A handy thing to know for both real-life and any certification exams that you may take, is the structure of a command. Commands can consist of up to three parts, and there’s a certain order for the parts. Here are the parts and the order in which you’ll normally place them:

• The command itself
• Command options
• Command arguments

If you plan to take a Linux certification exam, you’ll definitely want to remember this ordering rule. Later on though, we’ll see that some commands don’t always follow this rule.

Using Command Options

There are two general types of option switches:

• Single-letter options: For most commands, a single-letter option is preceded by a single dash. Most of the time, two or more single-letter options can be combined with a single dash.
• Whole-word options: For most commands, a whole word option is preceded by two dashes. Two or more whole...

From either the command-line or from within shell scripts, it’s handy to know how to combine multiple commands into one single command. In this section, I’ll demonstrate three ways to do that which are:

• Running commands interactively
• Using command sequences
• Using the find utility

Running Commands Interactively

This is a form of shell-script programming, except that you’re just executing all commands from the command-line, instead of actually writing, saving, and executing a script. Here, you are creating a for loop – with each command of the loop on its own separate line – to perform a directory listing three times.

[donnie@fedora ~]$ for var in arg1 arg2 arg3
> do
> echo $var
> ls
> done
. . .
. . .
[donnie@fedora ~]$

At the end of each line, you’ll hit the Enter key. But, nothing will happen until you type the done command on the final line. The...

We’ve already shown you that the find utility is inherently recursive. That is, it will automatically search through the subdirectories of your specified search path without you having to tell it to. Most Linux commands aren’t that way, however. If you want them to work recursively, you’ll have to tell them to. For the most part, this is done with either the -R switch or the -r switch. (Some commands use –R, and some use –r. Something that you’ll eventually see for yourself is that there’s not a lot of consistency in how the different commands work with option switches.) Let’s see how it all works with a hands-on lab.

Hands-on Lab – Using Commands with...

Whenever you work with the command-line, there will be times when you’ll have to enter some commands more than once. If you’ve just entered a command that’s long and complex, you may not exactly be thrilled at the prospect of having to type it in all over again. Not to worry, though. For this, bash and zsh give you the ability to recall and/or edit commands that you’ve previously entered. There are a few ways to do this.

Whenever you enter a command, it gets stored in memory until you exit the shell session. The command will then get added to a file that’s specified by the HISTFILE variable. Usually, this is the .bash_history file on bash, and the .histfile file on zsh. You’ll find these stored in each user’s home directory. To verify that, you can use the echo command, like this:

[donnie@fedora ~]$ echo $HISTFILE
/home/donnie/.bash_history
[donnie@fedora ~]$

On zsh, you’ll see this...

Whenever you type anything on the command-line or into a shell script, you’ll be using a mix of normal alphanumeric text and non-alphanumeric characters. Some of these characters have special meanings within the shell, and will cause the shell to perform in some special way. Sometimes, you’ll want the shell to interpret these special characters as normal text, instead of as something with a magical power. To do that, you can either escape or quote the special characters.

There are two general classes of characters that can be interpreted by the shell from within a shell command. These are:

• Normal characters: bash and zsh interpret these characters literally. In other words, they have no special meaning to the shell.
• Metacharacters: These characters have special meanings for bash and zsh. You could say that a metacharacter provides some sort of special instruction to these shells.

We’ve covered some important basics in this chapter. We started by describing the structure and the components of a shell command, and how to perform multiple actions with just one single command. Then, we looked at the find utility, and the cool things that you can do with it. We then looked at how to run commands recursively, and wrapped up with a discussion about escaping and quoting.

In the next chapter, we’ll talk about variables and pipelines. I’ll see you there.

1. Which of the following sets of metacharacters would cause the second command to run only if the first command runs successfully?
   1. ||
   2. &&
   3. |
   4. &
2. You want to run a command that contains the $ metacharacter, but you want the shell to interpret the metacharacter literally. How would you do that? (Choose two.)
   1. Precede the metacharacter with a /.
   2. Surround the text string that contains the metacharacter with a pair of single quotes.
   3. Precede the metacharacter with a \.
   4. Surround the text string that contains the metacharacter with a pair of double quotes.
   5. It’s not possible.
3. You’re using find to search for files on a FreeBSD system. To search through the current working directory, what must you do on FreeBSD that you don’t have to do on Linux?
   1. Use a dot to designate the search path.
   2. Nothing. The...

• Linux File Permissions Explained: https://www.redhat.com/sysadmin/linux-file-permissions-explained
• How to Use Bash Wildcards for Globbing?: https://www.shell-tips.com/bash/wildcards-globbing/#gsc.tab=0
• How to Recursively Search Directory Names in Linux: https://www.howtogeek.com/devops/how-to-recursively-search-directory-names-in-linux/
• Find Command in Linux: https://linuxize.com/post/how-to-find-files-in-linux-using-the-command-line/
• 10 Ways to Use the Linux find Command: https://www.redhat.com/sysadmin/linux-find-command
• What are Linux Metacharacters? Everything You Need to Know: https://www.makeuseof.com/what-are-linux-metacharacters/
• 6 Linux metacharacters I love to use on the command line: https://opensource.com/article/22/2/metacharacters-linux
• How to Use Your Bash Historyin the Linux or MacOS Terminal: https://www.howtogeek.com/44997/how-to-use-bash-history-to-improve-your-command-line-productivity/
• Navigating...

1. b
2. b and c
3. a
4. d
5. b

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