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Using The Command Line

In Enterprise Linux, the command line is the tool of choice for most tasks. Getting comfortable with it is key — most developers and admins SSH into servers and use the command line for their daily work.

CLI Command Syntax

Most standard commands have three parts (though the last two are often optional):

  1. Command
  2. Option (optional)
  3. Argument (optional)

For example:

ls -ltr /etc/

Which breaks down like this:

  ls    -ltr    /etc/
   ^      ^       ^
COMMAND OPTION ARGUMENT

CLI Commands with Irregular Options

Not every command follows this neat structure. Many advanced commands mix things up a bit:

grep -r 'conf' /etc/ # Recursively search for "conf" in all files in /etc
find /etc -name "*journald**" -exec ls -ltr {} \; # Find files with "journald" in the name and list them
ps aux # List running processes (no hyphen for options here)

Single vs Double Hyphen Options

Some commands accept both single and double hyphens. Single hyphens usually mean each letter is a separate option, while double hyphens spell out full words. For example:

lvcreate -h
lvcreate --help

Both commands will show the help output.

CLI Visual Cues

You can tell if you're running as root or a normal user by looking at the prompt.

A normal user's prompt looks like this (note the $):

[brad@localhost ~]$ <commandGoesHere>

The root user gets a hash (#) at the end:

[root@localhost ~]# <commandGoesHere>