Jerzy's Notes

echo on Linux does not need quotes

Sun, 29 May 2016 00:00:00 +0000

The echo command in Linux does not require quotes: echo Hi there blog readers …will output the same as: echo "Hi there blog readers" The obvious exception is when the string to be printed contains special characters that would confuse echo itself, in which case quotations may be necessary.

How I use ls on Linux

Sat, 28 May 2016 00:00:00 +0000

When I run ls, I run it as ls -lAhog: l says to put each file or folder on its own line A says to list all files – hidden files, backups, etc. – but omit the current directory (.) and the parent directory (..) h says to use human readable file sizes – 1.5G instead of 1628688384 g says to omit the user o says to omit the group Occasionally I use the -R parameter, which lists folders and subfolders recursively.

How to rename a hash key in Ruby

Sat, 28 May 2016 00:00:00 +0000

Assume you have a Ruby Hash with the regions of the United States: $ usa_regions => {"northeast"=>11, "southeast"=>12, "midwest"=>12, "southwest"=>4, "rest"=>9} But instead of calling the West the rest, you want to rename it to west. Here’s how you would do that: $ usa_regions["west"] = usa_regions.delete("rest") Now, usa_regions has a hash key named west instead of rest. Importantly, the value of rest – 9 – has been preserved and assigned to west:

How to change the root password on MySQL

Mon, 01 Feb 2016 00:00:00 +0000

Sometimes the simplest sysadmin tasks are the hardest to find straightforward answers to. Recently, I spent too much time trying to change the root password on a fresh mysql install. Changing the root password for MySQL has security implications; there is no shortage of paranoid nerds describing how the world might end if you do what I’m about to do. If you understand the security implications of setting the root MySQL password, and still want to do it anyway, here’s how:

Location of the systemwide crontab on CentOS

Sun, 31 Jan 2016 00:00:00 +0000

The systemwide crontab file on CentOS can be found at /etc/crontab You can edit it with your editor of choice, e.g. sudo vi /etc/crontab

"No distributions at all found for..." & "Could not find any downloads that satisfy the requirement..." errors in Pip and PyPI

Thu, 28 Jan 2016 00:00:00 +0000

Recently, my team members starting seeing intermittent install errors from pip. Python packages that had installed days, hours, or even minutes ago suddenly became unavailable when pip install was run.

The Case for ToolsOps

Sat, 05 Dec 2015 00:00:00 +0000

Today, an overwhelming amount of software tools are available for developers. There’s data stores and Javascript frameworks and compilers and IDE’s and CI servers and browser extensions and virtualization suites and deployment tools and ETL toolkits and ORM’s and configuration managers and minifiers and CSS frameworks. And that’s only scratching the surface. And the list is growing fast.

Location of Wordpress' php.ini file in Ubuntu

Fri, 09 Jan 2015 00:00:00 +0000

/etc/php5/apache2/php.ini

How to use mdfind to search for every file on OS X

Tue, 06 Jan 2015 00:00:00 +0000

Spotlight is great, but it has some mom-friendly rules that limit the results. Since I’m a power user, I typically want to search the entire computer and see all results. Therefore, I use the mdfind command to search OS X. Just pop open Terminal and type: mdfind "income tax" This will search for all files with the metadata words “income tax.”

How to get and set model data from inside a Rails model

Mon, 05 Jan 2015 00:00:00 +0000

How to get the my_var model variable: puts self.var or puts var How to set the my_var model variable: self.var = "new value" Note that when setting, you must prefix with self., unlike when getting. Also note that @var will not work for setting or getting model data, ever.

How to list all MySQL databases on a server

Mon, 05 Jan 2015 00:00:00 +0000

SHOWdatabases;

Solution to the "Coin Maker" computer science interview question, using Ruby

Mon, 05 Jan 2015 00:00:00 +0000

A common computer science interview question goes something like this:

“Write a program that makes change with a minimum amount of coins for a given amount – a ‘Coin Maker’, if you will. You have unlimited amount of 1¢, 5¢, 10¢, and 25¢ coins. For example, $2.16 would consist of 8 quarters, 1 dime, 1 nickle, and 1 penny: 11 total coins.”

It's okay to make non-RESTful controllers & routes in Rails

Tue, 30 Dec 2014 00:00:00 +0000

As part of my ongoing professional education, I’ve decided to read through several Ruby on Rails projects on Github. It has been a great experience, and I am learning a lot. It’s insightful to see where I’m better than other software architects, and where I have room to grow – there are some very nuanced lessons to learn, and some very simple ones. This is one of the very simple ones.

Vagrant cheat sheet

Sun, 21 Dec 2014 00:00:00 +0000

Developing robust software requires an accurate testing and staging environment. Vagrant provides just that. It lets you mimic your production server map on your computer.

:dependent => :destroy vs. :dependent => :delete_all in Rails models

Sat, 20 Dec 2014 00:00:00 +0000

If you use :dependent => :destroy in your Rails model, each model to be destroyed will be instantiated and the destroy() method will be called upon it. This will result in the normal object destruction lifecycle, include any callbacks. Destroying children and grandchildren can be handled gracefully. It is a safe, normal way to destroy objects. If you’re not sure whether to use :dependent => :destroy or :dependent => :delete_all, use :dependent => destroy.

Don't use t.integer for referencing related tables in Rails migrations

Sat, 20 Dec 2014 00:00:00 +0000

Instead, use: create_table :address do |t| t.references :person end

Get a list of every Vagrant VM running on your computer

Sat, 20 Dec 2014 00:00:00 +0000

vagrant global-status

How to bind Vagrant to port 80 on OS X

Sat, 20 Dec 2014 00:00:00 +0000

First, stop Apache. Apache listens on port 80. If it’s running, Vagrant won’t be able to bind a VM to listen on port 80. Then, just add a forwarded port to your Vagrantfile: config.vm.network "forwarded_port", guest: 80, host: 80 And boot up Vagrant as sudo: sudo vagrant up

How to figure out which processes is listening on a port on OS X

Sat, 20 Dec 2014 00:00:00 +0000

sudo lsof -n -i4TCP:$PORT | grep LISTEN Replace $PORT with the port you are looking for This only works with TCP ports. Prefixing with sudo will show proceses the current user does not own

How to start and stop Apache in OS X

Sat, 20 Dec 2014 00:00:00 +0000

How to start Apache: sudo apachectl start How to stop Apache: sudo apachectl stop How to restart Apache: sudo apachectl restart N.B. I am on OS X Mavericks. It ships with Apache 2.

Rails' link_to always gives me a headache

Sat, 20 Dec 2014 00:00:00 +0000

After 9 years of writing Ruby on Rails code, link_to() never ceases to trip me up. Does it trip you up, too? Here are some quick notes: The first argument is what you want inside the <a> tag. For example link_to("today's news") produces <a>today's news</a> The second argument is the href attribute value. For example, link_to("today's news", "www.news.com") produces <a href="www.news.com">today's news</a> The third argument is a hash that contains everything else – most importantly, your <a> tag attributes.

View all valid URL routes in a Rails app

Sat, 20 Dec 2014 00:00:00 +0000

rake routes

What is the ./bin directory in a Ruby on Rails project?

Sat, 20 Dec 2014 00:00:00 +0000

Introduced in Rails 4, the ./bin directory contains your app’s “binstubs.” Binstubs are wrappers around gem executables, like rails or bundle, which ensures a gem executable is run inside the correct environment for your Rails app.

The Ruby on Rails folder structure

Fri, 19 Dec 2014 00:00:00 +0000

When a new Ruby on Rails project is created with rails new, many files and folders are created inside your project folder. Here’s a quick reference of what those are.

How to assign a variable based on a condition in Ruby

Thu, 18 Dec 2014 00:00:00 +0000

If you need to assign a variable based on a conditional, most programmers would do something like this:

result = nil
if condition == true
 result = 1
else
 result = 2
end
puts "The result is {result}."

I usually cringe when people say things like, “Oh, that’s a very C way of doing that”… but in this case, well, that’s a very C way of doing that.

How to delete all rows in a MySQL or Oracle table

Thu, 18 Dec 2014 00:00:00 +0000

There are two methods: DELETEFROMtable_name or TRUNCATETABLEtable_name The latter is more efficient, because it does not reference each row before deleting; it is a bulk operation. The former is expanded into DELETE * FROM table_name, which works on one row at a time. Therefore, use the latter.

How to list all rake tasks

Thu, 18 Dec 2014 00:00:00 +0000

rake -T -A This command will print out all available rake tasks. You can use it with Rails’ Rakefile, or with a custom Rakefile. N.B.: not all tasks have descriptions, and that is okay.

How to open the database's CLI in Ruby on Rails

Thu, 18 Dec 2014 00:00:00 +0000

rails dbconsole

Should I use MySQL or PostgreSQL with Ruby on Rails?

Thu, 18 Dec 2014 00:00:00 +0000

PostgreSQL. (Updated for 2015.)

Bash cheat sheet

Wed, 17 Dec 2014 00:00:00 +0000

Technically, this is a bash cheat sheet; however, many of the commands will work with Bourne shell descendants, such as zsh.

The only way that actually works to clear the screen in tmux

Tue, 16 Dec 2014 00:00:00 +0000

It was like pulling teeth to figure out a way to clear the screen in tmux, such as CMD+K does in Terminal.app and iTerm. Add this line to your tmux.conf. It Just Works™: bind -n C-k send-keys -R \; send-keys C-l \; clear-history

Using attr_accessor in Rails model classes

Tue, 16 Dec 2014 00:00:00 +0000

Don’t confuse attr_accessor and attr_accessible – they have very similar names attr_accessor is a pure Ruby function to create reader and writer methods for an instance variable attr_accessible is a pre-Rails 4 function to list the model attributes (e.g., database fields) that can be set via mass assignment, providing access control You can use attr_accessor on a Rails model to create non-persisted instance variables. For example: class Stock attr_accessor :current_price end This allows you to get the @current_price of a stock – something that would make no sense to persist.

How to create a database in MySQL

Mon, 15 Dec 2014 00:00:00 +0000

CREATEDATABASEmy_db;

How to ensure multiple ActiveRecord calls happen sequentially

Mon, 15 Dec 2014 00:00:00 +0000

ActiveRecord::Base.transaction do savings.withdrawal(100) checking.deposit(100) end If any exceptions are raised, the entire operation is rolled back on the database layer and nothing will be committed to the database.

How to run Javascript code on Mac OS X

Mon, 15 Dec 2014 00:00:00 +0000

When developing Javascript, you may wish to run code outside the browser. Luckily OS X comes with a world-class Javascript engine, which features a command-line interpreter. Since it’s hidden deep inside a framework, create a symbolic link: sudo ln -s /System/Library/Frameworks/JavaScriptCore.framework/Resources/jsc /usr/local/bin/js Now, you can enter the interpreter by simply typing: js The interpreter can be quit by typing quit(); or ctrl+c.

tmux cheat sheet

Mon, 15 Dec 2014 00:00:00 +0000

Since switching to vim, I’ve found myself really enjoying keyboard-based user interfaces. So instead of managing multiple terminal sessions in iTerm, I have started using tmux. I’m writing this cheat sheet as I learn. Check back often.

Where is Finder.app located on OS X?

Mon, 15 Dec 2014 00:00:00 +0000

/System/Library/CoreServices/Finder.app

How to use sshkit in vanilla Ruby (without Rails)

Mon, 08 Dec 2014 00:00:00 +0000

require 'rake' require 'sshkit' require 'sshkit/dsl' # your code goes here

How to start and stop MySQL on OS X

Sat, 06 Dec 2014 00:00:00 +0000

To start MySQL on OS X: mysql.server start To stop MySQL on OS X: mysql.server stop

How to sum in Excel when you have non-numeric fields

Sat, 06 Dec 2014 00:00:00 +0000

When building spreadsheets, I often SUM() up large sets of numbers in Excel. However, a common problem arises when you want to write --- or N/A to signify that a cell is intentionally empty. This causes SUM() to error.

How to get a list of open files for a process

Wed, 19 Nov 2014 00:00:00 +0000

lsof -p PID_NUMBER

How to put a prompt before gets.chomp in Ruby

Tue, 18 Nov 2014 00:00:00 +0000

Do you want to ask the user for input at the command line, using a slick 1980’s hacker movie prompt like this: >>? Don’t use gets.chomp. Use readline instead: require 'readline' Readline.readline(">>") …will output: >> I can write stuff here

Moving around in Linux with pushd, popd, and dirs

Tue, 18 Nov 2014 00:00:00 +0000

Often when administering a Linux server, you move around between the same few directories. You cd here, you cd there, and then you cd back here. Instead of cd‘ing so much, Linux has 3 powerful commands that can help you: pushd, popd, and dirs.

My ssh config file template

Tue, 18 Nov 2014 00:00:00 +0000

If you ssh into servers, you must set up a .ssh/config file. It will allow you to type ssh myd instead of ssh myuser@mydomain.com -i ~/.ssh/mykey.pem -p 1234.

reverse-i-search'ing in the Linux shell

Tue, 18 Nov 2014 00:00:00 +0000

When you press ctrl+r in the shell, you activate a feature called “reverse-i-search.” Reverse-i-search’ing lets you search through your shell history commands, from most recent to oldest.

Should I use gets.chomp or Readline for user input in Ruby?

Tue, 18 Nov 2014 00:00:00 +0000

Use Readline.readline(). That’s what irb uses for user input. Don’t use gets.chomp.

How to delete a database in SQL

Mon, 17 Nov 2014 00:00:00 +0000

DROPDATABASEname_of_database_goes_here;

How to get rid of control characters like ^[[D in Ruby's gets.chomp

Mon, 17 Nov 2014 00:00:00 +0000

You’re coding some Ruby. You use gets.chomp to get user input. You run your ruby file. You type some text at the prompt. Looks good, right? But then you press the left arrow key and… ^[[D appears on the screen. WTF is that?

Should I use Turbolinks in Rails?

Sun, 16 Nov 2014 00:00:00 +0000

No. (Don’t believe me? Google it.)

VIM Cheat Sheet

Sat, 15 Nov 2014 00:00:00 +0000

After 9 years of TextMate, I’m switching to vim. I’m writing this cheat sheet as I learn. Check back often.

How to check if Bash is vulnerable to Heartbleed

Wed, 05 Nov 2014 00:00:00 +0000

Run this line in your Bash console: env x='() { :;}; echo vulnerable' bash -c "only this line should appear" If you see this, your Bash is vulnerable to Heartbleed: vulnerable only this line should appear If you see this, your Bash is secure from Heartbleed: only this line should appear

How to programatically control Wordpress with Ruby using XML-RPC

Sun, 02 Nov 2014 00:00:00 +0000

This week, I wanted to programatically create posts on my Wordpress site, Maxims. Unfortunately, all of the example code I found online for controlling Wordpress was using PHP, and I hate PHP. I wanted to control Wordpress with Ruby using XML-RPC.

How to obtain the number of files in a folder, recursively, using Ruby

Sat, 01 Nov 2014 00:00:00 +0000

I have often found myself wanting to know how many files are in a folder, including files in sub-folders. I whipped up a little Ruby code for just that: folder_to_count = "/path/to/folder" # You should change this begin file_count = Dir.glob(File.join(folder_to_count, '**', '*')).select { |file| File.file?(file) }.count rescue puts "ERROR: The number of files could not be obtained" # typically occurs if folder_to_count does not exist end

The location of Postfix's main config file in Linux

Sat, 01 Nov 2014 00:00:00 +0000

On Linux, Postfix’s main configuration file, main.cf, is located at: /etc/postfix/main.cf

Get Safari's Reading List programmatically with Ruby

Sun, 26 Oct 2014 00:00:00 +0000

I wanted to export my Safari Reading List on OS X, so I wrote some code to do it. I leveraged Ruby, but this methodology could be easily ported to other languages like Bash, Python, or Objective C.

How to make a ruby file executable

Sun, 19 Oct 2014 00:00:00 +0000

In the ruby file: #!/usr/bin/env ruby puts 'Hello world' At the command line: chmod +x ruby.rb Then you can execute it like this: ./ruby.rb

CEVA (Amazon) phone number

Sat, 18 Oct 2014 00:00:00 +0000

(800) 592-7489 This is the number for CEVA, the company that delivers oversized / bulk items for Amazon. I wasted 15 minutes trying to find their phone number.

Everything I know about writing for the web in 60 seconds

Thu, 16 Oct 2014 00:00:00 +0000

I used to charge consulting clients thousands of dollars for this knowledge. I no longer consult, so I’m giving away my secrets… for free.

(You’re welcome.)

Toggling two code blocks

Thu, 16 Oct 2014 00:00:00 +0000

Often when debugging code, you toggle between two blocks of code. You comment in one block, and comment out the other block. As simple as it sounds, going back and forth dozens of times can become quite annoying.

How to dump all MySQL databases to a gzip file from inside a bash script

Wed, 12 Mar 2014 00:00:00 +0000

Often as part of an hourly, daily, or weekly server backup bash script, you will wish to dump all MySQL databases to disk as a gzip file. This way, in the case that any of your databases suffer from corruption or user error, you will have a backup. Simply put this command inside your cron-scheduled backup bash script, substituting the USERNAME, PASSWORD, and the destination path with your info: #!/bin/bash mysqldump -u USERNAME -pPASSWORD --all-databases --routines| gzip > /mysqlbackups/MySQLDB_`date '+%m-%d-%Y'`.

The best PGP tutorial for Mac OS X, ever

Wed, 12 Mar 2014 00:00:00 +0000

When I decided to set up my Mac with PGP encrypted communications, I could not believe how hard it was – not just to set up the software, but to understand how to use PGP properly. There was no “PGP for Dummies” tutorial for OS X on the internet. So I decided to write one. This is my über simple, nerd-free tutorial for anyone on Mac. In it, I will:

Cover exactly how to install and configure PGP on OS X
Demonstrate how to use PGP in real life

Creating a ruby launchd task with RVM in OS X

Sun, 02 Mar 2014 00:00:00 +0000

In the last few years, ruby has taken the world by storm. With different projects dependent on different versions of Ruby, many Rails, Jekyll, and Sinatra programmers have installed RVM to manage their ruby versions in OS X. I am one of them.

While RVM is awesome, it can make some previously simple tasks difficult. One such example is creating a launchd daemon that invokes a ruby script. If your gems are installed with RVM, you will need to use RVM to write your daemon. That’s where it gets complicated.

This tutorial teaches you how to schedule a ruby task on OS X using launchd. You can schedule any ruby file to be run. It will be executed using the RVM ruby version of your choice.

How to automatically move downloaded files to your desktop in OS X

Sun, 02 Mar 2014 00:00:00 +0000

Left unchecked, your OS X ~/Downloads folder can grow into a jungle. I solved that problem by setting up an Automator script to move everything from my ~/Downloads folder to my ~/Desktop. Once a day, I clean off my ~/Desktop. This is a quick tutorial how to set your Mac to do the same.

How to populate a select menu with option tags, using jQuery

Sun, 02 Mar 2014 00:00:00 +0000

This code populates a <select> menu with different <option> tags. This code is useful when you wish to change the contents of a HTML dropdown menu programatically.

How to start and stop Apache 2 in Ubuntu Linux

Sun, 02 Mar 2014 00:00:00 +0000

How to start Apache 2: sudo service apache2 start How to stop Apache 2: sudo service apache2 stop How to restart Apache 2: sudo service apache2 restart How to reload Apache 2: sudo service apache2 reload Reloading is useful if you change a virtualhost file, since it will not actually stop Apache. Therefore, your websites will not go offline (even for a few seconds).

In OS X, should I use cron or launchd?

Sun, 02 Mar 2014 00:00:00 +0000

Use launchd. Do not use cron on OS X. Source: the launchd man page.

The percentage of people who are mentally unhealthy

Sun, 02 Mar 2014 00:00:00 +0000

This year I have been conducting research concerning the percentage of mentally unhealthy people for an upcoming project.

I am interested in:

Statistics about America, other countries, and global
Not just mental illnesses (Skitzophrenia, Bipolar disorder, Autism spectrum), but also less several mental unhealth (difficulty holding long-term relationships, not feeling fulfilled, phobias).
The precise definition of mental health and mental illness
Conducting primary research, if necessary

What does the at sign (@) mean in OS X permissions?

Sun, 02 Mar 2014 00:00:00 +0000

If you run ls on a file or folder in OS X…

ls -la /dir/to/some_file_or_folder

You may see a permission entry like this:

-rwxr--r--@ 1 john admins 548 Oct 29 15:58 filename.plist

Where to put custom bash scripts in OS X

Sun, 02 Mar 2014 00:00:00 +0000

If you make a custom bash script in OS X, and you want everyone on the system to be able to access it, this is the directory where you should save it: /usr/local/bin

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