sed replaces text: sed -i 's/old/new/g' file edits in place. awk processes columns: awk '{print $1}' prints the first column. sort and uniq -c sort and count lines. Core tools for log analysis.
Text Tools
# sed — stream editor
sed 's/old/new/g' file.txt # replace all
sed '/^#/d' config.txt # delete comment lines
# awk — column processing
awk '{print $1, $3}' data.txt # print columns 1 and 3
awk -F',' '{sum+=$2} END{print sum}' data.csv
# sort and uniq
sort names.txt
sort -u names.txt # unique
cat log.txt | sort | uniq -c | sort -rn | head