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Aptitude pattern match
Could be dangerous, if you have many packages all beginning with 'foo' or 'bar'. This will easily remove them all from your system.

View a colorful logfile using less

Rename all files which contain the sub-string 'foo', replacing it with 'bar'
That is an alternative to command 8368. Command 8368 is EXTREMELY NOT clever. 1) Will break also for files with spaces AND new lines in them AND for an empty expansion of the glob '*' 2) For making such a simple task it uses two pipes, thus forking. 3) xargs(1) is dangerous (broken) when processing filenames that are not NUL-terminated. 4) ls shows you a representation of files. They are NOT file names (for simple names, they mostly happen to be equivalent). Do NOT try to parse it. Why? see this :http://mywiki.wooledge.org/ParsingLs Recursive version: $ find . -depth -name "*foo*" -exec bash -c 'for f; do base=${f##*/}; mv -- "$f" "${f%/*}/${base//foo/bar}"; done' _ {} +

GRUB2: Set Imperial Death March as startup tune
Kudos to http://www.commandlinefu.com/commands/view/8275/grub2-set-super-mario-as-startup-tune

online MAC address lookup

Safely remove old unused kernels in Ubuntu/Debian
Removes piling kernels from /boot, save the current one. This command DOES NOT remove the 'linux-image-generic' package, so you'll continue getting kernel updates

list block devices
Shows all block devices in a tree with descruptions of what they are.

Perform a branching conditional
This will perform one of two blocks of code, depending on the condition of the first. Essentially is a bash terniary operator. To tell if a machine is up: $ ping -c1 machine { echo succes;} || { echo failed; } Because of the bash { } block operators, you can have multiple commands $ ping -c1 machine && { echo success;log-timestamp.sh }|| { echo failed; email-admin.sh; } Tips: Remember, the { } operators are treated by bash as a reserved word: as such, they need a space on either side. If you have a command that can fail at the end of the true block, consider ending said block with 'false' to prevent accidental execution

Clean up display when the bash prompt is displayed
This will cause bash to fix a garbled terminal before the prompt is printed. For example, if you cat a file with nonprintable character sequences, the terminal sometimes ends up in a mode where it only prints line drawing characters. This sequence will return the terminal to the standard character set after every command.

Drop or block attackers IP with null routes
Someone might attack on your system. You can drop attacker IP using IPtables. However, you can use route command to null route unwanted traffic. A null route (also called as blackhole route) is a network route or kernel routing table entry that goes nowhere. Matching packets are dropped (ignored) rather than forwarded, acting as a kind of very limited firewall. The act of using null routes is often called blackhole filtering.


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