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find an unused unprivileged TCP port
perl-less way

Compression formats Benchmark
See: http://imgur.com/JgjK2.png for example. Do some serious benchmarking from the commandline. This will write to a file with the time it took to compress n bytes to the file (increasing by 1). Run: $ gnuplot -persist

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" }

Line Separator That is Width of Terminal
Creates a line seperator that will be the width of your window.

Compare copies of a file with md5
I had the problem that the Md5 Sum of a file changed after copying it to my external disk. This unhandy command helped me to fix the problem.

Search some text from all files inside a directory

Squish repeated delimiters into one
This can be particularly useful used in conjunction with a following cut command like $echo "hello::::there" | tr -s ':' | cut -d':' -f2 which prints 'there'. Much easier that guessing at -f values for cut. I know 'tr -s' is used in lots of commands here already but I just figured out the -s flag and thought it deserved to be highlighted :)

Find files and calculate size of result in shell
Find files and calculate size with stat of result in shell

Get information about libraries currently installed on a system.
This command is very helpful when we need to duplicate a test scenario and first we want to find out the installed libraries together with the version and release numbers and architecture. (look example) Command can be tuned by choosing just the names of libraries we are interested in. For example glibc and gcc.

Binary search/replace
Replace all instances of "A" with "B" in file "source" saved as file "destination". !! IF A/B is multi-byte, then separate bytes with spaces like so: "s/20\ 0A/00/g".


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