::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact

Reading Manpages On The Train

May 12th, 2011
tech  [html]
Stuck on the red line from 6:45 to 7:39. Every few minutes we were told we would be moving 'momentarily'. Forgot my book. Reading manpages. So far I've learned:
  • ssh supports visual host keys
    • When you ssh into somewhere you've sshed into before from this computer, checking that the host key has not changed is easy and automatic. When logging in from a different computer, though, the 'right' thing to do is to check the host fingerprint manually. This is impractical. The idea of a visual host key is that if you trust the computer you're on but not the connection it will display a pictoral representation of the fingerprint. This should be relatively easy to compare with a memorized one from past logins.
    • It also supports putting fingerprints in the dns, though I've never heard of anyone doing that. Perhaps before DNSSEC (which is only just starting to be available) it wasn't so useful because someone that could man in the middle your ssh could just as easily man in the middle your dns?
  • bash will generate sequences with '{N..M}' so '{1..5}' means '1 2 3 4 5'
  • If you have A=1 B=A and want to do ${${B}} to mean ${A} to mean 1, you can't do it. Bash refuses to double expand. Instead you have to do ${!B} which is called indirect expansion. If you also have C=B I don't see a way to do ${!!C} and have a doubly indirect variable reference. I don't see why the didn't go for what I would find intuitive and do ${${B}} or ${${${C}}} along the model of $($(echo 'echo foo')) which does what I would expect it to (expands twice, finally echoing 'foo').
  • I knew bash supported '(...)' to do process substitution for writing, as in "log_results --outfile >(grep foo)".
The especially annoying thing about being stuck is that the first third of our waiting was at harvard station with the doors closed. I would have gotten out and taken the 77 if they had let us. Instead they keep the doors closed. Now we're stuck in the tunnel between davis and porter and they're telling us they're going to reverse back to harvard. Now I'm on a bus. At least it wasn't so delayed that my free transfer expired.

Comment via: facebook

Recent posts on blogs I like:

Incoming Gantz-Led Government to Invest in Israel’s Infrastructure

Israel’s incoming prime minister Benny Gantz unveiled an emergency government, to take power following an upcoming confidence vote in the Knesset. The last two MKs required to give Gantz a 61-59 majority, two members of Gantz’s own Blue and White Party wh…

via Pedestrian Observations April 1, 2020

Finding home in the time of coronavirus

Disclaimer: I’m going to say this once. Obviously, I am not happy about the coronavirus’s threat to public health or the economic toll it’s taking. I do not think the existence of this pandemic is good. Just so happens that social distancing and remote wo…

via Holly Elmore March 31, 2020

Massachusetts should shut down immediately

We’ve been running 30x fewer tests than other states, and have been extremely tardy in responding to the Biogen outbreak.

via benkuhn.net March 15, 2020

more     (via openring)

More Posts:


  ::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact