Shell basics and getting help

What is the shell?

A terminal is the window where you type. The shell is the program inside it that reads your line, works out what you mean and runs it. RHEL uses bash (the Bourne Again SHell) by default. The prompt tells you who and where you are:

[asha@web01 ~]$     <- user asha, host web01, in the home directory (~), $ = normal user
[root@web01 log]#    <- user root, in a directory named log, # = root (admin)

The shape of a command

Most commands follow one pattern: command, then options, then arguments. An option changes how the command behaves. Short options are one dash and one letter (-l), and you can combine them (-la). Long options use two dashes and a word (--all). An argument is what the command works on, usually a file or directory.

$ ls -l --human-readable /var/log/messages
-rw-------. 1 root root 1.2M Oct 19 10:15 /var/log/messages

Keys that save hours

• Tab: completes command and file names. Press it twice to see all choices. It also stops typing mistakes.
• Up arrow: brings back earlier commands. history lists them; !42 runs number 42 again.
• Ctrl+R: search back through your history. Type part of an old command.
• Ctrl+C: stop the running command. Ctrl+L or clear: clean the screen.
• Ctrl+A / Ctrl+E: jump to the start / end of the line.

Getting help without Google

In an exam like RHCSA, and on many secure company servers, you have no internet. The help is already on the machine.

$ ls --help | head -3
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

$ man ls          # full manual page; q quits, /word searches, n = next match
$ man 5 passwd    # section 5: the FORMAT of the /etc/passwd file
$ man -k partition
fdisk (8)            - manipulate disk partition table
parted (8)           - a partition manipulation program
...

Man pages are grouped in numbered sections. The ones you need most: 1 = user commands, 5 = file formats, 8 = admin commands. passwd(1) is the command; passwd(5) explains the file. If man -k finds nothing, the search index may be old; root can rebuild it with mandb.

Many packages also install examples and notes in /usr/share/doc. When you forget the exact syntax of a config file, look there and at the EXAMPLES part near the end of the man page.

Who am I, where am I?

$ whoami
asha
$ id
uid=1000(asha) gid=1000(asha) groups=1000(asha),10(wheel)
$ hostname
web01.example.com
$ date
Mon Oct 19 10:20:31 IST 2026

Common mistakes

• Forgetting the space: ls-l is not ls -l. The shell looks for a command named "ls-l".
• Wrong case: LS and ls are different. Linux is case-sensitive everywhere.
• Pasting commands from a website without reading them, especially ones with sudo or rm. Read every line first.
• Working as root all day. Use a normal user and sudo only when needed.