Post

Introduction to the Terminal

This post will take you from couch to the command line in 15mins!

Posted Updated
By the end of this post, you will understand this screenshot!
By the end of this post, you will understand this screenshot!
By Matt Popovich
15 min read

Disclaimer

Command line, command prompt, shell, terminal, console, etc. can sometimes be used interchangeably. I will be using them interchangeably in this article. Normally, they are all referring to a window in which you input text commands and receive text output.

There are a lot of intricacies in the terminal. You might call them “quirks” or “features”. You will never learn them all and some of them still stump me to this day. Half of the battle is just knowing which features exist. If you know it exists (even though you might not remember exactly how to use a feature), any search engine will get you there (“How do I copy a file in the terminal”). If you can think it, someone has probably done it in the terminal.

Also, the terminal does not add a newline between commands. I have added that in hopes of making things easier to read.

Opening the Terminal

The terminal is opened differently depending on your operating system:

  • Windows
    • Search for the program “Command Prompt”
  • Mac
    • Search for the program “Terminal.app”
  • Linux
    • Search for the program “Terminal”
    • Or via the keyboard shortcut ctrl + alt + t

Note that most of this post will not work in Windows’ Command Prompt. The Command Prompt uses a different language compared to Mac and Linux’s terminals. See this answer for additional information.

More detailed information via effective-shell.com (with pictures!).

How to Use

The terminal is made up of three possible things:

1

$ program -flags arguments

A $ or # are common hints that this line is meant to be ran in a terminal

  • program is a small executable that resides on your system
    • Required
    • Most common ones can be found in /bin
    • Also referred to as: executable, script, binary, command, etc.
  • flags are normally either one letter or a full word that activate certain capabilities in a program
    • Optional
  • arguments are information given to a program for it to act upon (just like function arguments)
    • Optional
    • Sometimes shortened to just args

The terminal is case-sensitive.

Example Use

ls

ls = a program used to list files

1
2
3
4
5

$ ls
Applications   Movies
Desktop        Music
Documents      Pictures
Downloads

We can add the flag -l = list files in the long format

1
2
3
4
5
6
7
8
9

$ ls -l
total 8
drwx------@   5 mattpopovich  staff          160 Nov  5  2021 Applications
drwxr-xr-x+  44 mattpopovich  staff         1408 Apr 15 20:37 Desktop
drwx------@  32 mattpopovich  staff         1024 Jul 19  2023 Documents
drwx------@ 430 mattpopovich  staff        13760 May 14 10:08 Downloads
drwx------   22 mattpopovich  staff          704 Apr  9 01:32 Movies
drwx------+   5 mattpopovich  staff          160 Oct 10  2022 Music
drwx------+   7 mattpopovich  staff          224 Apr 13 10:14 Pictures

ls supports multiple flags. We can also include -h = list files in a more human readable format

Note that this gives you the size of the file. This does not give you the size of the files in the folder!! (Use du for that)

1
2
3
4
5
6
7
8
9

$ ls -lh
total 8
drwx------@   5 mattpopovich  staff         160B Nov  5  2021 Applications
drwxr-xr-x+  44 mattpopovich  staff         1.4K Apr 15 20:37 Desktop
drwx------@  32 mattpopovich  staff         1.0K Jul 19  2023 Documents
drwx------@ 430 mattpopovich  staff          13K May 14 10:08 Downloads
drwx------   22 mattpopovich  staff         704B Apr  9 01:32 Movies
drwx------+   5 mattpopovich  staff         160B Oct 10  2022 Music
drwx------+   7 mattpopovich  staff         224B Apr 13 10:14 Pictures

Note how the size of the files changed from being displayed in bytes to being converted to B, KB, GB, etc.

If we were only interested in one specific file or folder, we can give ls an argument for which file or folder to list:

1
2
3
4
5
6
7

$ ls -lh Documents
-rw-r--r--@  1 mattpopovich  staff   774K Oct  1  2022 img1.png
-rw-r--r--@  1 mattpopovich  staff   399K Oct  1  2022 img2.png
-rw-r--r--@  1 mattpopovich  staff   404K Oct  1  2022 img3.png

$ ls -lh Documents/img1.png
-rw-r--r--@  1 mattpopovich  staff   774K Oct  1  2022 img1.png

Note that this showed us the contents of what was inside that folder, or if it was a file, it showed us information about only that file.

If we wanted to see more detailed information about a folder (without listing its contents), we can use the -d flag:

1
2
3
4
5

$ ls -lhd Documents
drwx------@ 32 mattpopovich  staff   1.0K Jul 19  2023 Documents

$ ls -l -h -d Documents
drwx------@ 32 mattpopovich  staff   1.0K Jul 19  2023 Documents

Here, we add the -d flag to tell ls to show us information about the directory (and not what is inside the directory) named Documents. Also note that single character flags can be together (-lhd) or separate (-l -h -d).

man

man = Display manual documentation pages

Before we go too much further, I should mention the man command.

Give a man a fish, and you feed him for a day. Teach a man to fish, and you feed him for a lifetime.

This command displays documentation for the argument you pass to it. This is what it looks like if you run it with an argument of ls (the command I explained above):

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38

$ man ls
LS(1)                     General Commands Manual                    LS(1)

NAME
     ls – list directory contents

SYNOPSIS
     ls [-@ABCFGHILOPRSTUWabcdefghiklmnopqrstuvwxy1%,] [--color=when]
        [-D format] [file ...]

DESCRIPTION
     For each operand that names a file of a type other than directory, ls
     displays its name as well as any requested, associated information.
     For each operand that names a file of type directory, ls displays the
     names of files contained within that directory, as well as any
     requested, associated information.

     If no operands are given, the contents of the current directory are
     displayed.  If more than one operand is given, non-directory operands
     are displayed first; directory and non-directory operands are sorted
     separately and in lexicographical order.

     The following options are available:


     -@      Display extended attribute keys and sizes in long (-l)
             output.

     -A      Include directory entries whose names begin with a dot (‘.’)
             except for . and ...  Automatically set for the super-user
             unless -I is specified.

     -B      Force printing of non-printable characters (as defined by
             ctype(3) and current locale settings) in file names as \xxx,
             where xxx is the numeric value of the character in octal.
             This option is not defined in IEEE Std 1003.1-2008
             (“POSIX.1”).
[...]

Note that once you run man, a new “window” in the terminal opens. You can advance to the next line with the enter key, up and down errors, or even scrolling (if enabled). Press q (quit) to exit. q to exit is common in other programs (vi) as as we will find out.

If you scroll down in that man page, you will find information about the flags that I explained above:

1
2
3
4
5
6
7
8
9

     -d      Directories are listed as plain files (not searched recursively).
    [...]
     -h      When used with the -l option, use unit suffixes: Byte, Kilobyte,
             Megabyte, Gigabyte, Terabyte and Petabyte in order to reduce the
             number of digits to four or fewer using base 2 for sizes.  This
             option is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).
    [...]
     -l      (The lowercase letter “ell”.) List files in the long format,
             as described in the The Long Format subsection below.

I will leave the other flags as an exercise for the reader 😉

glob

Something else that’s neat about the terminal is that it’s created by programmers, for programmers. It has a lot of very powerful “shortcuts” that can be used. For example:

1
2
3
4

$ ls -ld D*
drwxr-xr-x+  44 mattpopovich  staff   1408 Apr 15 20:37 Desktop
drwx------@  32 mattpopovich  staff   1024 Jul 19  2023 Documents
drwx------@ 430 mattpopovich  staff  13760 May 14 10:08 Downloads

Here, we use the glob wildcard * to list all directories that start with D. Very handy whenever you are in a folder with lots of files!

Also worth noting that the terminal supports tab completion!! This is a lifesaver and can save tons of time (particularly when typing in long filenames). Basically, whenever you are typing a command or a file path, just press tab in the middle of the word and if the terminal finds a match for it, it will auto-complete the rest of the word. If there are multiple words that would match the completion, pressing tab twice will show all possible matches.

1
2
3
4
5
6
7
8

$ ls D<tab><tab>
Desktop/    Documents/  Downloads/

$ ls Do<tab><tab>
Documents/  Downloads/

$ ls Doc<tab>
$ ls Documents

pwd

pwd = present working directory

This command tells you where your terminal session is currently located:

1
2

$ pwd
/users/mattpopovich

cd

cd = change directory

Your terminal will normally show what directory you are currently in before each command. (I won’t always show it in this post unless I think it is needed). This helps keep you oriented to what folder you are currently operating in!

The cd command lets you change which directory you are currently located in:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

/users/mattpopovich $ ls
Applications   Movies
Desktop        Music
Documents      Pictures
Downloads

/users/mattpopovich $ cd Music

/users/mattpopovich/Music $ ls
01_Not_Like_Us-Kendrick_Lamar.mp3

/users/mattpopovich/Music $ cd /users/mattpopovich

/users/mattpopovich $ ls
Applications   Movies
Desktop        Music
Documents      Pictures
Downloads

/users/mattpopovich $ ls Music
01_Not_Like_Us-Kendrick_Lamar.mp3

Two important symbols in the shell are the tilde ~ and dot-dot ...

  • ~ represents your home directory (/users/mattpopovich)
  • .. represents the parent directory

The above console session could also be (and most often is) represented by:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

~ $ ls
Applications   Movies
Desktop        Music
Documents      Pictures
Downloads

~ $ cd Music

~/Music $ ls
01_Not_Like_Us-Kendrick_Lamar.mp3

~/Music $ cd ..

~ $ ls
Applications   Movies
Desktop        Music
Documents      Pictures
Downloads

~ $ ls Music
01_Not_Like_Us-Kendrick_Lamar.mp3

Notice that /users/mattpopovich is being displayed as ~. Also note that we went “up” to the parent folder via cd .. instead of cd /users/mattpopovich.

touch

touch = change file access and modification times

Personally, I never use this command for its intended purpose. I only use it for creating new, empty files.

1
2
3
4
5
6
7
8
9
10
11
12
13

$ man touch
[...]
The touch utility sets the modification and access times of files.  If any file
     does not exist, it is created with default permissions.
[...]

$ ls

$ touch test_file.txt

$ ls -l
total 0
-rw-r--r--  1 mattpopovich  staff  0 Feb 31 20:42 test_file.txt

mkdir

mkdir = make directories

This command will make an empty directory/folder with a name of the argument that you specify:

Note that # denotes the beginning of a “comment”. Anything after # is ignored by the terminal. I’m using it below to help give additional context.

1
2
3
4
5
6
7
8
9
10

$ ls -l
total 0
-rw-r--r--  1 mattpopovich  staff  0 Feb 31 20:42 test_file.txt

$ mkdir test_folder

$ ls -l               # Confirming that a new folder was created!
total 0
-rw-r--r--  1 mattpopovich  staff   0 Feb 31 20:42 test_file.txt
drwxr-xr-x  2 mattpopovich  staff  64 Feb 31 20:49 test_folder

mv

mv = move files

Now that we know how to make files and folders, let’s learn how to customize things a bit.

This command will move the first argument to the second argument. mv source destination. It can be used to move files into a folder or even “rename” files by moving them to a new name.

Let’s move some files around:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

$ ls
test_file.txt test_file2.txt test_file3.txt test_folder

$ ls test_folder              # Nothing printed below means the folder is empty

$ mv test_file.txt test_folder

$ ls test_folder              # test_file.txt was successfully moved into test_folder
test_file.txt

$ ls
test_file2.txt test_file3.txt test_folder

$ mv test_file* test_folder   # Move any file that starts with "test_file" into test_folder

$ ls
test_folder

$ ls test_folder              # We have moved all of our files into test_folder
test_file.txt test_file2.txt test_file3.txt

You can also specify more than one source and they will all be moved to the destination mv source1 source2 destination:

1
2
3
4
5
6
7

$ ls
test_file.txt test_file2.txt test_file3.txt test_folder

$ mv test_file.txt test_file2.txt test_file3.txt test_folder

$ ls test_folder
test_file.txt test_file2.txt test_file3.txt

Here, we accomplished the same effective thing but without the glob from above (mv test_file* test_folder). Although I would argue that the glob was probably easier.

Now, let’s rename some files (by moving them to a new name):

1
2
3
4
5
6
7
8
9
10
11
12
13

$ ls
test_folder

$ ls test_folder
test_file.txt

$ mv test_folder testing_folder

$ ls                    # Confirming successful "rename"
testing_folder

$ ls testing_folder     # Folder contents hasn't changed
test_file.txt

cp

cp = copy files

This is used the same as the mv command above, but it copies the files instead of moving them.

This command will copy the first argument to the second argument. cp source destination:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

$ ls
test_file.txt test_file2.txt test_file3.txt test_folder

$ ls test_folder

$ cp test_file.txt test_folder    # Copy test_file.txt into test_folder

$ ls
test_file.txt test_file2.txt test_file3.txt test_folder

$ ls test_folder                  # Copy was successful, test_file.txt is in both locations
test_file.txt

$ cp test_file* test_folder       # Copy all files that begin with test_file to test_folder

$ ls
test_file.txt test_file2.txt test_file3.txt test_folder

$ ls test_folder                  # Copy was successful
test_file.txt test_file2.txt test_file3.txt

rm

rm = remove

  • -d = remove directory
  • -R = recursively remove things in a directory. Implies the -d option
  • -r = Equivalent to -R

This command will remove files and folders

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

$ ls
test_file.txt test_folder

$ ls test_folder

$ rm test_file.txt

$ ls
test_folder

$ rm test_folder
rm: test_folder: is a directory

$ rm -d test_folder   # -d flag will remove an empty directory

$ ls


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

$ ls
file1 test_folder

$ ls test_folder
file2

$ ls *
file1

test_folder:
file2

$ rm -d test_folder
rm: test_folder: Directory not empty

$ rm -r test_folder   # -r flag will remove a non-empty directory

$ ls
file1

cat

cat = concatenate and print files

This command will print the contents of a file

1
2
3
4
5

$ ls -lh
-rw-r--r--  1 mattpopovich  staff    38B Nov 13 18:50 test_file.txt

$ cat test_file.txt
This is the contents of test_file.txt

Text Editors

There are multiple “editors” available to use in the command prompt. Engineers will have their own (sometimes strong) preference as to which one you should use. I just use vi and for no particular reason other than I know how to use it and I don’t use it enough to warrant learning other editors. The other major editors are emacs and nano.

vi / vim

vi = visual

vim = vi improved

1
2
3

$ ls

$ vi text_file.txt

After typing vi text_file.txt and hitting enter, we are kicked into the editor. It can be a little daunting at first but here are some of vis commands. These are entered in once vi is open. These are not command line arguments.

  • i = go into “insert” mode
    • After pressing i on the keyboard, you can now type and modify text in the file
    • You can tell you are in insert mode by the -- INSERT -- text at the bottom of your screen
  • Esc = exit “insert” mode
    • When you are out of insert mode, you can type commands but cannot modify text
  • vi commands
    • / = search for text
      • Ex. /text + Enter will bring you to the next occurrence of text in the file
      • Then press n to go to the next occurrence of text in the file
      • Or press N to go to the previous occurrence of text in the file
    • gg = go to the first line in the file
    • GG = go to the last line in the file
    • dd = delete the current line that the cursor is on
    • :q = quit the file
    • :q! = quit the file and discard changes
    • :wq = save the file (write to disk) and then quit

Additional commands can be found here.

If it is installed on your system, you should try to run the vimtutor command from your terminal, which will start a tutorial of the basic Vim commands. Thanks, Stack Overflow!

Additional Resources

Outro

These are the very basics of the terminal. My next post will touch on more intermediate features for the terminal. Be sure to check back for that!

Blog, Not YouTube
bash big sur catalina cli how to linux mac monterey osx programming tech
This post is licensed under CC BY 4.0 by the author.

Comments powered by Disqus.