Ben Clifford Technical Blog: shell

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28 January, 2012

one line to make your site look nice on iPhone

Well, I came across a magic line of HTML for making a website look basically readable on an iPhone. Not magic in the sense that I don't understand what it does. But magic in the sense that its a single line that is the first big step to making a site look OK.

The line is (to go in your <head> section:
<meta name="viewport" content="width = device-width" />

What it does is make the iPhone web browser render the HTML at a sensible readable font size, with word wrapping at the end of the screen. (the default, otherwise, is to try to fit a regular screen worth of pixels across, then zoom out to make it fit on the small iPhone screen - that means the user has to zoom and pan to do anything).

Now my pages still look like crappy hand written HTML, but at least they're readable on an iPhone now.

I added this to the shellinabox installation I have on barwen.ch, and now its much prettier to use a browser-based shell on an iphone - you get a 30 character terminal thats at sensible font size, rather than a wide wide terminal at unreadable font size.

16 July, 2011

browserid in-browser shell logins

I've previously wired up my shell server barwen.ch to allow browser-based logins using OpenID and shellinabox. I've written about that on this blog before. I saw a few articles about Mozilla's BrowserID. The code snippets there looked like they would integrate well with the code I had already. So my evening project (which ended up only taking about half an hour) was to prototype BrowserID-based shell login.

It works basically the same as for the OpenID login on barwen.ch:

To get set up: you need to sign up for a barwen.ch account which will cost you 50 cents on PayPal; you need to send me the email that you use for BrowserID (instead of / in addition to an SSH key).

To actually log in, go to the login page http://s0.barwen.ch/~benc/browserid.html and log in. A terminal will appear in your browser. You do shell stuff.

This code is pretty crappy so I don't really want to release it until I've had a thought about the security for at least an hour (though you can find fragments of it elsewhere on this blog). I especially think that there might be some attacks possible by using freaky email addresses vs my unsanitised string handling. (I'm looking at you, Bobby Tables).

12 June, 2010

rlwrap

I got frustrated when some application I was using *still* didn't support delete properly and discovered that the solution in that community (the OCaML world) seems to be (at least for commandline use) to use 'rlwrap' to add readline support to arbitrary applications.

eg:

$ rlwrap cat
Now you can use readline features (eg delete, cursor movement) to edit text

Neat.

http://utopia.knoware.nl/~hlub/rlwrap/

21 May, 2010

For reasons which might not be intuitively obvious, the broken behavior is required

I previously regarded /usr/bin/env as being portable onto any sane unix platform.

But now I've had to work with FreeBSD and my beliefs are dashed.

FreeBSD /usr/bin/env implements what posix says, rather than what everyone else does. That leads to trouble when you want to pass a parameter in a shebang, like this: #!/usr/bin/env perl -w which works almost everywhere but not in FreeBSD :(

07 May, 2010

making haskell EDSLs shebangable

There's a mindset that says to solve your problem, first write a language to solve your problem in, and then solve your problem in that language. And there's a mindset that says that your language should be an embedded language inside Haskell. In many ways that is appealing.

I wanted to write something that would delete old rsync snapshots. I took the domain-specific language approach, where the language specifies the retention policy for snapshots, like this:

policy = recent <||> weekly <||> monthly

meanings the final policy is to keep 'recent', 'weekly' and 'monthly' backups, with other statements defining what those three other policies mean. I won't write more about the language here - there's more on the webpage for the tool, snaprotate.

One particular piece of this I don't feel terribly comfortable with, and thats how to invoke/run the policy files.

I can imagine two different interfaces:

$ snaprotate -f policyfile

$ policyfile

I took the second approach, making policies first order unix executables - commands that can be run like any other command.

In unix tradition the way you indicate the language of a script is with a shebang line (#!/something) at the start of the script.

So then I want my scripts to look like something like this:

#!/usr/bin/snaprotate

policy = recent <||> weekly <||> monthly

This is almost a valid Haskell program, but: i) I need to import the SnapRotate module, and ii) I don't want to specify a main routine (which looks something like:

main = runPolicy policy

).

So the snaprotate commandline looks almost like runhaskell but does some source file rearranging to address the above two points, and to remove the #! shebang line.

#!/bin/bash
FN=$(mktemp /tmp/snaprotateXXXXX).hs
FNHS=$FN.hs
LIBDIR=$(dirname $0)

cat > $FNHS << 32804384892038493284093
import SnapRotate
main = runLevels policy

32804384892038493284093

cat $1 | grep --invert-match '^#!' >> $FNHS
shift
runhaskell -i$LIBDIR $FNHS $@

I wonder if this is the best way to implement such an embedding?

20 March, 2010

so many ways to hash

I was making commandline tools for stupid to drive the example sha256 code, resulting in multiple tools that deliberately did the same but using different language backends. Then I realised I have a shitload of (where shitload==4) md5sum commandline tools already:

$ echo abc | md5
0bee89b07a248e27c83fc3d5951213c1

$ echo abc | gmd5sum
0bee89b07a248e27c83fc3d5951213c1  -

$ echo abc | openssl dgst 
0bee89b07a248e27c83fc3d5951213c1

$ echo abc | gpg2 --print-md md5
0B EE 89 B0 7A 24 8E 27  C8 3F C3 D5 95 12 13 C1

13 March, 2010

seq

You(*) whisper to X, "the same package [GNU coreutils] which provides seq"
You(*) whisper to X, "the command line utility"
You(*) whisper to X, "also provides factor"
You(*) whisper to X, "which outputs prime factors"
You(*) whisper to X, "makes me want to start making fucked up shell scripts"
You(*) whisper to X, "that use goedel numbering"
You(*) whisper to X, "for some purpose."
You(*) whisper to X, "i have to wonder how a commandline utility for factoring primes is 'core' in any way, though"

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