Text Processing with Grep, Sed, and Awk

# Grep patterns
grep "pattern" file.txt
grep -r "error" /var/log/      # Recursive
grep -i "warning" file.txt     # Case insensitive
grep -v "exclude" file.txt     # Invert match
grep -E "pattern1|pattern2"    # Extended regex
grep -A 2 -B 2 "context"       # Show 2 lines before/after
grep -c "count" file.txt       # Count matches

# Sed stream editing
sed 's/old/new/g' file.txt     # Replace all occurrences
sed 's/old/new/2' file.txt     # Replace 2nd occurrence per line
sed '5,10d' file.txt           # Delete lines 5-10
sed -n '10,20p' file.txt       # Print lines 10-20 only
sed '/pattern/d' file.txt      # Delete lines matching pattern
sed -i.bak 's/old/new/' file   # In-place with backup

# Awk text processing
awk '{print $1}' file.txt      # Print first column
awk -F: '{print $1}' /etc/passwd # Custom delimiter
awk '/pattern/ {print $0}'     # Print matching lines
awk 'NR > 5 && NR < 10'        # Lines 6-9
awk '{sum+=$3} END {print sum}' # Sum column 3
awk '!seen[$0]++' file.txt     # Remove duplicates

# Combine commands
grep "error" log.txt | awk '{print $2, $5}' | sort | uniq -c
cat access.log | awk '{print $1}' | sort | uniq -c | sort -nr

# Cut columns
cut -d',' -f1,3 file.csv       # Comma delimited, fields 1&3
cut -f1-5 file.tsv             # Tab delimited

# Sort and unique
sort file.txt | uniq
sort -u file.txt               # Unique sort
sort -nr -k2 data.txt          # Numeric reverse by column 2

# Word count
wc -l file.txt                 # Line count
wc -w file.txt                 # Word count
wc -m file.txt                 # Character count

# Head and tail
head -20 file.txt
tail -f log.txt                # Follow (live view)
tail -n +100 file.txt          # Start from line 100