[Linux] Bash grep Usage: Search for patterns in text

Overview

The grep command is a powerful text search utility in Unix/Linux systems. It allows users to search for specific patterns within files or input streams, making it an essential tool for developers, system administrators, and anyone working with text data.

Usage

The basic syntax of the grep command is as follows:

grep [options] [pattern] [file...]

Common Options

• -i: Ignore case distinctions in both the pattern and the input files.
• -v: Invert the match, showing only lines that do not match the pattern.
• -r or -R: Recursively search through directories.
• -n: Show line numbers along with matching lines.
• -l: List only the names of files with matching lines, not the lines themselves.
• -c: Count the number of matching lines instead of displaying them.

Common Examples

Here are some practical examples of using grep:

1. Basic search in a file:

   grep "error" logfile.txt
   

   This command searches for the term “error” in logfile.txt and displays all matching lines.

2. Case-insensitive search:

   grep -i "warning" logfile.txt
   

   This will find “warning”, “Warning”, “WARNING”, etc., in logfile.txt.

3. Search recursively in a directory:

   grep -r "TODO" /path/to/project/
   

   This command searches for the term “TODO” in all files within the specified directory and its subdirectories.

4. Count matching lines:

   grep -c "success" logfile.txt
   

   This will output the number of lines that contain the word “success” in logfile.txt.

5. Show line numbers with matches:

   grep -n "main" source.c
   

   This command will display the line numbers along with lines containing “main” in source.c.

Tips

• Use grep in combination with other commands using pipes to filter output effectively.
• Regular expressions can enhance your search patterns, allowing for more complex queries.
• When searching large files, consider using less in combination with grep for easier navigation of results:

  grep "pattern" largefile.txt | less