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TIL - Today I Learned

Things I learned from colleagues, the internet or just out of curiosity.

• tail -f <logfile> | grep --line-buffered: filter logfile continuously while debugging a service or some ongoing process
• &<term> in less: show only lines matching filter in less pager
• ctrl+x ctrl+e in bash: opens default editor (specified with $EDITOR or $VISUAL) for specifying a prompt, will get executed on save+close (src, look for edit-and-execute-command).
• ctrl+r in bash: fuzzy search in bash history, press again for cycling through
• ctrl+x and ctrl+a on an action while interactive rebase: cycle through the rebase actions when interactively rebasing within an editor (git rebase -i)
• yes | dd oflag=/mnt/data iflag=fullblock oflag=direct bs=16M count=$((1024*1024/16)) status=progress: generate 1TB of non-random test data with storage backend speed, avoid buffering where possible
• go doc --all strings: local documentation of the go strings package
• du --summarize -h .: show summarized usage of a folder human friendly
• ag -G <filename-pattern> <search-pattern>: only search in files matching the filename pattern with the silver-searcher ag
• (?:<pattern>): regex matches pattern but without generating a capture-group
• dpkg -S <file>: query package providing given file on debian-based systems
• dpkg -L <package>: list all files of an installed dpkg package
• echo lol|/usr/bin/cat /dev/stdin: use /dev/stdin as filename when the stdout from previous command schould be used. Useful for commands not supporting stdin as input source.
• vim <url>: open vim, download and show content of the given url
• tcpdump -i <interface> -pvn port 67 and port 68: see dhcp requests and responses for <interface>
• Adding a space before a bash command prevents it from being written to the history.
• date +"%s": show current time as unix timestamp
• date -d @<unix-timestamp>: convert unix timestamp into a human readable one
• ctrl+z and fg: suspend running applications via ctrl+z to get to the original shell and get back to the application via fg
• ffmpeg -i input.mp4 output.gif: Converts mp4 video into gif
• Send empty email to mailing list with -leave in front of the @ of the address: unsubscribe from mailing list, e.g. qemu-devel-leave@nongnu.org, see GNU Mailman FAQ
• systemctl list-units: List all registered units with their run state. Compact and easily grep-able

other til sites

• jvns.ca/til