sed 'Nq;d' file.txt

echo "new content" | cat - file.txt > temp
mv temp file.txt

sed -i '1s/^/new content\n/' file.txt

sed -i '/^\s*$/d' file.txt

# N should be the target line number
sed -i 'Nd' file.txt

# N should be the target line number
sed -i 'Ns/.*/replacement-line/' file.txt

cat << EOF > file.txt
The current working directory is $PWD.
You are logged in as $(whoami).
EOF

Suppose we have two files: packages.fedora and packages.

packages.fedora:

autossh
bash-completion
bat
bc
borgmatic
bzip2
cmake
curl
diff-so-fancy
diffutils
dnf-plugins-core

packages:

bash-completion
bc
bzip2
curl
diffutils
dnf-plugins-core

To plain-print the lines that exist in packages.fedora but do not exist in packages:

comm -23 <(sort packages.fedora) <(sort packages)

Output:

autossh
bat
borgmatic
cmake
diff-so-fancy

• The comm command compares two sorted files line by line.
• The -23 flag is shorthand for -2 and -3.
• -2 suppresses column 2 (lines unique to packages).
• -3 suppresses column 3 (lines that appear in both files).

split -l 60 bigfile.txt prefix-

while read line; do
    echo "$line";
done </path/to/file.txt

cat urls.html | grep -Eo "(http|https)://[a-zA-Z0-9./?=_%:-]*"

To find all cron processes with ps aux:

ps aux | awk 'NR<2{print $0;next}{print $0 | grep "cron"}' | grep -v "awk"