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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" }

Extract public key from private
This will extract the public key that is stored in the private key using openssl.

Unix commandline history substitution like ^foo^bar BUT for multiple replacements
#1 You invoked a command chain. #2 You globaly replace the scriptnames and execute them direct #3 The new executed command chain [# ^foo^bar] would only replace the firts match [foo] with [bar].

Webcam view with vlc
Quick command to test your webcam. Press 'f' to toggle fullscreen. Can also use 'vlc v4l2://' if you want gui controls. For higher/smoother framerate lower the default resolution: $ cvlc v4l2:// :v4l2-width=320 :v4l2-height=240 &

Set gnome wallpaper to a random jpg from the specified directory
Every time this is run it will change your background picture. For added fun Add some DBUS magic: . $HOME/.dbus/session-bus/`cat /var/lib/dbus/machine-id`-0 export DBUS_SESSION_BUS_ADDRESS and a crontab entry: */5 * * * * above_command_in_script.sh >/dev/null 2>/dev/null now wallpaper changes every 5 mins

Replaces a color in a PDF document, useful for removing a dark background before printing.
The pdf is first converted to a bitmap, so change "-density" to match your printer resolution. Also be careful about the RAM required. In this example rgb(0,0,0) is replaced by rgb(255,255,255), change to suit your needs.

Create a continuous digital clock in Linux terminal
Same effect, only shell commands.

Get the gravatar UTL for a given email address

Print a row of characters across the terminal
Pure Bash This will print a row of characters the width of the screen without using any external executables. In some cases, COLUMNS may not be set. Here is an alternative that uses tput to generate a default if that's the case. And it still avoids using tr. $ printf -v row "%${COLUMNS:-$(tput cols)}s"; echo ${row// /#} The only disadvantage to either one is that they create a variable.

Find duplicate UID in /etc/passwd
You can use only awk


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