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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" }

Copy the full path of a file to the clipboard (requires xclip or similar)
Handy for those times you need to paste a file path in an IDE or some other app. sudo apt-get install xclip Then, for convenience, alias xclip to 'xclip -selection c' so you can just do something like realpath . | xclip

geoip lookup

check open ports without netstat or lsof

get all Google ipv4/6 subnets for a iptables firewall for example (updated version)
google has added 2 more netblocks...

Advanced python tracing
Trace python statement execution and syscalls invoked during that simultaneously

find all writable (by user) files in a directory tree (use 4 for readable, 1 for executable)

list block devices
Shows all block devices in a tree with descruptions of what they are.

peak amount of memory occupied by any process with "FOO" in its name
Show the maximum amount of memory that was needed by a process at any time. My use case: Having a long-running computation job on $BIG_COMPUTER and judging whether it will also run on $SMALL_COMPUTER.   http://man7.org/linux/man-pages/man5/proc.5.html VmHWM: Peak resident set size ("high water mark")

Substitute spaces in filename with underscore
Substitute spaces in filename with underscore, it work on the first space encountered.


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