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Inline text replacement with sed

Replacing values in files is incredibly easy with sed. Here’s some examples:

 

sed 's/match/replace/g' file.txt

Find match, replace with replace, globally (all matches), in file.txt

 

sed 's/match/replace/g' file.txt > file2.txt

Same as before, but write results to new file, file2.txt

 

sed -n 's/match/replace/p' file.txt

-n suppresses output of the results, but /p prints out just the matching patterns that are replaced.

 

sed -i.old 's/match/replace/g' file.txt

Replace matches in the input file with inline replace (-i), renaming original file file.txt.old and writing inline replace results to file.txt

 

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Node.js and Mongoose: connection hanging on find()

Following this tutorial to build a simple REST api on Node.js with Express, attempting to retrieve all docs from my MongoDB gave these errors:

2016-05-19T20:10:47.311-0700 [initandlisten] connection accepted from 127.0.0.1:52053 #4 (2 connections now open)

2016-05-19T20:10:47.325-0700 [conn4]  authenticate db: nodetest { authenticate: 1, user: "", nonce: "xxx", key: "xxx" }

2016-05-19T20:10:47.336-0700 [conn4] Failed to authenticate @nodetest with mechanism MONGODB-CR: ProtocolError field missing/wrong type in received authenticate command

Some quick Googling turned up the same error in this post that just suggested authentication was failing because no user was passed. So created a new used with:

db.createUser({user : 'nodetest', pwd: 'passwordhere', roles: ['readWrite', 'nodetest']})

… and problem solved.

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Update: onscreen keyboard for Raspberry Pi 7″ touchscreen

Quick followup from last week’s post on setting up an onscreen keyboard. I couldn’t find a way of getting an onscreen keyboard, either matchbox-keyboard or florence, to respond on Raspbian’s logon screen. Rather than spend more time on investigating this, I just enabled the logon to desktop in raspi-config, and now logged on, either of the keyboards work as expected, perfectly well.

Florence seems to be the better of the two I tried. Once opened from the menu you can drag it around, or minimize it to a keyboard icon, so you can pop-it open as needed.

If I could get it to work from the logon screen too that would be awesome, but avoiding that issue and once you get to the desktop, it works great.

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Common dipole antenna dimensions for Amateur Radio HF bands

When building your own antennas, you can either look up a design or dimensions online or from book, or you can use a common formula. 468/MHz is commonly used to calculate the total length of a wire dipole in feet. I had a few dimensions jotted down for reference, but it’s easy to stick the formula into a spreadsheet and just enter the freqs you’re interested in. For example, here’s a Google Doc with the common HF bands:

I hope I’ve got these right, but if not, drop me a comment below.

Here’s a link direct to the Google Sheet if you’d like to bookmark it: https://docs.google.com/spreadsheets/d/1d3Mmnyzvj8AG1lFPd59RSMJhE9ihbE2M4w5noDzyedo/edit?usp=sharing

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