LINUX NEWS
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Thursday, October 11, 2001TABLE OF CONTENTS
1) Sean’s Notes
2) Linux News
Aussies say GPL is OK
Interview with Linus
Kernel 2.4.11 Released
StarOffice offers IT real choice3) Linux Resources
Encrypted Filesystem Lab Notes
Opportunistic Encryption
PGP or GPG?
LPI Crash Course
Read and Write Excel Files in Perl4) App o’ the week
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1) Sean’s Notes
In previous articles I’ve used regular expressions to perform various tasks. You may remember them as a string of punctuation that doesn’t make any sense, but I hope that after this week, you’ll be able to use them in your work with Linux.
A regular expression is nothing more than a pattern to be matched. They’re used everywhere, from “awk” to “zegrep”, and luckily are fairly consistent. They can be simple or complex, it’s up to you.
You’ve probably used a regular expression before without even knowing it:
$ ps -ef | egrep sendmail
can be used to see if sendmail is running. In this case, “sendmail” is the regexp, and is the simplest form of all, matching the string “sendmail” itself. Thus, the following will match…
sendmail aaaasendmailzzzz
…but the following will not:
Sendmail send mail banana
In the first case, “sendmail” by itself matches the given string of “sendmail”. The second string contains “sendmail” within it, still valid. However, being very literal, “Sendmail” with a capital ‘S’ does not equal “sendmail”, nor does “send mail” (space). Of course, banana isn’t even close.
Now, suppose you wanted to match “sendmail”, with or without a capital ‘S’. We could construct two separate commands, each with one variation, or we could make use of square brackets : []. Square brackets mean “one of the characters inside is OK”:
$ ps -ef | egrep ‘[sS]endmail’
This time, I protected our string with quotes because some shells might start interpreting the special characters. Looking at the regexp, it will match a string that starts with either ‘s’ or ‘S’, followed by “endmail”.
What if we’re looking for a string, but are not sure of a letter? For example, you’re doing a crossword puzzle, and need a five letter word that starts with “tr”, and ends with “ck”. In this case, the period has meaning in that it matches any single character:
$ egrep ‘tr.ck’ /usr/dict/words
If you run that command, you’ll probably get a whole list of words, because egrep will look for substring matches if we don’t tell it otherwise.
To fix this one up, the ^ and $ characters are employed. ^ matches the beginning of a line, and $ the end of a line. Since /usr/dict/words has one word per line, we can use:
$ egrep ‘^tr.ck$’ /usr/dict/words
which means “find a line that begins with tr, has any character followed by ck”. My search returned:
track trick truck
Two more characters will really demonstrate the power of regular expressions: * and +. * means “zero or more of the previous”, while + means “one or more of the previous”
The regexp ‘hi*’ will match “h”, “hi”, “hii” and so on, but ‘hi+’ will match only the latter two because of the requirement for one i. + and * may be combined with other operators, such as .*, which means “anything”.
Let’s say you were trying to find the spelling of “acquiescent” out of /usr/dict/words. You knew it ends with ent, so we’ll craft our regexp starting there:
$ egrep ‘ent$’ /usr/dict/words
457 words on my machine, so we’ll have to be a bit more specific.
Knowing it starts with “a” doesn’t help a lot, only bringing it down to 71.
$ egrep ‘^a.+ent$’ /usr/dict/words
I know it’s got a q in there, but is it “acq” or “aq”?
$ egrep ‘^ac?q.+ent$’ /usr/dict/words acquiescent
Our final regexp refers to a string that begins with a, may have a c, then has a q followed by an indeterminate number of letters, but ending in ent.
One final aspect of regexps I’ll explain today is similar to the square brackets, but refer to strings. To check on the status of nfs, I want to make sure nfsd, portmap and rpc.mountd are running. I could run…
$ ps -ef | egrep nfsd $ ps -ef | egrep mountd $ ps -ef | egrep portmap
…but I’d rather run them as one command. Parenthesis () and the | “or” operator mean that multiple strings can match:
$ ps -ef | egrep ‘(nfsd|mountd|portmap)’
will match any line that has either of the strings “nfsd” or “mountd” (or both, for that matter).
Before I sign off, a common trick in shell scripts uses the [] operators to correct a common flaw. When I type:
$ ps -ef | egrep sendmail
I end up with:
…… sendmail: accepting connections …… egrep sendmail
What’s that “egrep sendmail” doing in there? According to Unix, it’s to pump the output of ps -ef into the input of egrep. In order to do so, it has to create the egrep process, which contains the “sendmail” string. To prevent this,
$ ps -ef | egrep ‘[s]endmail’
As we learned above, the [] operator means “anything inside”, which can only be an ‘s’ in this case. “sendmail” does not match “[s]endmail” (which is how would appear in the process entry for egrep), so only bona fide sendmail processes are shown.
So that’s regexp in a nutshell. There are a lot more operators, especially once you get into the perl implementation of it. However, a basic understanding of regexps will help you in your shell scripting, not to mention shaving off a lot of keystrokes when doing your regular work.
Long live the Penguin,
Sean swalberg@cramsession.com
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2) Linux News
Aussies say GPL is OK
This report looks at the validity of Craig Mundie’s “GPL is Evil” speeches from an Australian standpoint. I’m sure you won’t be surprised at the results, but it’s still a good read.
http://australianit.news.com.au/articles/0,7204,2774764%5E15306%5E% 5Enbv%5E,00.html
Interview with Linus
Interviews with Linus are usually pretty good reading. In this one, he talks a bit about what’s on tap for 2.5/2.6, and gives his take on the “GNU/Linux” vs “Linux” naming debate. His answer to the latter question is always good for a chuckle; this time is no exception.
http://www.osnews.com/story.php?news_id1
Kernel 2.4.11 Released
Once again, we’ve got a new kernel. Nothing too exciting, just a lot of driver fixes. An interesting note in the ChangeLog about a fix for x86 boxes with more than 8 CPUs, so if you’re in that lucky few, this one will be of special interest.
http://www.kernel.org/pub/linux/kernel/v2.4/ChangeLog-2.4.11
StarOffice offers IT real choice
As I mentioned last week, StarOffice 6.0 beta was released, and already I’m happy with it. It would appear that ZDNet is also looking at it in a favourable light, even making comparisons to Word. If you haven’t had the chance to try out StarOffice, give this article a read, then follow the links to download a free office suite.
http://www.zdnet.com/products/stories/reviews/0,4161,2816213,00.htm l
3) Linux Resources
Encrypted Filesystem Lab Notes
With the modular nature of Unix, adding a layer of encryption on top of your filesystem isn’t very hard. This set of notes should be able to guide you through the process of keeping your data protected.
http://www.zen-data.com/labnotes/lab002.html
Opportunistic Encryption
One of the original goals of the Free S/WAN project was to create an implementation of IPSEC that can build tunnels on demand, such that users don’t even know their traffic is protected. This summer, the goal was achieved in part, and this document explains how to set up this very important feature.
http://www.freeswan.org/freeswan_trees/freeswan-1.91/doc/opportunis m.howto
PGP or GPG?
I’ve been a longtime user of PGP to secure my email, but recently I’ve been meaning to make the switch to the Free implementation, GPG. Since most of my friends use PGP, I knew I’d run into some trouble, but luckily, this document helped set me straight.
http://technocage.com/~caskey/gnupg/pgp2gnupg.html
LPI Crash Course
For those of you looking to challenge the LPI Linux certification, O’Reilly has kindly made available a crash course in the topic. Reading through, it’s just as valid for other Linux certifications, so keep this one handy when you’re studying.
http://linux.oreilly.com/news/lpilinux_0601.html
Read and Write Excel Files in Perl
Spreadsheet::WriteExcel and Spreadsheet::ParseExcel are two Perl modules that allow you to read and write Excel files from within Perl. This article explains the modules themselves, and how to use them.
http://www-106.ibm.com/developerworks/linux/library/l-pexcel/
4) App o’ the week
RADIUS is a common service to offer to keep track of users and privileges. Routers and access servers can query a central server, which greatly increases management. The FreeRADIUS project is an improvement on the traditional Livingstone RADIUS server, but with a whole whack of features not seen in other implementations.
http://www.freeradius.org/
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