Linux Essentials: Commands Every Engineer Must Know

# Print specific columns (tab/space-delimited)
awk '{print $1, $4}' access.log

# Sum a column
awk '{sum += $5} END {print "Total:", sum}' report.txt

# Filter rows by field value
awk '$9 == "500"' access.log

# Use custom field separator
awk -F: '{print $1, $3}' /etc/passwd

# Print lines between two patterns
awk '/START/,/END/' logfile.txt

sed -i 's/oldstring/newstring/g' file.conf    # in-place replace
sed -i.bak 's/foo/bar/g' file.conf            # with .bak backup
sed -n '10,20p' bigfile.txt                   # print lines 10–20
sed '/^#/d' config.conf                       # delete comment lines
sed 's/[[:space:]]*$//' file.txt              # strip trailing whitespace

# cut — slice fields from delimited input
cut -d: -f1,3 /etc/passwd           # fields 1 and 3
cut -c1-80 wide.txt                 # first 80 characters per line

# sort
sort -k2 -n file.txt                # numeric sort on column 2
sort -t, -k3 -rn data.csv           # CSV, col 3, reverse numeric
sort -u names.txt                   # sort + deduplicate

# uniq (input must be sorted first)
sort ips.txt | uniq -c | sort -rn   # count occurrences, rank by frequency

# wc
wc -l file.txt                      # line count
wc -w file.txt                      # word count
ls /var/log/*.log | wc -l           # count log files

# head / tail
head -n 50 app.log                  # first 50 lines
tail -n 100 app.log                 # last 100 lines
tail -f /var/log/syslog             # follow in real time
tail -F /var/log/app.log            # follow + reopen if rotated

dnf check-update                    # list available updates
dnf upgrade                         # apply all updates
dnf install httpd                   # install a package
dnf remove httpd                    # uninstall
dnf search "web server"             # search
dnf info httpd                      # package details
dnf history                         # transaction history
dnf history undo last               # rollback last transaction

rpm -qa | grep httpd                # list installed RPMs matching name
rpm -ql httpd                       # files owned by package
rpm -qf /usr/sbin/httpd             # which RPM owns a file

pkg update                          # refresh index
pkg upgrade                         # upgrade all
pkg install nginx                   # install
pkg delete nginx                    # remove
pkg search nginx                    # search
pkg info nginx                      # details
pkg which /usr/local/sbin/nginx     # which package owns a file