Case Study for Bash and Node - __dirname

Posted by Dave Eddy on 13 Apr 2015 - tags: tech

__dirname is a variable that is available to all scripts that are run by Node.JS - it contains a string that refers to the directory name where the currently executing script is contained. The variable is set on a per-file basis, so any script that is sourced using require will have its own __dirname variable that points to the directory where the script itself is contained.

Example In Node

Take the following node script located at /tmp/node-one

console.log(__dirname);

When executed, we can see

$ node /tmp/node-one
/tmp
$ cp /tmp/node-one /var/tmp/node-one
$ node /var/tmp/node-one
/var/tmp
$ cp /tmp/node-one ~/node-one
$ node ~/node-one
/home/dave

And, when using require, given the following script in ~/two.js

require('/tmp/node-one');

When executed, we can see

$ node ~/two.js
/tmp

Even though ~/two.js resides in /home/dave, it prints /tmp becasue the script being sourced resides in /tmp.

Because of this behavior, it is very easy and elegant for node scripts to require one another without needing to know an absolute path ahead of time. By using only relative require statements, all paths will be made relative to __dirname implicitly.

Problems

This behavior however, relies on very specific situations for the script to be executed. Imagine the case where node does not know where the JavaScript bytes are coming from. For example, using the original node-one script above:

Read More...


WeeChat perl plugin on SmartOS

Posted by Dave Eddy on 30 Mar 2015 - tags: tech

Here's a quick hack to get the perl plugin working for WeeChat on the latest (2014Q4) SmartOS

weechat is now in pkgsrc, but it appears to have been built without perl support, which renders certain plugins not working with errors like:

/script install pushover.pl
script: script "pushover.pl" can not be installed because plugin "perl" is not loaded
/plugin load perl
Error: unable to load plugin "perl": ld.so.1: weechat: fatal: perl: open failed: No such file or directory
If you're trying to load a script and not a C plugin, try command to load scripts (/perl, /python, ...)

How

To quickly work around this:

1 install weechat from pkgsrc

pkgin in weechat

This will install weechat without the perl plugin

2 compile weechat at the same version from source

wget https://weechat.org/files/src/weechat-1.0.tar.gz
tar xzf weechat-1.0.tar.gz
cd weechat-1.0
mkdir build
cd build
cmake ../ -DPREFIX=/opt/local
make

THIS WILL FAIL, version 1.0 does not compile cleanly on SmartOS. However, perl.so has been built, which is all we need

3 move the plugin into place

sudo cp ./src/plugins/perl/perl.so /opt/local/lib/weechat/plugins/

4 it works

/plugin load perl will now work as expected

TODO

  1. have weechat in pkgsrc built with perl support - https://github.com/joyent/pkgsrc/issues/252
  2. fix weechat build problems on SmartOS - https://github.com/weechat/weechat/issues/381

Human Readable Duration in Bash

Posted by Dave Eddy on 29 Jun 2014 - tags: tech

show seconds in a human-readable form using pure bash

This function provides a simple way to turn a number of seconds into a human readable form using minutes, hours, days, etc. For example.

$ human 50
50 seconds
$ human 600
10 minutes
$ human 75890
21 hours
$ human 475890
5 days
$ echo "bash has been running for $(human "$SECONDS")"
bash has been running for 2 minutes

The Code

human() {
    local seconds=$1
    if ((seconds < 0)); then
        ((seconds *= -1))
    fi

    local times=(
    $((seconds / 60 / 60 / 24 / 365)) # years
    $((seconds / 60 / 60 / 24 / 30))  # months
    $((seconds / 60 / 60 / 24 / 7))   # weeks
    $((seconds / 60 / 60 / 24))       # days
    $((seconds / 60 / 60))            # hours
    $((seconds / 60))                 # minutes
    $((seconds))                      # seconds
    )
    local names=(year month week day hour minute second)

    local i
    for ((i = 0; i < ${#names[@]}; i++)); do
        if ((${times[$i]} > 1)); then
            echo "${times[$i]} ${names[$i]}s"
            return
        elif ((${times[$i]} == 1)); then
            echo "${times[$i]} ${names[$i]}"
            return
        fi
    done
    echo '0 seconds'
}

MIT License


Cross-Platform Implementation of which

Posted by Dave Eddy on 22 May 2014 - tags: tech

binfind

find the path of a binary in your PATH using only bash

The tool which(1) has many different implementations on many different operating systems. Because of this, its output and return codes are not well-defined, and should not be trusted in the context of a script. However, it is often desirable to determine if an executable exists on a filesystem, without having to fork the executable itself to test.

The algorithm which(1) uses is fairly simple: loop over all paths found in the environmental variable PATH, and test for the existence, and executable bit, of the binary in question.

The function below will search your PATH for the binary name given as the first argument, and print the full path of the first binary found and return 0 if it is successful. Otherwise, it won't print anything, and will return 1.

binfind() {
    local paths path
    IFS=: read -a paths <<< "$PATH"
    for path in "${paths[@]}"; do
        path=${path:-.}/$1
        if [[ -x $path ]]; then
            echo "$path"
            return 0
        fi
    done
    return 1
}

Example usage

$ binfind echo
/bin/echo
$ binfind clang
/usr/bin/clang
$ binfind foobar
$ echo $?
1

Directory Management with cd

Posted by Dave Eddy on 14 Sep 2013 - tags: tech

You cd around like you normally would, and the directories are pushed into a stack. Use the function s to view the stack of directories, and run s "$num" to cd into the directory listed. Use b to jump back 1 directory.

I was inspired by this article written by Derek Wyatt about directory management in BASH. The code I've written for this accomplishes most of the same tasks, but does so with about 1/3 of the code, as this was written specifically for BASH (no legacy KSH bits) and doesn't implement any of the fancier features for cd.

Example

In the above example I cd around a bit, and then run s to see what the current stack looks like. The current stacks shows all of my previous directories in reverse order (limited to $CD_STACK_MAX entries, which defaults to 15).

The code is on GitHub here https://github.com/bahamas10/bash-cdstack


What's Open Now?

Posted by Dave Eddy on 18 Jun 2013 - tags: tech

You sit down to watch the LMN premier of Drew Peterson: Untouchable, when next thing you know, you just watched LMN for the last 6 hours, it is now 4am, and you're hungry. The obvious question is "What's open?", but where do you find the answer?

What's Open has the answer.

What's Open is a free service that uses Google Maps to show what places are around you are currently open.

whats-open

Skye came up with the idea, and I wrote the code.

You can view the site here http://whatsopen.pw

As well as view the source code here https://github.com/bahamas10/whats-open


Synchronous File IO in Node.js

Posted by Dave Eddy on 26 Mar 2013 - tags: tech

Does calling fs.writeFileSync trigger a synchronous write to the file system?

If you are familiar with Node.js, or have at least heard of it, you've most likely heard that it uses non-blocking IO, and lets you do work asynchronously. One of the most basic APIs that Node provides is for the file system; With this API, you can read, write, remove, etc. files and do other file system related tasks and modifications.

This API follows a standard pattern of exposing 2 functions for each operation: one for asynchronous work, and the other for synchronous work. For example, if you want to read a file in Node you can do so asynchronously:

var fs = require('fs');
fs.readFile('/etc/passwd', function(err, buf) {
  console.log(buf.toString());
});

Node will continue executing any javascript code it encounters while reading the file. Once all javascript is done being executed and the file is ready, it will run the anonymous function and print the file contents.

Read More...




Unfreeze Photoshop

Posted by Dave Eddy on 27 Feb 2013 - tags: tech

Unfreeze a frozen Photoshop on Mac

I wrote an app to unfreeze a stuck or frozen photoshop. If you're running photoshop, and it starts beachballing, or not responding on you, try running this. This application will help if suddenly you have a frozen photoshop, and you want to fix it.

Download the app

screenshot

Read more about it here