linuxexpert-practice-labs/labs/linux-terminal/1-2-search-compare-modify

Using Linux Terminal 1.2: Searching, comparing and changing files

grep and regular expressions, find with errors thrown away, sed with a backup, and diff.

Before you start

The lab creates user student (password Lab-Pass-1). Work as student (sudo -iu student), so ~ is /home/student. The lab removes the files the tasks create if they exist, and le-lab reset removes them again.

Tasks

1. Write the names of all users whose shell is /bin/bash to ~/bash-users.txt, one per line, and nothing else.
2. As student, find every regular file under /etc bigger than 100 KiB and save the list in ~/big-etc.txt, with any permission errors thrown away: none on the screen and none in the file.
3. Copy /etc/ssh/sshd_config to ~/sshd.copy, then use sed to change #Port 22 to Port 2222 in the copy, keeping a .bak of it. diff ~/sshd.copy.bak ~/sshd.copy shows just that one line changed.

Hints

• grep '/bin/bash$' /etc/passwd, then cut -d: -f1; compare wc -l with grep -c.
• find /etc -type f -size +100k, and 2>/dev/null for the errors.
• sed -i.bak 's/^#Port 22$/Port 2222/'; diff shows a c change.