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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" }

Know which modules are loaded on an Apache server
This let you know which modules has loaded the Apache server, very useful to know if the mod_rewrite is ready to use.

Print just line 4 from a textfile
this method should be the fastest

Google URL shortener
Shorter and made into a function.

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Watch and cat the last file to enter a directory
Great for watching things like Maildir's or any other queue directory.

Calculate sum of N numbers (Thanks to flatcap)
replaces "\n" with "+"

Watch the progress of 'dd'
Running this code will execute dd in the background, and you'll grab the process ID with '$!' and assign it to the 'pid' variable. Now, you can watch the progress with the following: $ while true; do kill -USR1 $pid && sleep 1 && clear; done The important thing to grasp here isn't the filename or location of your input or output, or even the block size for that matter, but the fact that you can keep an eye on 'dd' as it's running to see where you are at during its execution.

Count to 65535 in binary (for no apparent reason)
Yes, it's useless.

Bash logger


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