Can jconsole data be retrieved from the command line?

You can use this jmx query tool by command line: http://crawler.archive.org/cmdline-jmxclient/

jconsole just provides a wrapper around the JMX MBeans that are in the platform MBeanServer.

You can write a program to connect to your VM using the Attach API which would then query the MBeans.

Or you can expose the platform MBeanServer over RMI and query the MBeans that way.

See the java.lang.management package for more info

Maybe jvmtop is worth a look.
It's a command-line tool which provides a live-view for several metrics.

Example output of the VM overview mode:

 JvmTop 0.4.1  amd64  8 cpus, Linux 2.6.32-27, load avg 0.12
 http://code.google.com/p/jvmtop

  PID MAIN-CLASS      HPCUR HPMAX NHCUR NHMAX    CPU     GC    VM USERNAME   #T DL
 3370 rapperSimpleApp  165m  455m  109m  176m  0.12%  0.00% S6U37 web        21
11272 ver.resin.Resin [ERROR: Could not attach to VM]
27338 WatchdogManager   11m   28m   23m  130m  0.00%  0.00% S6U37 web        31
19187 m.jvmtop.JvmTop   20m 3544m   13m  130m  0.93%  0.47% S6U37 web        20
16733 artup.Bootstrap  159m  455m  166m  304m  0.12%  0.00% S6U37 web        46