Frank

Skype under investigation for NSA links

According to today’s Guardian, Skype is being tackled by the data protection commissioner in Luxembourg over concerns it has secret links with the US National Security Agency, and its Prism communications intercept programme. Like many “interesting” companies such as eBay, Amazon and even Starbucks, Skype chose to be be based in the Luxembourg in the hope it would be left alone. However, the infamous tax haven’s constitutionally enshrined right to privacy might turn around and bite Skype.

Microsoft bought Skype a couple of years ago; it had once been owned by eBay and, as a separate division, Microsoft has presumably decided to keep it in Luxembourg for the tax advantages. However, while Microsoft was allegedly one of the first large technology group to be pulled in to Prism, Skype has been widely thought of as a secure communications channel. If Luxembourg-based Skype has been passing intercepts to the NSA, its users and the local authorities will not be pleased.

I understand that the local law does allow this kind of thing, and for it to remain secret, if it’s specially negotiated by the government. And as such the data commissioner may not have been in the loop.

But, you may wonder, how does an encrypted peer-to-peer system like Skype get intercepted anyway? The protocol was designed to pirate media files in such a way that lawful authorities were unable to track or disrupt it (which is why no network administrators would ever want it on their LANs). If it has weaknesses, they must have been there from the start. And I believe they were.

A few years back I was talking to someone from Facetime, a manufacturer of firewalls. They’ve since found that flogging their domain to Apple for an iPhone product is also lucrative, and now they’re called Actiance. But I digress.

Facetime had struck a deal with eBay to get details of the secret protocol so that they could manage Skype on local networks. As it’s obfuscated and designed to avoid firewalls, this is a neat trick, and they were the only people able to do it at the time. As an example, they were able to determine which versions of Skype were in use and block those that didn’t fit with company policy. In other words, they could positively recognise the obfuscated protocol and make sense of it.

According to the files the Guardian claims to have seen, Skype was ordered to cooperate with the NSA in February 2011, and it only took them a few months to have call intercepts in place. I’m not that surprised; given the Facetime firewall’s abilities I suspected that payload decryption was going to be possible if you asked the right questions whilst brandishing a big enough stick.

Making this information public, as is now the case, is simply going to push the people that should be intercepted on to systems not under the influence of the USA. How about a Chinese Skype-alike instead? Perhaps not, as it’s widely believed that the Chinese version has a back-door for the local authorities to plunder. But there are plenty of anarchist outfits out there with the ability to write a VoIP system that isn’t compromised by big business’s need to cooperate with governments if they want to make a profit.

Meanwhile, let’s see how Luxemburg’s data protection commissioner gets on.

9-October-139-October-13

Spam from global switch

My spam traps pick up dodgy emails from all sorts, including large companies that ought to know better. But today one was hit with a marketing communication from Global Switch. Not from an errant client of the data centre, but from Global Switch themselves, marketing their rack space (half price for the first 12 months, apparently).

I’m not sure what to make of this, but if you’re thinking of starting up a spamming operation, Global Switch looks like the place to be. If they don’t care whether they’re using legitimate, opt-in lists, why should they hassle their customers. Needless to say I contacted them about it; needless to say there was no one available to comment. If anyone from Global Switch is out there, it’s still not too late.

Further:

I did get through to Global’s sales team. While they stopped short of condemning the practice, they said they’d investigate if I gave them enough information to identify the honeypot. I’m sure they’d wouldn’t have bought the list they used if they suspected it was dodgy, which just goes to show.

3-October-13

Who needs a botnet when you can Yahoo?

Someone, somewhere is making full use of Yahoo webmail to send out what could be millions of fake emails pretending to be Amazon order confirmations (extrapolating on the numbers received here). Needless to say, they really contain a ZIP file with a rather nasty looking Microsoft executable file inside.

My guess is they’re using accounts compromised earlier in the year, as reported here, which gets them through spam filters as most ISPs trust Yahoo. Actually, ISPs generally don’t trust Yahoo but their users don’t see it that way when their friends’ Yahoo email is blocked.

Is this Yahoo’s fault? Normally I’d blame the criminals, but in this case Yahoo could be doing a lot more to to help. This has been going on for three days, and there’s no legitimate reason why any of its users should be sending out with addresses @amazon.co.uk. Even if they can’t scan to detect the latest malware, recognising these fake emails is easy enough.

It’s hardly a new tactic by the criminals, of course. amazon.co.uk’s name was abused back in May to deliver similar Trojan malware.

It’s about time Yahoo (and other freemail services) took responsibility for the damage caused by their business model.

27-August-1328-August-13

Chauvet Obey 40 blacks out when you change fixture

I needed to test some DMX controlled lighting figures recently, and after looking around I decided to get an Chauvet Obey 40 controller. It’s not the cheapest, but it won’t break the bank, and it supports more channels than the entry level models – and does scenes and sequences (chases).

The design looks fairly straightforward. If you want simply use it to control light fixtures manually you need only press the button for the fixture in question on the left and then use the faders corresponding to the channels you want to adjust until you get just the right shade of puce. You can toggle multiple fixtures on and off, and control them in batches. So far so good.

Having got this set up, I was horrified to discover that when you de-select a fixture the Obey 40 turns it off! This means you can’t go through adjusting all your lights in turn. Apparently the unit was designed to work in programmed mode, where you set up scenes and sequences of scenes and cycle through them. It can do that, okay. If that’s all you want.

After tearing my hair out for several hours I discovered, by accident, that if you press the Auto/Del button to toggle the “Auto Trigger” light on the LED display to “on”, the desk works the way you might hope – select the fixture(s) you want, adjust it and then select another fixture. This is, apparently, the “Auto Bank Playback” mode, which suggests it may not work so well if you have things programmed in a bank but this hardly seems to matter for manual control. Just make sure it’s sequencing through an empty bank.

This appears to be an undocumented feature, and was news to the helpful people at Chauvet in Nottingham. I get the feeling this was something that irritated them about the design, too.

So – if you’re stuck in the same position, trying to get manual control, the non-intuitive answer is to turn it in to “auto” mode. My unit was manufactured in April 2013; this may not apply to other units, which may have different firmware.

Additional: If you don’t mind the “programming” light blinking away like mad, you can also control it manually in programming mode – just don’t bother saving the scene.

3-August-134-August-13

Your Smart TV is watching YOU

There were a couple of interesting presentations at Black Hat yesterday Aaron Grattafiori and Josh Yavor from iSEC Partners and Seungjin Lee from Korea University were both talking about hijacking Smart TVs. These devices are Internet connected and basically do a lot of their stuff using web browser technology, including JavaScript and other well known attack vectors. iSEC Partners were testing Samsung TVs in particular, but they all work pretty much the same way and apparently the manufacturers’ programmers haven’t done much to consider the security aspects.

Grattafiori was particularly keen to point out that the cameras on such devices were as susceptible to hijacking as anything else.

He went on “Because the TV only has a single user, any type of compromise into an application or into Smart Hub, which is the operating system — the smarts of the TV — has the same permission as every user, which is, you can do everything and anything.”

He suggested you might want to make sure the TV in your bedroom has it’s lens covered with a sticky label.

Earlier this year Samsung has issued a software update for the TVs affected by the security flaws described in Las Vegas, but the fact they’re all using flaky browser technology means we should all be wary of them.

31-July-1311-August-13

Mark Shuttleworth’s Ubuntu Edge Dream

Mark Shuttleworth’s software company, Canonical Ltd, trying to raise $32M to build the first 40,000 units of a smart-phone type device that can run Ubuntu Linux. I predict he’s raise the money, and make the handsets. But the idea will tank anyway. Here’s why.

The concept of a ‘phone capable of running a desktop OS is easy to understand. When you want to use the desktop Ubuntu side you plug it in to a real monitor and keyboard – say one at home and one in the office. When you’re on the move it will run Android Linux (for Android is simply Linux with an Android graphical shell). You carry your environment with you, and carry on working wherever you are, assuming you have a monitor and keyboard available. If you run the Ubuntu graphical environment on the move, using the handset’s touch-screen it’s going to be pretty painful.

People investing about £600 will get a ‘phone, if they’re ever made. Is this an investment, or a pre-ordering deal? I think it’s up to you whether you invest enough to get a ‘phone, or buy even more equity as an investment in the future of the device, but I suspect a lot of people will simply be after the latest gadget. Whether £600 is too much for the Penguinistas, remains to be seen.

I think they stand a good chance of raising the money because they’re selling a dream that’s been around in various forms since the dawn of personal computing. One of the early incarnations would be the Apple IIc, which looked a bit like a portable typewriter when cut free from its monitor. With it you could carry your computer back from the office, but it didn’t catch on. Then, came the Tandon Data Pac, a hard disk cartridge. With a cartridge slot in PCs at the locations you needed to work, you could carry the important part of your environment with you. In those days, Microsoft didn’t do anything prevent hard disk transplants, so this was a realistic idea. But it didn’t catch on. Whether there are 40,000 people in the world who still have this dream is a good question.

Now we have laptop/notebook/netbook PCs, which are easy enough to carry in a briefcase if you get the right kind. I have always had the right kind, starting with the Cambridge Z88, moving on to the Sony Vaio and currently the Lenovo S10-3. At around 1Kg, they’re truly portable but although the Lenovo is modern, it was only on the market for a year or two as the 10″ screens format isn’t for well received by the masses. They demands big and fast, and they aren’t really worried about the battery life as long as they look cool. People often ask me “where can I get one of those”, and I tell them. (Currently only Asus and Acer producing a highly portable laptop/netbook). The snag is that when they get one they then “must” run Office 365, or some similar bloatware that a small CPU can’t handle fast.

If you don’t need battery life and the ability to work on the move, but simply want to carry your PC to and from the office, there are small form factor machines also from ASUS and Acer. If you want really small there’s the Fit-PC2 which can actually fit in a pocket. I must admit, I bought one because I thought it was a neat design. These are all Intel based and can run unmodified Windows, and yet they haven’t really caught on either. The Ubuntu Edge will not run Windows; it runs Linux. This means it won’t run Microsoft Office, ever. My experience has shown this is a big problem for a lot of people. There’s nothing wrong with OpenOffice; it’ll work with Microsoft Office files and vice versa. It’s free, whereas Microsoft Office costs and small fortune. Yet in nearly every case, people who I’ve set up with OpenOffice for cost reasons have hankered after the Microsoft version, and most have gone out and bought it (or otherwise acquired it) within a year.

The CPU for the Ubuntu Edge has yet to be announced, but based on size, battery life and heat dissipation it’s very unlikely to be Intel, or even Intel compatible. The only thing that will fit will be RISC, and given the binary nature of Linux distributions it’ll be the second-best choice of ARM. Or will its users be expected to compile everything from source? No. It’ll be an ARM and the models that are capable of running Linux with a GUI at nearly the right speed will still rip through the battery at an alarming rate.

The final nail in its coffin will be the way people currently commute with their computing environment. This comes down to cheap and cheerful thumb drive, if you can find a ubiquitous Windose PC at both ends, or on-line applications such as Google Docs if you’re really serious about it; all your data and applications on every web browser, and impossible to lose at that. If you can find a keyboard and monitor at both ends, you’re probably going to find a web browser anyway so why bother to carrying your stuff on a mobile ‘phone instead? It’s a solution to a problem that has been a “difficult sell” for 30 years, and which has now been solved by the Internet. Okay, this allows you to use an Android ‘phone between PCs, but you could just get an Android ‘phone to plug that gap in your life.

28-July-1328-July-13

Email addresses used by comment spammers on WordPress

On studying the behaviour of comment spammers I became interested in the email addresses they used. Were they genuine and where were they from? Well of course they’re not likely to be genuine, but it is possible to force them to register with an address if they want their comments to appear – even if they don’t. Here’s what I found:

When the spammers were required to register, these are the domain names they registered with:

Domain	Percent
hotmail.com	25%
mailnesia.com	19%
Others (unique)	16%
gmail.com	7%
o2.pl	7%
outlook.com	5%
emailgratis.info	4%
gmx.com	2%
poczta.pl	2%
yahoo.com	2%
more-infos-about.com	1%
aol.com	1%
go2.pl	1%
katomcoupon.com	1%
tlen.pl	1%
acity.pl	1%
dispostable.com	1%
live.com	1%
mail.ru	1%
se.vot.pl	1%
acoustirack.com	<1%
butala.htsail.pl	<1%
cibags.com	<1%
eiss.xoxi.pl	<1%
justmailservice.info	<1%
laposte.net	<1%
pimpmystic.com	<1%
twojewlasnem.pl	<1%
wp.pl	<1%

Where the authenticity of the address is more questionable, although the sample a lot larger, the figures are as follows:

Domain	Percent
gmail.com	40%
yahoo.com	11%
Other (unique)	6%
hotmail.com	6%
aol.com	4%
ymail.com	2%
googlemail.com	2%
gawab.com	2%
bigstring.com	1%
zoho.com	1%
t-online.de	1%
inbox.com	1%
web.de	1%
yahoo.de	1%
arcor.de	1%
live.com	1%
freenet.de	1%
yahoo.co.uk	1%
comcast.net	1%
mail.com	1%
gmx.net	1%
gmx.de	1%
outlook.com	<1%
live.cn	<1%
hotmail.de	<1%
msn.com	<1%
livecam.edu	<1%
google.com	<1%
live.de	<1%
rocketmail.com	<1%
gmail.ocm	<1%
wildmail.com	<1%
moose-mail.com	<1%
hotmail.co.uk	<1%
care2.com	<1%
certify4sure.com	<1%
snail-mail.net	<1%
1701host.com	<1%
cwcom.net	<1%
maill1.com	<1%
wtchorn.com	<1%
chinaadv.com	<1%
noramedya.com	<1%
o2.pl	<1%
vegemail.com	<1%
vp.pl	<1%
24hrsofsales.com	<1%
kitapsec.com	<1%
peacemail.com	<1%
whale-mail.com	<1%
wp.pl	<1%
aim.com	<1%
animail.net	<1%
bellsouth.net	<1%
blogs.com	<1%
email.it	<1%
mailcatch.com	<1%
rady24.waw.pl	<1%
titmail.com	<1%
fastemail.us	<1%
btinternet.com	<1%
harvard.edu	<1%
onet.pl	<1%
yahoo (various international)	<1%
akogoto.org	<1%
concorde.edu	<1%
freenet.com	<1%
leczycanie.pl	<1%
mail15.com	<1%
speakeasy.net	<1%
yale.edu	<1%
123inholland.co.nl	<1%
SolicitorsWorld.com	<1%
apemail.com	<1%
buysellonline.in	<1%
email.com	<1%
help.com	<1%
ipad2me.com	<1%
ismailaga.org.tr	<1%
live.fr	<1%
myfastmail.com	<1%
mymail.com	<1%
ngn.si	<1%
redpaintclub.co.uk	<1%
stonewall42.plus.com	<1%
traffic.seo	<1%
xt.net.pl	<1%
a0h.net	<1%
accountant.com	<1%
alphanewsroom.com	<1%
att.net	<1%
auctioneer.com	<1%
brandupl.com	<1%
canplay.info	<1%
charter.net	<1%
cluemail.com	<1%
darkcloudpromotion.com	<1%
earthlink.com	<1%
earthlink.net	<1%
eeemail.pl	<1%
emailuser.net	<1%
excite.com	<1%
fastmail.net	<1%
gmai.com	<1%
gouv.fr	<1%
h-mail.us	<1%
hotmail.ca	<1%
hotmailse.com	<1%
hotmalez.com	<1%
imajl.pl	<1%
jmail.com	<1%
juno.com	<1%
live.co.uk	<1%
mac.com	<1%
mailandftp.com	<1%
mailas.com	<1%
mailbolt.com	<1%
mailnew.com	<1%
mailservice.ms	<1%
modeperfect3.fr	<1%
mymacmail.com	<1%
nyc.gov	<1%
op.pl	<1%
peoplepc.com	<1%
petml.com	<1%
pornsex.com	<1%
qwest.net	<1%
rosefroze.com	<1%
sbcglobal.net	<1%
ssl-mail.com	<1%
t-online.com	<1%
thetrueonestop.com	<1%
turk.net	<1%
virgilio.it	<1%
virginmedia.com	<1%
windstream.net	<1%
yaahoo.co.uk	<1%
yahoo.com.my	<1%
yazobo.com	<1%
yopmail.com	<1%
zol.com	<1%

A few words of warning here. First, these figures are taken from comments that made it through the basic spam filter. Currently 90% of comments are rejected using a heuristic, and even more blocked by their IP address, so these are probably from real people who persisted rather than bots. They’re also sorted in order of hits and then alphabetically. In other words, they are ranked from worst to best, and therefore zol.com has least, or equal-least, multiple uses.

It’s interesting to note that gmail was by far the most popular choice (40%) when asked to provide a valid email address but when this was used to register this dropped to 7%, with Hotmail being the favourite followed by other freemail services popular in East Europe and Russia (many single-use and counted under “Other”). Does this mean that Gmail users get more hassle from Google when they misbehave? The use of outlook.com had an even bigger reduction in percentage terms – again suggesting it’s a favourite with abusers.

Another one worth noting is that mailnesia.com was clearly popular as a real address for registering spammers, but was not used even once as a fake address. This is another of those disposable email address web sites, Panamanian registered – probably worth blacklisting. emailgratis.info is also Panamania registered but heads to anonymous servers that appear to be in North Carolina.

Where you see <1% it means literally that, but it’s not insignificant. It could still mean hundreds of hits, as this is a sample of well over 20K attempts.

If you have WordPress blog and wish to extract the data, here’s how. This assumes that the MySQL database your using is called myblog, which of course it isn’t. The first file we’ll create is that belonging to registered users. It will consist of lines in the form email address <tab> hit count:

echo 'select user_email from wp_users ;' | mysql myblog | sed 1d | tr @ ' ' | awk '{ print $2 }' | sed '/^$/d' | sort | uniq -c | sort -n | awk '{ print $2 "\t" $1}' > registered-emails.txt

I have about a dozen registered users, and thousands of spammers, so there’s no real need to exclude the genuine ones for the statistics, but if it worries you, this will get a list of registered users who have posted valid comments:

select distinct user_email from wp_users join wp_comments where not comment_approved='spam' and ID=user_id;

To get a file of the email addresses of all those people who’ve posted a comment you’ve marked as spam, the following command is what you need:

echo "select comment_author_email from wp_comments where comment_approved='spam';" | mysql myblog | sed 1d | tr @ ' ' | awk '{ print $2 }' | sed '/^$/d' | sort | uniq -c | sort -n | awk '{ print $2 "\t " $1}' > spammer-emails.txt

If you want a list of IP addresses instead, try:

echo "select comment_author_IP from wp_comments where comment_approved='spam';" | mysql myblog | sed 1d | sort | uniq -c | sort -n | awk '{ print $2 "\t " $1}' > spammer-ip-addresses.txt

As I firewall out the worse offenders there’s no point in me publishing the results.

If you find out any interesting stats, do leave a comment.

22-July-13

David Cameron on Google Porn

I’ve been watching with dismay David Cameron’s statements on the Andrew Marr show at the weekend; he’s attacked Google and other big companies for not blocking illegal pornography. Let’s be clear: Google et al, already do, as far as is possible. The Prime Minister is simply playing politics, and in doing so is exposing his complete lack of understanding about matters technological and social.

It’s not just the coalition government; Edward Miliband trumped him in stupidity by saying that the proposed plans “didn’t go far enough”, which is his usual unthinking response to anything announced by the government that’s might be popular.

Cameron’s latest announcement is to force ISPs to turn on “no porn” filters for all households (optionally removed, so it’s not State censorship). I’d be fascinated to hear him explain how such a filter could possibly work, but as my understanding of quantum mathematics isn’t that good it I may yet be convinced. Don’t hold your breath waiting.

The majority of the population won’t be able to understand why this is technical nonsense, so let’s look at it from the social point-of-view. People using the Internet to distribute child-abuse images do not put them on web sites indexed by Google. If Google finds any, they will remove them from search results and tell the police, as would everyone else. Paedophiles simply don’t operate in the open – why would they? They’re engaged in a criminal activity and don’t want to be caught, and therefore use hidden parts of the Internet to communicate, and not web sites found by Google!

Examining the illegal drugs trade is a useful model. It’s against the law, harmful and regarded as “a bad thing” by the overwhelming majority. The police and border security spend a lot of time and money tackling it, but the demand remains and criminal gangs are happy to supply that demand. So how successful has 100 years of prohibition been? Totally ineffective, by any metric. With 80% of the prison population on drugs IN PRISON it should be obvious that criminals will continue to supply drugs under any circumstances, if there’s a demand. If anything, proscribing drugs has made it more difficult to deal with the collateral effects by making the trade and users much more difficult to track.

So, if we can’t stop drugs (a physical item) getting in to prisons (presumably amongst most secure buildings in the country) , does anyone seriously think it’s possible to beat the criminals and prevent illegal porn being transmitted electronically to millions of homes across the country? David Cameron’s advisors don’t appear to have been able get him to understand this point.

Another interesting question is whether I should opt to have the porn filter removed from my connection. The only way such a filter could possibly be effective is if it banned everything on its creation, and then only allowed what was proven safe through. There are generally considered to be over 500 million web sites out there, with 20,000 being added every month. That’s sites; not individual pages. The subset that can realistically be examined and monitored to make sure they are safe is going to be quite small, and as a security researcher, I need to retrieve everything. So am I going to have to ‘phone my ISP and say “yes please, want to look at porn”? Actually, that won’t be a problem for me because I am my own ISP. The government doesn’t even know I exist; there is no register of ISPs (or even a definition of the term). There are probably tens of thousands in the country. So I shall await a call from Mr Cameron’s office with a full technical explanation of this filtering scheme with interest.

Fortunately for the Prime Minister, his live speech on the subject scheduled for 11am has been displaced by a load of royal reporters standing outside a hospital and Buckingham Palace saying “no news yet” on the supposed imminent arrival of the Duke and Duchess of Cambridge’s first child.

3-July-133-July-13

New kind of distraction email bomb attack

I got an interesting note from AppRiver, in which Fred Touchette, one of their analysts explains a technique used by criminals, which they first noticed in January. I haven’t seen it, nor any evidence of specific cases, but it’s food for thought.

The idea is to mail-bomb a user with thousands of spam emails containing random content over a period of several hours. Mr Touchette’s theory is that this is done to cause the user to delete the whole lot unread, and in doing so to miss an important email from their bank or similar, and therefore fail to notice a fraud attempt.

I’m not so convinced about this MO to cover bank fraud, but it would certainly be useful to someone stealing a domain name. A registrar will contact the administrative contact with a chance to block the transfer of a domain when any attempt to move it is made. This is a weak system; banks would normally require positive confirmation and not rely on the receipt and reading of an email before doing anything drastic.

If the criminals have your email login, necessary to manage something like a bank account, they will have no need to prevent you from reading emails with a mail-bomb. They just have make sure they read and delete your mail before you do, which isn’t hard if they’re keen. AppRiver’s advice, nonetheless, is to call all your banks to warn them someone might be attempting to compromise your account. I’m sure they’ll thank you politely if you do.

You can read Appriver Threatscape Report for yourself. Most of it’s unsurprising if you follow threats yourself, but this detraction technique as an attack vector is worth taking seriously, regardless of its prevalence in the wild. AppRiver is based in Florida and provides web and email security and filtering services. I met them at a London trade show and they seemed like a decent bunch.

1-July-132-July-13

Pipe stdout to more than one process on FreeBSD

There are odd times when you may wish to use the stdout of a program as the stdin to more than one follow-on. bash lets you do this using a > to a command instead of just a file. I think the idea is that you just have to make sure the command is in ( ) and it works. One up to bash, but what about somthing that will work on standard shells?

The answer is to use a named pipe or fifo, and it’s a bit more hassle – but not too much more.

As an example, lets stick to the “hello world” theme. The command sed s/greeting/hello/ will replace the word “greeting” on stdin with “world” on stdout – everything else will pass through unchanged. Are you okay with that? Try it if you’re not comfortable with sed

Now I’m going to send a stdout to two different sed instances at once:

sed s/greeting/hello/
sed s/greeting/world/

To get my stdout for test purposes I’ll just use “echo greeting”. To pipe it to a single process we would use:

echo greeting | sed s/greeting/hi/

Our friend for the next part is the tee command (as in a T in plumbing). It copies stdin to two different places, stdout and (unfortunately for us) a file. Actually it can copy it to as many files as you specify, so it should probably have been called “manifold”, but this is too much to ask for an OS design that spells create without the training ‘e’.

Tee won’t send output to another processes stdin directly, but the files can be a fifos (named pipes). In older versions of UNIX you created a pipe with the mknod command, but since FreeBSD moved to character only files this is deprecated and you should use mkfifo instead. Solaris also uses mkfifo, and it came in as far back as 4.4BSD, but if you’re using something old or weird check the documentation. It’ll probably be something like mknod <pipename> .

Here’s an example of it in action, solving our problem:

mkfifo mypipe
sed s/greeting/hello/ < mypipe &
echo greeting | tee mypipe | sed s/greeting/world/  
rm mypipe

It works like this: First off we create a named pipe called mypipe. Next (and this is the trick), we run the first version of sed, specifying its input to come from “mypipe”. The trailing ‘&’ is very important. In case it had passed you by until now, it means run this command asynchronously – or in background mode. If we omitted it, sed would sit there waiting for input it would never receive, and we wouldn’t get the command prompt back to enter the further commands.

The third line has the tee command added to send a copy of stdout to the pipe (where the first sedis still waiting). The first copy is piped in the normal way to the second sed.

Finally we remove the pipe. It’s good to be tidy but it doesn’t matter if you want to leave it there use it again.

As a refinement, pipes with names like “mypipe” in the working directory could lead to trouble if you forgot to delete it or if another job picks the same name. Therefore it’s better to create them in the /tmp directory and add the current process ID to the name in order to avoid a clash. e.g.:

mkfifo /tmp/mypipe.1.$$

$$ expands to the process-ID, and I added a .1. in the example so I can expand the scheme to have multiple processes receiving the output – not just one. You can use tee to send to as many pipes and files as you wish.

If you run the example, you’ll probably get “hello world” output on two lines, but you might get “world hello”. The jobs have equal status, so there’s no way to of knowing which one will complete first, unless you decided to put sleep at the start of one for force the issue.

When I get around to it a more elaborate example might appear here.