Commands by mplf (1)

What's this? is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

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Convert seconds to [DD:][HH:]MM:SS
Converts any number of seconds into days, hours, minutes and seconds. sec2dhms() { declare -i SS="$1" D=$(( SS / 86400 )) H=$(( SS % 86400 / 3600 )) M=$(( SS % 3600 / 60 )) S=$(( SS % 60 )) [ "$D" -gt 0 ] && echo -n "${D}:" [ "$H" -gt 0 ] && printf "%02g:" "$H" printf "%02g:%02g\n" "$M" "$S" }

intercept stdout/stderr of another process
similar to the previous command, but with more friendly output (tested on linux)

Watch contents of a file grow
In this case, I'm keeping an eye on /var/log/messages, but of course any file will do. When I'm following a file, I generally don't want to see anything other than what has been added due to the command or service I've executed. This keeps everything clean and tidy for troubleshooting.

Realtime lines per second in a log file
Displays the realtime line output rate of a logfile. -l tels pv to count lines -i to refresh every 10 seconds -l option is not in old versions of pv. If the remote system has an old pv version: ssh tail -f /var/log/apache2/access.log | pv -l -i10 -r >/dev/null

Validate date, also a date within a leap year
Important to know: a valid date will return 0, otherwise 1!

Stripping ^M at end of each line for files
That "^M" is Ctrl-M, which is a carriage return, and is not needed in Unix file systems. Where ^V is actually Ctrl-V and ^M is actually Ctrl-M (you must type these yourself, don't just copy and paste this command). ^V will not be displayed on your screen.

list files recursively by size

Help shell find freshly installed applications (re: PATH)
Immediately after installing things into your PATH (e.g. under /usr/bin), currently open shells cannot find them ("zsh: command not found"). Use rehash to get the shell to rescan available executables.

Output files without comments or empty lines
Filter comments and empty lines in files. I find this very useful when trying to find what values are actually set in a very long example config file. I often set an alias for it, like : alias nocomment='grep -v "^\($\|#\)"'

Grab IP address on machine with multiple interfaces
Instead of hard-coding in a check to scrape info from ifconfig based on a specific interface, do it in a more portable way. This works really well if you switch between wired, wireless, bluetooth or even VPN connections. You can get your current IP in a script (since it'll be something like tun0 instead of eth0 or wlan1). This uses a well known public ip address, but it doesn't actually connect to it, it just shows you the route it would take.

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