Command Combos

Combining Linux Commands

In Linux and Unix-based systems, it's common to combine multiple commands to create powerful workflows and data manipulations. This is often done using pipes (|), redirection, and logical operators.

Using Pipes (|)

A pipe is used to send the output of one command as the input to another command. This allows you to chain commands together.

Example: cat and grep

• cat prints the contents of a file.
• grep searches for a pattern in the input it receives.

To print the contents of a file and search for a specific word, you can use:

cat file.txt | grep "search-term"

In this example, cat sends the file's content to grep, which searches for "search-term" and displays matching lines.

Example: ls and grep

If you want to list only files that contain a certain keyword:

ls | grep "keyword"

Example: Excluding Lines with cat and grep

You can use cat * to print all lines of every file in a directory and grep -v to exclude lines that contain a specific keyword:

cat * | grep -v "keyword"

Combining with Redirection (>, >>, <)

Redirection allows you to send the output of a command to a file, or to take input from a file.

Example: Saving grep Output to a File

You can save the results of a search to a file by redirecting the output using >:

cat file.txt | grep "search-term" > results.txt

Example: Appending Output to a File

If you want to append the result instead of overwriting:

cat file.txt | grep "search-term" >> results.txt

Using Logical Operators (&&, ||)

You can use logical operators to run multiple commands conditionally.

• && runs the second command only if the first succeeds.
• || runs the second command only if the first fails.

Example: &&

To check if a file exists and then delete it if it does:

[ -f file.txt ] && rm file.txt

Example: ||

To attempt a command and display a message if it fails:

mkdir new_folder || echo "Failed to create directory"

Combining Pipes, Redirection, and Logical Operators

You can combine all of these together for more complex operations.

Example: Searching and Saving to a File Only If Results Are Found

cat file.txt | grep "search-term" > results.txt && echo "Results saved" || echo "No results found"

In this example:

• The command searches for "search-term".
• If it finds results, it saves them to results.txt and echoes "Results saved".
• If no results are found, it echoes "No results found".

Conclusion

By combining commands with pipes, redirection, and logical operators, you can create highly efficient and customizable workflows in your terminal. Mastering these combinations allows you to perform complex tasks with simple one-liners.