Editing Files

4. Editing Files#

Learning Goals

After this lesson, you should be able to:

Explain the difference between binary and plain text files
Explain what a text editor is
In the CLI:
- Edit files with a text editor
- Copy, move, and delete files

The shell commands we’ve covered so far give you ways to navigate between directories and inspect the contents of files. You can also use the CLI to edit files directly. This chapter explains one way to edit files with the CLI. It also introduces the final piece of the file browsing experience: how to copy, move, and delete files.

4.1. Text Editors#

A text editor is a computer program designed to edit files that contain plain text, free of images and other kinds of data. This reflects the fact that text editors originated in the CLI, although now text editors for GUIs are also available.

Text editors display the contents of a file faithfully and efficiently, with minimal processing. They stand in contrast to word processors (such as Microsoft Word), where you can freely mix text with graphical formatting, images, and other data, but what you see on the screen is a heavily processed version of what’s actually stored in the file. This minimalisim makes text editors useful for editing files that do not normally include formatting, such as code, and for examining the true contents of files, especially if their format is intended to be human-readable.

Plain Text vs. Binary

Ultimately, computers represent all data as numbers. They use a binary number system, where numbers are made up of the bits 0 and 1 rather than the digits 0 through 9 in the familiar decimal number system.

To represent text on a computer, we can encode each symbol as a specific number; the number represents the symbol. People have come up with many different standards for doing this. For instance, in the ASCII standard, which was designed for languages that use the Latin alphabet, 65 represents the letter A, 66 represents the letter B, 97 represents the letter a, and so on. Nowadays, most people use the UTF-8 standard, a superset of ASCII designed to support all languages.

When we say that files or data are “plain text,” we mean that they can be decoded with some well-known standard into text that’s intelligible. We refer to files and data that cannot be decoded this way as “binary.” Note that this is a reuse of the word in a closely related but distinct way from how we defined it previously.

Examples of plain text files include text files (.txt), Markdown files (.md), source code files for most programming languages (.R, .py, and many more), and human-readable data files (.csv, .json, and more). Plain text files can be opened in any text editor.

Examples of binary files include image files (.jpg, .png, and more), audio and video files (.mp3, .mp4, and more), data files (.rds, .pickle, .hd5, and more), and executable programs (.exe, .o, .so, and more). To open a binary file, you generally need to have special software to decode the contents into something meaningful.

You can see how all of this works if you try to open a binary file with a text editor. For example, if you open the cool_hair_selfie.jpg image included with the files from Section 3.4 in a text editor, you’ll see something like this:

ÿØÿà^@^PJFIF^@^A^A^A^D°^D°^@^@ÿþ^@^SCreated with GIMPÿÛ^@C^@^C^B^B^C^B^B^C^C^C^C^    D^C^C^D^E^H^E^E^D^D^E
^G^G^F^H^L
^L^L^K
^K^K^M^N^R^P^M^N^Q^N^K^K^P^V^P^Q^S^T^U^U^U^L^O^W^X^V^T^X^R^T^U^TÿÛ^@C^A^C^D^D^E^D    ^E▷^E^E▷ ^T^M^K^M^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T    ^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^T^TÿÂ^@^Q^H^Bw^AÃ^C^A^Q^@^B^Q^A^C^Q^AÿÄ^@^\^@^@^    B^C^A^A^A^A^@^@^@^@^@^@^@^@^@^B^C^A^D^E^F^@^G^HÿÄ^@^X^A^@^C^A^A^@^@^@^@^@^@^@^@^@    ^@^@^@^@^A^B^C^DÿÚ^@^L^C^A^@^B^P^C^P^@^@^Aø¶W^C<94>*<84>1^R<85>(^BcSv<94>é+Ä¾ª%^P    *ß<99>^S/L4j<89>ò^\é<93>0ß¥<90><96>;6ê¥,(<97>'6áµ^H^PÊg^HÓ]<8c>^KPï§KD¬ä<82>F<9a>    ^BÝ¼<87>'êuÃR^DQ<83>yØÑÖ<90>&@$^VÆ[<98>^nÖ­^PNQ-<94><9e>°Ósj<88><86>EÑ0^A²NkÉ<9d>    ¶hV<97>(ò<98>³Ù«2>ê«^ZÅ#Ò<9a><9f><98>Z^A<8a>0³uêe<8c><9c>¯hêS<9b>g<98>Cn<8d>^Y<8f    >ÎHxºAh^B^Nd-<9b>`<97><91>^R<84>^[»^DÇ9$6<98>Êrs½BG<94><82>@Ø!<92>7J^hÁì¬Ü6É<95>k    P¦ä6^N$

It’s a complete mess! It looks like this because the text editor does its best to decode the file as text, but since (most of) the file isn’t text, most of the decoded symbols actually represent something else. As a result, it’s generally not a good idea to edit binary files with a text editor.

As a final note, word processors, like Microsoft Word, add an interesting twist to all of the above. Word documents are actually comprised of a number of different, associated files under the hood. It’s technically possible to alter the text of such files with a text editor, but finding the right place to make a change is difficult, and it’s more convenient to use a program made to to interact with them.

Many different text editors exist, including several free and open-source options. A few popular CLI text editors are:

nano (and its predecessor Pico), a straightforward text editor with few features beyond displaying and editing text.
Vim (and its predecessor vi), a text editor designed to be customizable and extensible. It has many features that make it easier to edit code, such as search-and-replace, keyboard shortcuts, and syntax highlighting. Vim is also infamous for being difficult to learn because its interface consists of several different “modes.”
Emacs, another text editor designed to be customizable and extensible. It has many of the same features as Vim, and is also somewhat difficult to learn, although its interface is more like a word processor.

For the remainder of this reader, we’ll focus on nano (and Pico).

4.1.1. Nano & Pico#

Important

On Windows, nano is included with Git Bash.

On macOS, some versions have nano and some versions have Pico. You can use either one to follow along with the subsequent sections.

On Linux, nano is included with most distributions. If it’s missing, you can install it with your distribution’s package manager.

Let’s use nano to create a new text file in the 2026_intro-cmd directory you created in Section 2.4. To get started, change the working directory to that directory:

cd ~/2026_intro-cmd

We’ll make a file called hello.txt. You can open a file with nano by putting the name of or path to the file after the nano command. This will work even for files that don’t exist yet. Most other CLI text editors also work this way. Go ahead and open hello.txt with nano:

nano hello.txt

Once nano opens the file, you can type in or delete text, and use the arrow keys to move the cursor, as you would in a word processor. For this example, type in Hello world! on the first line of the file.

When you’re done editing, you can press Ctrl + o to save the file. nano will ask you to confirm that you want to save the file by pressing Enter or Return. After saving the file, you can press Ctrl + x to exit nano.

Tip

nano displays all of its keyboard shortcuts at the bottom of the screen. In the dislpay, it uses ^ to mean the Ctrl key. The keyboard shortcuts in nano are not case-sensitive.

Back at the CLI, use the head or cat command to check that the new hello.txt file contains what you wrote:

cat hello.txt

Hello world!

As another example, let’s look at the README.md file included in example-files.zip (Section 3.4). To open the file in nano:

nano example-files/README.md

The contents should look familiar from when you printed the file with head, but now you can edit the file if you’d like.

A text editor is an essential tool for anyone working with the CLI. It not only provides a way to edit text files, but also a way to inspect files whether or not they contain text. After file browsing commands, your text editor is likely the CLI command you will use the most.

Tip

If you want a text editor that’s full-featured but not much harder to learn than nano, check out Micro.

4.2. Moving & Deleting Files#

Section 2 explained how to use the CLI to browse through files and directories on your computer, but we left out one important detail: how to copy, move, and delete things. We’ll cover commands for all of those in this section.

Let’s make a copy of the hello.txt file you just created. You can use the cp command to make a copy. It requires two arguments: the path to the original file and the path to the copy (which the command will create). For the copy of hello.txt, let’s use the name another_hello.txt. So the command to make the copy is:

cp hello.txt another_hello.txt

Check with ls that there’s now a new file in the directory called another_hello.txt:

ls

another_hello.txt  data  example-files  example-files.zip  hello.txt

If you open another_hello.txt with a text editor or print it with head or cat, you should see that it’s exactly the same as hello.txt. Congratulations, you’ve made a copy!

The mv command moves a file to a different place. Note that renaming a file is equivalent to moving the file, so this command is also useful for renaming files. The syntax of the mv command is similar to the cp command. It requires two arguments: the path to the original file and the path to the destination. Try moving another_hello.txt to a_sincere_hello.txt:

mv another_hello.txt a_sincere_hello.txt

Now the directory looks like this:

ls

a_sincere_hello.txt  data  example-files  example-files.zip  hello.txt

If you want, you can also inspect a_sincere_hello.txt to make sure that its contents are the same.

Finally, let’s clean up by removing the a_sincere_hello.txt file. You can remove a file with the rm command. Be careful with this command, as there is no undo—removing a file is permanent and irreversible. Go ahead and remove a_sincere_hello.txt:

rm a_sincere_hello.txt`

Take one last look at the contents of the directory:

ls

data  example-files  example-files.zip  hello.txt

The a_sincere_hello.txt file is gone.

Caution

Like many shell commands, there’s no undo for the cp, mv, and rm commands. They’re also relatively mute, printing nothing or little to indicate what they’re doing. These characteristics make it easy to accidentally overwrite or delete a file.

If you’re worried about making mistakes, you can put these commands in interactive mode by passing the -i or --interactive flag. In interactive mode, the commands will prompt you with a yes/no question any time they might overwrite or delete a file.

Note

The cp, mv, and rm commands can also copy, move, and remove directories. The mv command can do this by default. For the cp and rm commands, you have to set the -r or --recursive flag in order for them to operate on directories.

Unlike rmdir, the rm -r command can delete directories even if they contain files.

4.3. Reference: Editing Commands#

Here’s a summary of the commands we covered in this chapter:

Command	Description	Examples
`nano`	Opens the nano text editor.	`nano my_file.txt`
`cp`	Makes a copy of a file or directory.	`cp my_file.txt my_copy.txt`
`mv`	Moves (or renames) a file or directory.	`mv my_file.txt my_file_renamed.txt`
`rm`	Removes a file or directory.	`rm my_file.txt`

4.4. A Final Note#

Although we’ve only scratched the surface of what you can do with the command line, the commands and underlying concepts we’ve discussed here should prepare you to continue using and learning about the CLI. In doing so, our hope is that you’ll become a more confident and experienced computer user. If questions do arise, DataLab offers support across all levels of experience. See our website for details about office hours, as well as other resources and events for learners. Happy scripting!