Bash grep Command - Search Text Using Patterns
Using the grep Command
The grep command is used to search for text patterns within files.
It's a powerful way to find specific text in large files or across many files.
Basic Usage
To search for a pattern in a file, use grep 'pattern' filename:
Example
grep 'shell' file.txt
A shell is a text-based interface that lets you talk to your computer.
There are different types of shells. Bash (Bourne Again SHell)Options
The grep command has options to change how it works:
-i- Search ignoring case differences (uppercase or lowercase)-r- Search through all files in a directory and its subdirectories-v- Find lines that do not match the pattern
Ignore Case
The -i option lets you search without worrying about case sensitivity.
Example: Ignore Case
grep -i 'shell' file.txt
Understanding Shells
A shell is a text-based interface that lets you talk to your computer.
There are different types of shells. Bash (Bourne Again SHell)Recursive Search
The -r option allows you to search through all files in a directory and its subdirectories.
Example: Recursive Search
grep -r 'search_term' /home/user/my_directory
/home/user/.my_secret_file:A shell is a text-based interface that lets you talk to your computer.
/home/user/.my_secret_file:There are different types of shells. Bash (Bourne Again SHell)
/home/user/.my_secret_file:Bourne Shell (sh): The original Unix shell, developed by Stephen Bourne.
/home/user/copy_of_my_file.txt:A shell is a text-based interface that lets you talk to your computer.
/home/user/copy_of_my_file.txt:There are different types of shells. Bash (Bourne Again SHell)
/home/user/myfolder/my_file.txt:A shell is a text-based interface that lets you talk to your computer.
/home/user/myfolder/my_file.txt:There are different types of shells. Bash (Bourne Again SHell)
/home/user/my_file.txt:A shell is a text-based interface that lets you talk to your computer.
/home/user/my_file.txt:There are different types of shells. Bash (Bourne Again SHell)Invert Match
The -v option finds lines that do not match the pattern.
Example: Invert Match
grep -v 'shell' my_file.txt
Understanding Shells
Using grep with Regular Expressions
Regular expressions allow you to search for complex patterns.
For example, grep '^[A-Za-z]' file.txt finds lines starting with a letter.
Example: Regular Expressions
grep '^[A-Za-z]' my_file.txt
Understanding Shells
A shell is a text-based interface that lets you talk to your computer.
There are different types of shells. Bash (Bourne Again SHell)
is popular because it's powerful and easy to use.Exercise?What is this?
Test your skills by answering a few questions about the topics of this page
Write the command to search for the term error in the file log.txt.
