" . It's ready to use as a shell source
+ # e.g.: ". context.sh" and as a shell script it can also reference
+ # to already defined shell variables. So to have same context var.
+ # values as we can have in custom shell script, we use bash itself
+ # to read context.sh and dump variables in easily parsable way.
+ #
+ # normalized variables dump format (get by cmd "set"):
+ # 1. simple single word assignment ........ X=Y
+ # 2. multiword assignment ................. X='Y Z'
+ # 3. assignments with backslash escapes ... X=$'Y\nZ'
+ #
+ # how context variables are read:
+ # 1. list existing ("old") shell variables and store into $VARS
+ # 2. read context variables
+ # 3. use comm to filter "old" variables from all current
+ # variables and excl. few other vars with grep
BASH_CMD='VARS=`set | sort -u `;' \
'. %s/context.sh;' \
'comm -23 <(set | sort -u) <(echo "$VARS") | egrep -v "^(VARS|PIPESTATUS|_)="'
--
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