will purge:

only installed apps: /^ii/!d

avoiding current kernel stuff: /'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d

using app names: s/^[^ ]* [^ ]* \([^ ]*\).*/\1/

avoiding stuff without a version number: /[0-9]/!d

This commands will make it easier to select only common items between two files being compared. If your lines start with things other than lowercase a-z, adjust this Regex appropriately. Number of lines in the output has been set to no more than 10000, and should be adjusted as needed.

Stuck behind a restrictive firewall at work, but really jonesing to putty home to your linux box for some colossal cave? Goodness knows I was...but the firewall at work blocked all outbound connections except for ports 80 and 443. (Those were wide open for outbound connections.) So now I putty over port 443 and have my linux box redirect it to port 22 (the SSH port) before it routes it internally. So, my specific command would be:

Note that I use -A to append this command to the end of the chain. You could replace that with -I to insert it at the beginning (or at a specific rulenum).

My linux box is running slackware, with a kernel from circa 2001. Hopefully the mechanics of iptables haven't changed since then. The command is untested under any other distros or less outdated kernels.

Of course, the command should be easy enough to adapt to whatever service on your linux box you're trying to reach by changing the numbers (and possibly changing tcp to udp, or whatever). Between putty and psftp, however, I'm good to go for hours of time-killing.

additionally use "find /etc/cron*" for cronscripts

Sometimes you're trying to read through an xml file to determine whats wrong with it and a tool had removed all the linebreaks. xmllint will go ahead and make it pretty for you.

imports a public key from the web. I know this by head.. but useful nevertheless

Appended to grub boot parameters ... gives shell ... password recovery

I had some trouble removing empty lines from a file (perhaps due to utf-8, as it's the source of all evil), \W did the trick eventually.

Starts midnightcommander and allows you to detach the console; use ctrl-\ to detach

Then at a later time you can reconnect using

In my experience dtach works much better for programs like irssi, mutt, mc, aptitude than screen does.

search the newest *.jpg in the directory an make a copy to newest.jpg. Just change the extension to search other files. This is usefull eg. if your webcam saves all pictures in a folder and you like the put the last one on your homepage. This works even in a directory with 10000 pictures.

Using the grep command, retrieve all lines from any log files in /var/log/ that have one of the problem states

This will create a 10 MB file named testfile.txt. Change the count parameter to change the size of the file.

As one commenter pointed out, yes /dev/random can be used, but the content doesn't matter if you just need a file of a specific size for testing purposes, which is why I used /dev/zero. The file size is what matters, not the content. It's 10 MB either way. "Random" just referred to "any file - content not specific"

Makes any files in the current directory (and any sub-directories) group-readable.

Using the "! -perm /g=r" limits the number of files to only those that do not already have this property

Using "+" on the end of the -exec body tells find to build the entire command by appending all matching files before execution, so invokes chmod once only, not once per file.

Makes it easy to add keys to new ppa sources entries in apt sources.list

Now to add the key for the chromium-daily ppa:

Useful if you have to put together multiple files into one and they are scattered across subdirectories. For example: You need to combine all .sql files into one .sql file that would be sent to DBAs as a batch script.

You do get a warning if you create a file by the same extension as the ones your searching for.

find . -type f -name *.sql -exec cat {} > BatchFile.txt \;

There are two ways to use "here documents" with bash to fill stdin:

The following example shows use with the "bc" command.

a) Using a delimiter at the end of data:

> k=1024

> m=k*k

> g=k*m

> g

> eeooff

1073741824

b) using the "inline" verion with three less-than symbols:

1073741824

One nice advantage of using the triple less-than version is that the command can easily be recalled

from command line history and re-executed.

PS: in this "description", I had to use the name "less-than" to represent the less-than symbol because the commandlinefu input text box seems to eat up the real less-than symbols. Odd.

You need sysstat and gawk for this to work.

This set of commands was very convenient for me when I was preparing some xml files for typesetting a book. I wanted to check what styles I had to prepare but coudn't remember all tags that I used. This one saved me from error-prone browsing of all my files. It should be also useful if one tries to process xml files with xsl, when using own xml application.

In the above example all files have 4 lines. In "file1" consecutive lines are: "num, 1, 2, 3", in "file2": "name, Jack, Jim, Frank" and in "file3": "scores, 1300, 1100, 980". This one liner can save considerate ammount of time when you're trying to process serious portions of data. "-d" option allows one to set series of characters to be used as separators between data originating from given files.

find all email addresses in a file, printing each match. Addresses do not have to be alone on a line etc. For example you can grab them from HTML-formatted emails or CSV files, etc. Use a combination of

to filter them.