Create, read and edit text files

Use cat for short files, less for long ones, and head/tail for the start or the end.

$cat /etc/hostname
server1.example.com
$cat -n /etc/fstab
$less /var/log/messages
$head -n 5 /etc/passwd
$tail -n 20 /var/log/secure
#tail -f /var/log/messages

vim has modes. In normal mode keys are commands. In insert mode keys write text. In command mode (after :) you save and quit.

$vim notes.txt
$vimtutor

Every vim user must know these four commands.

Most editing happens in normal mode with short key commands. A number before a command repeats it (3dd = delete 3 lines).

Search with /, replace with :s. With % the replace works in the whole file.

#cp -a /etc/ssh/sshd_config /root/sshd_config.test
#vim /root/sshd_config.test

nano is easier for beginners: you type at once, and the key commands are shown at the bottom (^ = Ctrl).

$nano /tmp/test.txt
#dnf install nano

For short files you do not need an editor: use echo with > / >>, or a here document (<<EOF).

$echo "server1" > hostlist.txt
$echo "server2" >> hostlist.txt
#cat > /etc/motd << 'EOF'
Authorized users only.
Problems? Call the IT desk: ext. 4040
EOF
#tee /etc/sysctl.d/90-test.conf << 'EOF'
vm.swappiness = 10
EOF

$echo "nameserver 192.168.122.1" | sudo tee -a /etc/resolv.conf