Useful `grep` Snippets

Basic Search

Find a keyword in files:
```
grep "keyword" filename
```
Case-insensitive search:
```
grep -i "keyword" filename
```

Recursive Search

Search recursively in all files:
```
grep -r "keyword" /path/to/directory
```

Search recursively for a pattern while excluding specific directories:

grep -r --exclude-dir="dir_to_exclude" "keyword" /path/to/directory

Pattern Matching

Search using regular expressions:
```
grep -E "pattern1|pattern2" filename
```
Match whole words only:
```
grep -w "word" filename
```

Filter Files

Find files containing a pattern:
```
grep -l "keyword" /path/to/directory/*
```

Exclude files with certain extensions:

grep --exclude=*.log "keyword" /path/to/files/*

Output Control

Show line numbers with matches:
```
grep -n "keyword" filename
```
Show only the matched part of the line:
```
grep -o "pattern" filename
```

Contextual Search

Show lines before and after matches:

grep -C 3 "keyword" filename  # 3 lines of context

Show only lines before the match:
```
grep -B 3 "keyword" filename
```
Show only lines after the match:
```
grep -A 3 "keyword" filename
```

Advanced Usage

Search for patterns in compressed files:
```
zgrep "keyword" file.gz
```
Count occurrences of a pattern:
```
grep -c "keyword" filename
```
Invert the match (find lines without the pattern):
```
grep -v "keyword" filename
```

Combining with Other Commands

Pipe output to grep:
```
ps aux | grep "process_name"
```
Highlight matches in terminal output:
```
grep --color=always "keyword" filename
```

Debugging & Efficiency

Display file names along with matches in a directory:
```
grep -H "keyword" /path/to/directory/*
```

Limit search depth in recursive searches:

grep -r --include=*.txt "keyword" --max-depth=2 /path/to/directory

These snippets cover a wide variety of use cases. Let me know if you’d like more examples for specific scenarios!

Extended `grep` Snippets

File Type Filtering

Search only in specific file types:

grep --include=*.{c,h} "keyword" /path/to/directory/*

Exclude specific file types:

grep --exclude=*.{log,tmp} "keyword" /path/to/directory/*

Binary Files

Ignore binary files in search:

grep --binary-files=without-match "keyword" /path/to/directory/*

Search binary files:

grep --binary-files=text "keyword" /path/to/binary_file

Performance Optimizations

Limit output to first N matches:
```
grep -m N "keyword" filename
```

Search large files without buffering:

grep --line-buffered "keyword" largefile

POSIX Character Classes

Search for digits:
```
grep "[[:digit:]]" filename
```
Search for alphanumeric characters:
```
grep "[[:alnum:]]" filename
```

Custom Delimiters

Specify output delimiters:

grep -z "keyword" filename  # Null-separated output

Multiple Patterns

Search for multiple keywords (logical OR):

grep -e "keyword1" -e "keyword2" filename

Search for multiple patterns from a file:
```
grep -f patterns.txt filename
```

Miscellaneous

Print file offsets of matches:
```
grep -b "keyword" filename
```
Print the count of matches per file:
```
grep -c "keyword" filename
```
Suppress error messages:
```
grep "keyword" filename 2>/dev/null
```

Multiline Matching

Search across multiple lines (using Perl-compatible grep):
```
grep -Pzo "pattern1.*?pattern2" filename
```

Using grep with xargs

Find files and search within them:

find /path/to/search -name "*.txt" | xargs grep "keyword"

Combining grep with sed and awk

Replace pattern in grep results:

grep "pattern" filename | sed 's/pattern/replacement/g'

Count and format grep results:

grep "pattern" filename | awk '{count++} END {print "Total:", count}'

Environment Variables

Ignore case permanently by setting environment variable:
```
export GREP_OPTIONS='--ignore-case'
```

Highlight Matches in Less

Search while paging with highlights:
```
grep "keyword" filename | less -R
```

Useful grep Snippets