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Big Countdown Clock in seconds
Requires figlet. Other than that, this should be portable enough across all the Bourne-compatible shells (sh, bash, ksh, zsh, etc). Produces a massive number using figlet that counts down the number of seconds for any given minute interval. For example, here's a 4-minute timer: $ i=$((4*60)); while [ $i -gt 0 ]; do clear; echo $i | figlet; sleep 1; i=$(($i-1)); done; And a 1-minute timer: $ i=$((1*60)); while [ $i -gt 0 ]; do clear; echo $i | figlet; sleep 1; i=$(($i-1)); done;

Simplest port scanner
Very handy way to perform a host scan if you don't have nmap,ncat,nc ...or other tools installed locally. When executing a command on a /dev/tcp/$host/$port pseudo-device file, Bash opens a TCP connection to the associated socket and UDP connection when using /dev/udp/$host/$port.A simlpe way to get servers banner is to run this command "cat < /dev/tcp/localhost/25" , here you will get mail server's banner. NOTE: Bash, as packaged for Debian, does not support using the /dev/tcp and /dev/udp pseudo-device it's not enabled by default Because bash in Debian is compiled with ?disable-net-redirections.

Empty Bind9 cache
Occasionally, to force zone updating, cache flush is necessary. The use of this command is better than restart the Bind9 process.

IFS - use entire lines in your for cycles
When you use a "for" construct, it cycles on every word. If you want to cycle on a line-by-line basis (and, well, you can't use xargs -n1 :D), you can set the IFS variable to .

view http traffic

Check whether laptop is running on battery or cable
If you want to do the same in OS X... grep as necessary for information you need....

Find the package that installed a command

Find files in multiple TAR files
A quick find command to identify all TAR files in a given path, extract a list of files contained within the tar, then search for a given string in the filelist. Returns to the user as a list of TAR files found (enclosed in []) followed by any matching files that exist in that archive. TAR can easily be swapped for JAR if required.

find the delete file ,which is in use

get rid of lines with non ascii characters
found here: https://stackoverflow.com/a/9035939


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