Redirection

Objectives

By the end of this chapter, you should be able to:

• Explain what redirection is
• Explain the difference between >, >>, and <
• Use redirection to work more effectively in Terminal

💡 Why this matters: Most Terminal output just prints to the screen and disappears. Redirection is how you capture it — into a file, or into another command — which is the foundation everything in the next lesson (piping) builds on.

Sending Output to a File

By default, a command’s output goes straight to your screen. Redirection lets you send it somewhere else instead — most often, into a file. Try it with echo:

echo Hello World > hello.txt
cat hello.txt

> took the text echo would normally print and wrote it into hello.txt instead. Now run this:

echo Hello Universe > hello.txt
cat hello.txt

hello.txt now says “Hello Universe” — the previous contents are gone. > always overwrites the whole file.

If you want to add to a file instead of replacing it, use >>:

echo Hello World >> hello.txt
cat hello.txt

Hello Universe
Hello World

That’s the whole distinction: > replaces, >> appends. This is also a fast way to drop a short note into a file without ever opening an editor.

Reading Input From a File

> and >> both send output out of a command. < goes the other direction — it feeds a file in as input. Take sort, which prints a file’s lines alphabetically. Given a file names.txt containing:

Bob
Tom
Jim
Amy

sort names.txt prints:

Amy
Bob
Jim
Tom

Combine all three operators and you can feed a file in, sort it, and write the result straight to a new file, all in one line:

sort < names.txt > sorted.txt

That reads names.txt in as input, sorts it, and writes the result to sorted.txt — no cat, no manual copy-paste.

Quick Reference

Try It

Redirection changes real files on disk, so run these yourself rather than in a sandbox:

1. Use > to write your name into a file called me.txt.
2. Use >> to add your favorite color as a second line, without erasing the first.
3. Create a file with three or four words, one per line, in any order. Use sort with < and > to write a sorted copy to a second file, without ever opening either file in an editor.

Recap

• > overwrites a file with a command’s output; >> appends instead.
• < feeds a file’s contents in as input to a command.
• Redirection is one-directional per operator — you can combine < and > on the same line to read from one file and write to another.

You’ve only used one command at a time so far. Next lesson: chaining multiple commands together with pipes.