Substitution

Replace first occurrence on each line

cat <<'EOF' | awk '{sub(/WARN/, "ALERT"); print}'
WARN disk usage 82% WARN inode usage 91%
WARN memory pressure detected
INFO service healthy
EOF

Replace ALL occurrences on each line

cat <<'EOF' | awk '{gsub(/WARN/, "ALERT"); print}'
WARN disk usage 82% WARN inode usage 91%
WARN memory pressure detected
INFO service healthy
EOF

Replace non-alphanumeric characters with underscores

printf '%s\n' "vault-01.inside.domusdigitalis.dev" "ise-pan:8443/admin" | awk '{gsub(/[^a-zA-Z0-9]/, "_"); print}'

Convert to lowercase

printf '%s\n' "VAULT-01" "ISE-PAN" "PFSENSE-GW" | awk '{print tolower($0)}'

Convert first field to uppercase

printf '%s %s\n' critical "disk full" warning "high latency" info "service ok" | awk '{print toupper($1), $2, $3}'

Strip leading/trailing whitespace

printf '  vault-01  \n\tise-pan\t\n   pfsense  \n' | awk '{gsub(/^[ \t]+|[ \t]+$/, ""); print}'

Remove ANSI escape codes from colored output

printf '\033[31mERROR\033[0m connection refused\n\033[33mWARN\033[0m timeout\n' | awk '{gsub(/\033\[[0-9;]*m/, ""); print}'

Replace field conditionally — mark high values

cat <<'EOF' | awk '{if($3>100) $3="HIGH"; print}'
vault-01 cpu 45
ise-pan cpu 230
pfsense mem 180
vyos disk 12
EOF