adding classpath in linux

Question

export CLASSPATH=.;../somejar.jar;../mysql-connector-java-5.1.6-bin.jar
java -Xmx500m folder.subfolder../dit1/some.xml
cd ..

is the above statement for setting the classpath to already existing classpath in linux is correct or not

Answer 1

I don't like setting CLASSPATH. CLASSPATH is a global variable and as such it is evil:

• If you modify it in one script, suddenly some java programs will stop working.
• If you put there the libraries for all the things which you run, and it gets cluttered.
• You get conflicts if two different applications use different versions of the same library.
• There is no performance gain as libraries in the CLASSPATH are not shared - just their name is shared.
• If you put the dot (.) or any other relative path in the CLASSPATH that means a different thing in each place - that will cause confusion, for sure.

Therefore the preferred way is to set the classpath per each run of the jvm, for example:

java -Xmx500m -cp ".:../somejar.jar:../mysql-connector-java-5.1.6-bin.jar"    "folder.subfolder../dit1/some.xml

If it gets long the standard procedure is to wrap it in a bash or batch script to save typing.

Answer 2

It's always advised to never destructively destroy an existing classpath unless you have a good reason.

The following line preserves the existing classpath and adds onto it.

export CLASSPATH="$CLASSPATH:foo.jar:../bar.jar"

Answer 3

Important difference between setting Classpath in Windows and Linux is path separator which is ";" (semi-colon) in Windows and ":" (colon) in Linux. Also %PATH% is used to represent value of existing path variable in Windows while ${PATH} is used for same purpose in Linux (in the bash shell). Here is the way to setup classpath in Linux:

export CLASSPATH=${CLASSPATH}:/new/path

but as such Classpath is very tricky and you may wonder why your program is not working even after setting correct Classpath. Things to note:

1. -cp options overrides CLASSPATH environment variable.
2. Classpath defined in Manifest file overrides both -cp and CLASSPATH envorinment variable.

Reference: How Classpath works in Java.

Answer 4

Paths under linux are separated by colons (:), not semi-colons (;), as theatrus correctly used it in his example. I believe Java respects this convention.

Edit

Alternatively to what andy suggested, you may use the following form (which sets CLASSPATH for the duration of the command):

CLASSPATH=".:../somejar.jar:../mysql-connector-java-5.1.6-bin.jar" java -Xmx500m ...

whichever is more convenient to you.