grep

Overview

The grep command searches input files for lines containing a match to a given pattern. It supports basic and extended regular expressions for pattern matching.

Syntax

grep [options] pattern [file...]

Common Options

Option Description
-i Ignore case
-v Invert match
-n Show line numbers
-l List matching files
-c Count matches
-r Recursive search
-w Match whole words
-x Match whole lines
-E Extended regex
-F Fixed strings
-A n After context
-B n Before context
-C n Context lines

Pattern Types

Type Description
Basic Simple patterns
Extended Advanced patterns
Fixed Literal strings
Perl Perl regex

Key Use Cases

  1. Text search
  2. Pattern matching
  3. File filtering
  4. Log analysis
  5. Code search

Examples with Explanations

Example 3: Count Matches

grep -c "pattern" file

Count matching lines

Common Usage Patterns

  1. Case insensitive:

    grep -i "pattern" file

  2. Multiple patterns:

    grep -e "pat1" -e "pat2" file

  3. Context lines:

    grep -C 2 "pattern" file

Regular Expressions

  1. Character classes
  2. Anchors
  3. Quantifiers
  4. Alternation
  5. Grouping

Additional Resources

Best Practices

  1. Quote patterns
  2. Use context
  3. Check options
  4. Verify matches
  5. Document usage

Performance Tips

  1. Use fixed strings
  2. Limit recursion
  3. Exclude dirs
  4. Buffer size
  5. Parallel grep

Troubleshooting

  1. Pattern syntax
  2. File permissions
  3. Binary files
  4. Character encoding
  5. Memory usage