The "who" command.
Ironically, the command to see who is logged into the system is who. You can also see who is logged on using the wcommand.
The ls command.
See related link.
Use the 'ls' command.Try 'man ls' to see the options
The 'ps' command may differ slightly in different versions of unix operating systems. It is usually better to use the 'man ps' command or the 'info ps' command to see the options that are available for your distribution.
Use the 'ps' command. This command lists all of the processes running on the system, when they started, who the owner is, etc.
Several different versions of UNIX have GUI's or Graphical User Interfaces. The most common example of UNIX with an interface is Mac OS X.
To complex to answer completely here - see related link.
The 'merge' command is not standard in Unix, so not every system has it. The 'cat' command is standard in every Unix system. The 'cat' command merely echoes the contents of a file. It can be used to put together several files (concatenate). The 'merge' command (at least on Linux) merges changes from an original file to a modified (patched) file. It is considered a 3-way merge utility. Check the 'man' command for both and you will see the differences in the two commands.
The basic 'who' command lets you see the time of last system boot; list of users logged-in; the current run level, etc.
At the prompt, type:whoThe output will be similar to:Alice tty1 2010-05-21 15:13 (:0)bob pts/0 2010-05-21 15:57 (:0.0)To see more options of the 'who' command, run 'man who' at the prompt.
If you try the command 'man sed' you see it is listed as one of the examples of what sed can do.