Pattern Matching with grep

The grep utility searches for patterns within files or directory trees.

grep "error" system.log
grep -i "failed" app.log          # Case-insensitive matching
grep -w "function" script.sh      # Whole word matches only
grep -e "warning" -e "alert" debug.txt  # Multiple pattern search
grep -n "TODO" src/               # Display line numbers
grep -v "test" results.txt        # Inverted matching
grep -r "config" ./               # Recursive directory search
grep -l "main" *.c                # List filenames with matches
grep -E "^[A-Z]" names.txt        # Extended regular expressions

File Discovery with find

Locate files based on name, type, timestamp, and ownership criteria.

find /var/www -name "*.html"
find /etc -type f                 # Regular files only
find /home -type d                # Directories only
find /usr -type l                 # Symbolic links only

# Time-based searches
find /tmp -amin -30               # Accessed within 30 minutes
find /config -cmin -60            # Changed within 1 hour
find /data -mmin -120             # Modified within 2 hours
find /logs -mtime -7              # Modified within 7 days

# Ownership-based searches
find /projects -user developer
find /shared -group engineering

Stream Editing with sed

Perform non-interactive text transformations on files and streams.

# Operation modes
sed -e 's/old/new/' input.txt     # Execute and display output
sed -n 'p' data.csv               # Suppress automatic printing
sed -i 's/foo/bar/' config.ini    # In-place file editing
sed -i.bak 's/pattern/replace/' file.txt  # Backup before editing
sed -f script.sed source.txt      # Commands from external file

# Editing commands
sed -i '3i\Inserted line' doc.md  # Insert before line 3
sed -i '5a\Appended line' notes.txt  # Append after line 5
sed -i '2d' temp.log              # Delete line 2
sed -i '4c\Replaced content' report.txt  # Replace line 4
sed -i 's/error/fixed/g' app.log  # Global substitution
sed -n '10p' largefile.txt        # Print specific line

Word Counting with wc

Generate statistics on lines, words, bytes, and characters.

wc report.txt
# Output format: lines  words  bytes  filename

wc -l source.py                   # Line count only
wc -w essay.md                    # Word count only
wc -c data.bin                    # Byte count only
wc -m unicode.txt                 # Character count only

Archive Management with tar

Create and extract archievs with optional compression.

tar -cvf archive.tar directory/   # Create verbose archive
tar -xvf archive.tar              # Extract verbose archive
tar -czvf backup.tar.gz /path     # Create gzipped archive
tar -xzvf backup.tar.gz           # Extract gzipped archive
tar -tf archive.tar               # List archive contents
# Note: The -f flag must precede the filename

Viewing File Extremities

Display the beginning or end of files with head and tail commands.

head -20 logfile.log              # First 20 lines
tail -50 error.log                # Last 50 lines
tail -f application.log           # Real-time file monitoring