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Recall “N”th command from your BASH history without executing it.

display ip address
add this alias in .bashrc to fast check the ip address of your modem router alias myip="curl -s http://myip.dk | grep '' | sed -e 's/]*>//g'"

move you up one directory quickly
Alias a single character 'b' to move to parent directory. Put it into your .bashrc or .profile file. Using "cd .." is one of the most repetitive sequence of characters you'll in the command line. Bring it down to two keys 'b' and 'enter'. It stands for "back" Also useful to have multiple: alias b='cd ../' alias bb='cd ../../' alias bbb='cd ../../../' alias bbbb='cd ../../../../'

Mac OS X - List all of my machine's IP addresses
On the Mac, the format ifconfig puts out is little different from Linux: the IP address is space separated, instead of colon. That makes parsing the IP address easier. See releated command for Linux/Unix: http://www.commandlinefu.com/commands/view/651/getting-the-ip-address-of-eth0

Increase mplayer maximum volume
use '0' and '9' to increase/decrease volume. this is useful on laptops with low speaker volume.

Robust expansion (i.e. crash) of bash variables with a typo
By default bash expands an unbound variable to an empty string. This can be dangerous, if a critical variable name (a path prefix for example) has a typo. The -u option causes bash to treat this as an error, and the -e option causes it to exit in case of an error. These two together will make your scripts a lot safer against typos. The default behaviour can be explicitly requested using the ${NAME:-} syntax. A (less explicit) variation: #!/bin/bash -eu

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" }

add static arp entry to default gateway, arp poison protection

list current processes writing to hard drive

Cleanly manage tempfiles in scripts
Cleanly create tempfiles using mktemp and remove them using traps instead of removing them in the end of the script. This way, you make sure the tempfiles are removed properly even if the script is killed or interrupted. For a user script in KDE4, you can set TMPROOT using : $ TMPROOT=$(kde4-config --path tmp)


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