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Concatenate list of paths in bash-script, with colon as separator

I have the following difficult to read script consisting of a single command:

#!/bin/sh

/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/bin/java 
-classpath /Users/afarber/src/jetty-newbie/EmbeddedWebsocket/target/classes:/Users/afarber/.m2/repository/org/eclipse/jetty/jetty-server/9.3.9.v20160517/jetty-server-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/javax/servlet/javax.servlet-api/3.1.0/javax.servlet-api-3.1.0.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/jetty-http/9.3.9.v20160517/jetty-http-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/jetty-util/9.3.9.v20160517/jetty-util-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/jetty-io/9.3.9.v20160517/jetty-io-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/jetty-servlet/9.3.9.v20160517/jetty-servlet-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/jetty-security/9.3.9.v20160517/jetty-security-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-api/9.3.9.v20160517/websocket-api-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-server/9.3.9.v20160517/websocket-server-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-common/9.3.9.v20160517/websocket-common-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-client/9.3.9.v20160517/websocket-client-9.3.9.v20160517.jar:/Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-servlet/9.3.9.v20160517/websocket-servlet-9.3.9.v20160517.jar 
de.afarber.MyServlet

As slight readability improvement I would like to list all the paths after the -classpath in a separate variable, each aligned after the other:

PATHS=  /Users/afarber/src/jetty-newbie/EmbeddedWebsocket/target/classes 
        /Users/afarber/.m2/repository/org/eclipse/jetty/jetty-server/9.3.9.v20160517/jetty-server-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/javax/servlet/javax.servlet-api/3.1.0/javax.servlet-api-3.1.0.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/jetty-http/9.3.9.v20160517/jetty-http-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/jetty-util/9.3.9.v20160517/jetty-util-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/jetty-io/9.3.9.v20160517/jetty-io-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/jetty-servlet/9.3.9.v20160517/jetty-servlet-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/jetty-security/9.3.9.v20160517/jetty-security-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-api/9.3.9.v20160517/websocket-api-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-server/9.3.9.v20160517/websocket-server-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-common/9.3.9.v20160517/websocket-common-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-client/9.3.9.v20160517/websocket-client-9.3.9.v20160517.jar 
        /Users/afarber/.m2/repository/org/eclipse/jetty/websocket/websocket-servlet/9.3.9.v20160517/websocket-servlet-9.3.9.v20160517.jar 

This way I can easier add and remove the paths, and sort them in Vim.

My question is: how to join them back for my command?

UPDATE:

If all JAR-files would be located in the same dir, I could have used the new Java 8 wildcard syntax java -classpath "/that/dir/*" de.afarber.MyServlet – but that wasn’t the case here.

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Answer

Since you are using bash, you can store the directory names in an array (with some refactoring just to make this example more readable):

repo=/Users/afarber/.m2/repository
jetty="$repo/org/eclipse/jetty"
websocket="$jetty/websocket"
paths=(
    /Users/afarber/src/jetty-newbie/EmbeddedWebsocket/target/classes
    "$jetty"/jetty-server/9.3.9.v20160517/jetty-server-9.3.9.v20160517.jar
    $repo/javax/servlet/javax.servlet-api/3.1.0/javax.servlet-api-3.1.0.jar
    "$jetty"/jetty-http/9.3.9.v20160517/jetty-http-9.3.9.v20160517.jar
    "$jetty"/jetty-util/9.3.9.v20160517/jetty-util-9.3.9.v20160517.jar
    "$jetty"/jetty-io/9.3.9.v20160517/jetty-io-9.3.9.v20160517.jar
    "$jetty"/jetty-servlet/9.3.9.v20160517/jetty-servlet-9.3.9.v20160517.jar
    "$jetty"/jetty-security/9.3.9.v20160517/jetty-security-9.3.9.v20160517.jar
    "$websocket"/websocket-api/9.3.9.v20160517/websocket-api-9.3.9.v20160517.jar
    "$websocket"/websocket-server/9.3.9.v20160517/websocket-server-9.3.9.v20160517.jar
    "$websocket"/websocket-common/9.3.9.v20160517/websocket-common-9.3.9.v20160517.jar
    "$websocket"/websocket-client/9.3.9.v20160517/websocket-client-9.3.9.v20160517.jar
    "$websocket"/websocket-servlet/9.3.9.v20160517/websocket-servlet-9.3.9.v20160517.jar 
)

Note you don’t need to end each line with a backslash; whitespace (including newlines) separate elements of the array. Once you have the array, you can join the elements with a colon using parameter expansion with a modified value of the IFS parameter.

/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/bin/java 
  -classpath "$(IFS=:; echo "${paths[*]}")" de.afarber.MyServlet
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