Cron expression tester linux
Parse and show next 5 trigger times for a cron expression
systemd-analyze calendar '*/5 * * * *'
more linux
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Redirect stderr to file
command > /tmp/out.log 2> /tmp/err.log
Capture both streams
command 2>&1 | tee /tmp/all.log
Replace string in files recursively
grep -rl 'old_string' /etc/ | xargs sed -i 's/old_string/new_string/g'
Print specific columns with awk
awk '{print $1, $3}' /etc/passwd
Sum a column with awk
awk '{sum += $2} END {print sum}' file.txt