ssh port forwarding without starting a new session

December 10, 2008

You can forward ports with ssh like this:

$ ssh -L 8080:localhost:80 user@remotehost

This will log you in to remotehost as user, and port 8080 on your local machine will be tunnelled to port 80 on remotehost. If remotehost can see a machine that you can’t (for example, if it’s on an internal network), you can even do this:

$ ssh -L 8080:internalhost:80 user@borderhost

This will log you in to borderhost, and localhost:8080 will be directed to internalhost:80, even though you may not be able to see internalhost directly yourself.

What I didn’t know until I read Nico Golde’s blog today, is that you can do this interactively, with an existing session. Tilde (~) is the default escape character, and ~C (note that’s an uppercase C) gets you a shell session within ssh itself:

$ ssh user@remotehost
user@remotehost$ ~C
ssh> -L 8080:localhost:80
Forwarding port.
user@remotehost$


Book

April 23, 2008

A serious publisher has contacted me about writing a serious book about Linux shell programming.

It is all really very serious. I’m not used to being serious, as you can probably tell from the fact that I have now used the word “serious” four times in this three-sentence post.

I am rather keen to write a book on the subject, not because I’m vain, or desperate for money, but because the stuff I have seen out there in dead-tree format has been of rather low quality. Also because of all the emails I’ve received over the years, they have all been positive, and none has said anything along the lines of “I didn’t need any of that because I bought Book[X]“, or indeed any book. People have emailed me, asking for advice as to what book to buy, and I have been unable to recommend any book that I have seen.

So:

What would you like to see in your ideal book about UNIX / Linux shell scripting, be it Bourne, Bash, ksh, tcsh, zsh, whatever?

Please don’t be timid; if you want to know how to work out how many nose-flutes can be fitted into the area of a Boeing 757, you won’t be anything like as strange as some of the correspondants I’ve had over the years, so please, tell me what is bugging you, what has bugged you, or even what you think might be likely to bug you in days / months / years to come.

I’m likely to answer any specific questions here and now, whether or not they end up in the book, but anything you’d like to see in a book, too… post that here, and I’ll have a stab at it.

Also, I would of course be interested to know if you have found any useful books on or around the subject, and what they did particularly well.

Steve


Happy First Birthday!

January 6, 2008

This blog has now been running for a year; the first post was Hello World on 17th Jan 2007.

I hadn’t realised it had been going for so long; in that time, I’ve made 41 posts, so I haven’t quite managed to make one post per week :( I have been a bit slack lately, for which I do apologise. New Years Resolution: I must make more posts here!

In the meantime, my main site, steve-parker.org, has celebrated its seventh birthday, having been born in June 2000 – looking forward to making the 8th birthday celebrations this June!


Redirection – Simple Stuff

May 30, 2007

Nobody deals with the really low-level stuff any more; I learned it from UNIX Gurus in the 90s. I was really lucky to have met some real experts, and was stupid not to have better understood the opportunity to pick their brains.

Write to a file

$ echo foo > file

Append to a file

$ echo foo >> file

Read from a file (1)

$ cat < file

Read from a file (2)

$ cat file

Read lines from a file

$ while read f
> do
>   echo LINE: $f
> done < file
$

Regular Expressions

April 18, 2007

http://etext.lib.virginia.edu/services/helpsheets/unix/regex.html has a good introduction to Regular Expressions – grep, sed, and friends.

It includes a brief discussion on Backreferences (aka “the stuff that * matched”)


More maths stuff – bc in detail

April 8, 2007

There’s a great post about bc at basicallytech.com – I think that I’ve already covered most of the same ground, but it’s got lots of great examples.


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