The JAR command is include in some, but not all installations of Java. On a Linux system, the which command can be used to determine if the JAR command is part of your $PATH. If something like this is returned, you may need to install Java on your Linux system.
~]# which jar /usr/bin/which: no jar in (/sbin:/bin:/usr/sbin:/usr/bin)
The jar command can be used to create a jar (java archive) file. Let's take an example where the /var/www/html directory contains some HTML, CSS, and JS files. The following command will create a war file named MyWebArchive.jar that contains all of the files at and below /var/www/html.
[john.doe@server1 ~]# jar -cvf example.jar /var/www/html added manifest adding: var/www/html/index.html(in = 0) (out = 0) (stored 0%) adding: var/www/html/about.html(in = 0) (out = 0) (stored 0%)