How to replace the word “Gun” with “Pen” in the first 100 lines of a file?

Display all the files in current directory sorted by size?

ls -l | grep ‘^-‘ | awk ‘{print $5,$9}’ |sort -n|awk ‘{print $2}’

How to reverse a string in unix?

echo “java” | rev

Explain iostat, vmstat and netstat?

Iostat: reports on terminal, disk and tape I/O activity. Vmstat: reports on virtual memory statistics for processes, disk, tape and CPU activity. Netstat: reports on the contents of network data structures.