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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" }

Download all Phrack .tar.gzs

Show a Package Version on Debian based distribution
if you don't want to show string "version?, then use awk or cut filter it: apt-cache show pkgname | grep -i "version:" | awk '{ print $2 }' we can also use regex to search many packages and show their versions: apt-cache search pkgregex | grep -i "version:"

Count Files in a Directory with Wildcards.
If the dir | wc -l Command not working.

Is today the last day of the month?
Nice simple example of something we can do in bash.

Mount the first NTFS partition inside a VDI file (VirtualBox Disk Image)
Found at: http://forums.virtualbox.org/viewtopic.php?t=52

Create a square thumbnail or favicon using ImageMagick
Resize `file.png` to a 32x32 px image. Use a value other than 32 to create other icon sizes (e.g. 16x16 or 32x32). Combine two favicon sizes using: `convert icon-16px.png icon-32px.png favicon.ico` For a social media preview image, use `2:1#` for the extent and `1200` for the scale.

Backup with versioning
Apart from an exact copy of your recent contents, also keep all earlier versions of files and folders that were modified or deleted. Inspired by EVACopy http://evacopy.sourceforge.net

Add temporary swap space
In addition to a swap partition, Linux can also use a swap file. Some programs, like g++, can use huge amounts of virtual memory, requiring the temporary creation of extra space.

Check SSH public and private keys matching
Tested in bash4


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