linuxexpert-practice-labs/labs/rhcsa/3-3-script-input-and-output/README.md

RHCSA 3.3: Script input and command output

Arguments, usage messages and exit codes, looping over all arguments, command substitution in file names, and adding up command output.

Before you start

The lab creates user student. Write each script where its task says and make it executable; the checks run them.

Tasks

1. Write /usr/local/bin/count-files that takes a directory and prints how many entries it holds, including hidden ones. With no argument or a non-directory, it prints usage: count-files DIRECTORY to standard error and exits 1. (Write the name literally: run from PATH, $0 is /usr/local/bin/count-files.)
2. Write /root/homes.sh that takes any number of user names and prints each user's home directory, or NAME: no such user. /root/homes.sh root nosuchuser student prints /root, the error line and /home/student.
3. Write /root/df-today.sh that saves the output of df -h / to a file named after today's date, such as /root/df-2026-10-20.txt, and run it.
4. Write /root/sumlines.sh that prints the sum of the line counts of every file given as an argument (just the number).

Hints

• $#, [ -d "$1" ], echo ... >&2, exit 1; ls -A "$1" | wc -l.
• for u in "$@"; getent passwd "$u" | cut -d: -f6.
• $(date +%F).
• wc -l <"$f", $((total + n)).