🔀 Redirections

Redirection allows you to control where input comes from and where output goes — beyond just printing to the terminal.

🧭 Input/Output Streams

Every process has three standard streams:

Stream	Number	Direction
stdin	0	Input
stdout	1	Output
stderr	2	Errors

By default: - stdin reads from keyboard - stdout prints to terminal - stderr prints to terminal

But you can redirect any of them.

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➡️ Redirecting Output

Send output to a file instead of terminal:

$ ls > listing.txt

Append to a file:

$ date >> log.txt

Redirect both stdout and stderr:

$ command > output.log 2>&1
# or shorter:
$ command &> output.log

Redirect only stderr:

$ command 2> errors.log

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⬅️ Redirecting Input

Feed data into a command from a file:

$ wc < myfile.txt

Pass inline text using here-documents:

$ cat << EOF
Hello World
EOF

Useful in scripts:

mail recipient@example.com << EOF
Subject: Test Email

Body content here.
EOF

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🧪 Combining Redirections

You can combine multiple redirections in one line:

$ grep ERROR logs.txt > errors_found.log 2> grep_errors.log

This separates matched lines (stdout) from potential grep errors (stderr).

Also useful:

$ some_command 2>&1 | tee output_and_log.txt

This sends both output and errors through pipe while saving to a file.

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🧾 Summary

• Redirection lets you reroute I/O streams.
• Common operators: >, >>, <, <<, 2>, &>
• Combine with pipes (|) for powerful workflows.
• Always consider where data should flow in automated scripts.

👉 Continue to: Pipelines