Can you explain how to use shell's grep command to match a regex pattern?

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Yes, sure.

The grep command is used to search for text patterns in documents. To use grep command to match a regex pattern, follow these steps:

1. Open your terminal and type "grep" followed by the regular expression pattern you want to match.

2. Add the name of the file or directory you want to search after the pattern. For example, if you have a file named "sample.txt" in your current directory, you can search for a pattern "hello" in the file using the following command:

grep "hello" sample.txt

This command will search for any lines that contain the word "hello" in the "sample.txt" file.

1. You can also use regular expression pattern matching to search for more complex patterns. For example, if you want to search for lines that start with the letter "t" followed by any three characters and end with the letter "r", you can use the following pattern:

grep "^t...r$" sample.txt

This command will search for any lines in the "sample.txt" file that match the pattern.

1. If you want to search for a pattern in multiple files in a directory or a folder, you can use the wildcard character "*". For example, if you want to search for the word "hello" in all text files in the "Documents" directory, you can use the following command:

grep "hello" Documents/*.txt

This command will search for the word "hello" in all text files that end with ".txt" in the "Documents" directory.

Overall, the grep command is a powerful tool for searching for specific text patterns in documents using regular expressions.