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Determine space taken by files of certain type
Just how much space are those zillions of database logs taking up ? How much will you gain on a compression rate of say 80% ? This little line gives you a good start for your calculations.

set prompt and terminal title to display hostname, user ID and pwd
used in an if-then-else in case the default shell is ksh, not bash. The $(basename ${0#-}) is handy to echo which shell and strip the dash some flavors put in front of "bash" if [ $(basename ${0#-}) == "bash" ] ; then export PS1='\[\e]0;\h \u \w\a\]\n\[\e[0;34m\]\u@\h \[\e[33m\]\w\[\e[0;32m\]\n\$ ' else HOST=`hostname` ESC=`echo "\033"` BEL=`echo "\007"` RAW=`echo "\r"` export PS1='-${RAW}${ESC}]0;${HOST} ${USER}${BEL}-${ESC}[0;34m${USER}${ESC}[0m@${ESC}[0;34m${HOST%%.*}${ESC}[0;33m${ESC}[0m $ ' fi

find filenames and directory names that doesn't conform ISO 9660 level 2
You might want to check what file and directory names would be renamed or chopped if you create iso 9660 level 2 image out of them. Use this command to check first.

Calculate days on which Friday the 13th occurs (inspired from the work of the user justsomeguy)
Friday is the 5th day of the week, monday is the 1st. Output may be affected by locale.

list processes with established tcp connections (without netstat)
Uses lsof to list open network connections (file descriptors), grepping for only those in an established state

Display the standard deviation of a column of numbers with awk
This will calculate a running standard deviation in one pass and should never have the possibility for overflow that can happen with other implementations. I suppose there is a potential for underflow in the corner case where the deltas are small or the values themselves are small.

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" }

Check if you need to run LaTeX to update the TOC
To check if the table-of-content in a LaTeX document is up-to-date, copy it to a backup before running LaTeX and compare the new .toc to the backup. If they are identical, it is updated. If not, you need to run LaTeX again.

Checks apache's access_log file, strips the search queries and shoves them up your e-mail
as unixmonkey7109 pointed out, first awk parse replaces three steps.

Format date/time string for a different day
The "date' command has options to easily format the date, day, month, time, etc. But what if you want a relative date or time. Like, I wanted yesterday's date in a particular format. You may want the exact date of "2 months ago" or "-3 days" nicely formatted. For that, you can use this command. The --date option takes fuzzy parameters like the ones mentioned in the previous sentence.


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