Easily get your external IP address using the terminal or command line

I want my little Raspberry Pi to "phone home" once in a while so I know where it's at. I wanted a very simple web service that simply regurgitated the requester's IP address in plain text. Nothing more, nothing less.

About to write it myself, I typed in echoip.com and found exactly what I wanted. It's been a good day!

To get your external IP address from the command line or Linux terminal:

$ curl echoip.com

To save it to a file:

$ curl -s echoip.com > myip

Or, if you prefer wget:

$ wget echoip.com --no-cache -qO-

To get super-nerdy and make your life even easier:

$ alias echoip="curl echoip.com"

$ echoip

(You could use any of the variations above for your alias' command.)

In the end, this is the command I added to my Raspberry Pi's crontab (I've changed sensitive parts):

$ curl -s echoip.com | ssh user@mysite.com "cat > /www/mysite/ipaddress.txt"

As a side note, if you want JSON output, there's jsonip.com, or for XML, there's xmlip.com (which actually does XML, JSON, and plain-text, but I feel like the server is a bit slower -- and the homepage doesn't actually serve XML. *facepalm*)

I don't know who made echoip.com, but props to them for choosing the same name I would have. (For some reason, I thought that the output at plainip.com would be... well, plainer.) Memo to self: if echoip ever goes offline, write my own to replace it.

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Using Vagrant and cross-compiling Go (golang)

This is mostly a memo-to-self about how to write Go code in my Mac environment, compile it there for a Linux environment, and run it in a production-like Linux environment using Vagrant.

If using Homebrew...

My Go installation was home-brewed. If you used Homebrew to install Go, you need to make sure you did with the --cross-compile-common flag. If not, no problem, just run these:

$ brew update
$ brew upgrade go --cross-compile-common

Or do --cross-compile-all for all supported platforms.

If not using Homebrew...

If you're not using a Homebrew install of Go, you need to make Go support cross-compilation yourself. First you just need to tell Go to put the package files for the other architecture(s) in its pkg directory.

$ cd /usr/local/go/src

$ sudo GOOS=linux GOARCH=amd64 CGO_ENABLED=0 ./make.bash --no-clean

For GOOS, you can specify linux, darwin (for Mac), windows, and freebsd. For GOARCH, you can specify amd64, 386 (for 32-bit), and arm. As of Go 1.1, cgo is disabled by default, so the CGO_ENABLED part isn't necessary if you're setting it to 0, but to enable it you'll need to set it to 1.

Cross-compile your Go program

Once the make is finished, you can change into your Go program's directory and build or install like this:

$ GOOS=linux GOARCH=amd64 go build -o myprogram.linux64 prog.go

myprogram.linux is what I'm calling the output file in this case to remind me that the binary is for 64-bit Linux systems. For Windows, you'd want to call it something ending in .exe. Finally, prog.go is the name of my source file.

You can also do an install instead of just a build using the same technique.

Set it up with Vagrant

Coming soon.

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Why yes, Go/Golang, I still want to read my CSV file!

UPDATE: This appears to have been fixed and the fix ships with Go 1.2.

I like Go (1.1.1), but how disappointing that in order to read this:

1,O1,,,,0.0000,0.0000,,
2,AP,,,,35.0000,105.0000,,
3,EU,,,,47.0000,8.0000,,
4,AD,,,,42.5000,1.5000,,

I need to tell this code:

csvFile, err := os.Open("/path/myfile.csv")
defer csvFile.Close()
if err != nil {
    panic(err)
}
csvReader := csv.NewReader(csvFile)
for {
    fields, err := csvReader.Read()
    if err == io.EOF {
        break
    } else if err != nil {
        panic(err)
    }
    // ... do stuff ...
}

to allow the last field in any row to be empty:

csvReader.TrailingComma = true

Otherwise:

panic: line 1, column 22: extra delimiter at end of line

Really??

One word: BIZARRE.

Even though my dissatisfaction with Go is quite low, this is probably my biggest disappointment so far. It's an obscure, barely-documented bug feature in the encoding/csv package that will have you scratching your head because your CSV file is perfectly formatted. It's all thanks to this fine logic:

// We don't allow trailing commas.

So by trailing comma, they really mean, empty last fields. Um. Why.

Doesn't Go REQUIRE trailing commas when defining map and struct literals? Why forbid them here? Kind of odd considering it's an engineered language.

A line break or comma in the data would enclose the field in quotes... so a comma at the end of a line must mean that the last field is... empty. That is all.

O little csv.Reader, your name is Reader, not SyntaxChecker. Leave it to the file's author to fix those flaws. But please, just read this properly-formatted CSV file in all its little glory. That's all I ask of you, csv.Reader... that's all I ask...

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