Bash Text Processing

grep "error" log.txt          # basic search
grep -i "error" log.txt       # case-insensitive
grep -n "error" log.txt       # line numbers
grep -v "debug" log.txt       # inverse match
grep -c "error" log.txt       # count matches
grep -r "TODO" src/           # recursive search

sed 's/old/new/' file.txt          # find and replace
sed -i 's/old/new/g' file.txt     # in-place edit
sed '/^#/d' config.txt            # delete comments

awk '{print $1}' data.csv                      # print first column
awk '$3 > 100' data.csv                         # filter rows
awk -F: '{print $1, $3}' /etc/passwd           # custom delimiter
awk '{sum += $2} END {print sum}' sales.txt    # calculate sum

# Count errors per hour
grep "ERROR" app.log | awk '{print $1, $2}' | cut -d: -f1,2 | sort | uniq -c

# Find top 10 IPs from access log
awk '{print $1}' access.log | sort | uniq -c | sort -rn | head -10