Github user nchammas commented on a diff in the pull request:
https://github.com/apache/spark/pull/4224#discussion_r23698613
--- Diff: ec2/spark-ec2 ---
@@ -20,6 +20,6 @@
# Preserve the user's CWD so that relative paths are passed correctly to
#+ the underlying Python script.
-SPARK_EC2_DIR="$(dirname $0)"
+SPARK_EC2_DIR="$(dirname "$0")"
--- End diff --
`$()` invokes a subshell, so the quotes inside the subshell are processed
independently of those outside.
So here we're making sure `dirname` gets exactly 1 argument by quoting the
`$0`, in case the value of `$0` has spaces.
Then, we're making sure the output of `dirname` in turn is captured as 1
argument when passed to `SPARK_EC2_DIR` by quoting the whole subshell, in case
that output has spaces.
Welcome to the most deceptive feature of Bash: [Word
Splitting](http://mywiki.wooledge.org/WordSplitting).
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