How to chop down a path in a BASH script?

Question

Short version: I want to take the last two components off the results of readlink -f and store it in a variable using a single line of BASH script.

Long version: I would like a single line of BASH script to set the JAVA_HOME variable for the EC2 command-line tools. This variable stores the location of Java's home directory. Using the following I can get the absolute path to the java binary:

$ readlink -f $(which java)

On my test machine, this outputs:

/usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java

That's perfect except I need to chop off "/bin/java". I could use string replace to do this in my profile like so:

JAVA_HOME=$(readlink -f $(which java))
export JAVA_HOME="${JAVA_HOME%/*/*}"

EDITED: Now the only issue with this is that it's two lines. I've accepted an answer below that makes it one, but it still only works on Linux whereas on OS X one must run ./Commands/java_home from this to get the real directory.

Extra credit: make it work on OS X (where readlink -f does not work).

blueblob · Accepted Answer · 2013-11-07T21:40:27.943

5

dirname $(dirname $(readlink -f $(which java)))

edited Nov 07 '13 at 21:40

answered Nov 07 '13 at 21:21

blueblob

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Ah, I think I got it but I changed this to: `dirname $(dirname $(readlink -f $(which java)))`. Is that what you meant to write? – Neil C. Obremski Nov 07 '13 at 21:38

Dan · Answer 2 · 2013-11-08T11:18:15.447

1

For the Mac OS X version, try this:

dirname $(dirname $(perl -e "use Cwd; print Cwd::abs_path('$(which java)')"))

edited Nov 08 '13 at 11:18

answered Nov 07 '13 at 21:31

Dan

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I just ran this on Lion and the output is just `/usr` so I think the Perl is not following symlinks. – Neil C. Obremski Nov 07 '13 at 21:40
Sorry @NeilC.Obremski I screwed up the escaping. Fixed now. – Dan Nov 08 '13 at 11:19
Thanks @Dan, that *works* but there's something else screwy on OS X w/ Java: it points to a folder that has no `./bin`. Instead there's a `./Commands/java_home` command that has to be run to output the real directory ... what a pain! It appears that I can't make a line of BASH script that works between Linux and OS X. – Neil C. Obremski Nov 08 '13 at 18:25

score 0 · Answer 3 · answered Nov 07 '13 at 21:31

0

This should work for extracting /bin/java, even on MAC OSX (untested)

echo ${JAVA_HOME##${JAVA_HOME%/*/*}}

answered Nov 07 '13 at 21:31

epsilon

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Thanks @jbh; I'll update my description because this *does* work for the string replace, but what I was looking for was a full command based on `which java`. – Neil C. Obremski Nov 08 '13 at 18:26
Also, I think you just meant `echo ${JAVA_HOME%/*/*}` (otherwise it outputs `/Commands/java`) – Neil C. Obremski Nov 08 '13 at 18:35

How to chop down a path in a BASH script?

3 Answers3