Checking the JVM Heap Allocation Quickly from the Command Line

One liner for checking the JVM heap memory allocation:

java -server -XX:+UnlockDiagnosticVMOptions -XX:+PrintFlagsFinal -version | grep -i heapsize

On a 32 bit JVM:

uintx ErgoHeapSizeLimit                    = 0                {product}
uintx InitialHeapSize                     := 63763392         {product}
uintx LargePageHeapSizeThreshold           = 134217728        {product}
uintx MaxHeapSize                         := 1020214272       {product}
java version "1.6.0_22"
Java(TM) SE Runtime Environment (build 1.6.0_22-b04)
Java HotSpot(TM) Server VM (build 17.1-b03, mixed mode)

(1 gigabyte allocated)

On a 64 bit JVM:

uintx ErgoHeapSizeLimit                    = 0                {product}
uintx InitialHeapSize                     := 128755328        {product}
uintx LargePageHeapSizeThreshold           = 134217728        {product}
uintx MaxHeapSize                         := 2060085248       {product}
java version "1.6.0_22"
Java(TM) SE Runtime Environment (build 1.6.0_22-b04)
Java HotSpot(TM) 64-Bit Server VM (build 17.1-b03, mixed mode)

(2 gigabytes allocated)

A 32 bit JVM is allocated 1G and a 64 bit JVM is allocated 2G to the max heap space by default.

How to find the Most Recent Commit to a File in Git

As pointed out here, it is pretty simple to find the most recent commit to a particular file in Git:

git log -n 1 -- example/file

Git Diff Filenames Ignoring Whitespace

A colleague of mine asked me whether I knew how to compare 2 branches in Git outputting only the filenames, but ignoring files with only whitespace changes.

Taking inspiration from here, I tried:


git diff --ignore-space-at-eol -b -w --name-only

But I was quite surprised to see files which only had whitespace changes showing up in the output. So I suggested working around the strange Git behaviour like this:


git diff --ignore-space-at-eol -b -w | grep ^diff

Which filters the output of the full diff, giving lines like:


diff --git a/non-whitespace.txt b/non-whitespace.txt
diff --git a/non-whitespace2.txt b/non-whitespace2.txt


He further improved on this by removing the a/ b/ prefix and using awk to extract only the filename for each line:


git diff --ignore-space-at-eol -b -w --no-prefix | grep ^diff | awk '{print $3}'

Giving a nice output:

non-whitespace.txt
non-whitespace2.txt

How To: Create a Bash Terminal in Windows!

Why I Want a Bash Terminal in Windows

Since I have a choice, my favourite operating system for development is Linux and I use it at work. On the other hand, I often want to play computer games in my free time, so I use Windows 7 at home. However, sometimes I like to develop at home so I decided to see if I could add a Linux like terminal to Windows. Why?

I find a Bash terminal is a more compelling command line than trying to use cmd.exe

The skills I have gained from day to day use of Linux are now portable to Windows

I find that being able to open a terminal and perform some operation on the local file system or a remote Linux box using only the keyboard improves my ability to multitask

I understand that there are other ways of dealing with the "Linux for Work, Windows for Fun" problem. I could use a dual boot system or run windows emulation for games at home, but I have tried both of those in the past and they are not to my liking.

A Solution

Install freely available tools MinGW, msys and mintty for a Bash terminal with GNU utilities in Windows. You get familiar tools like: ssh scp cp mv rm ls grep vim wget tar gzip and a Bash terminal!


Warning - This terminal does not like spaces in paths and you will have to perform some workarounds for this for Windows programs you want to be able to invoke from the command line (see "Setup Notepad++" below). Also, these tools do not fully support all Unix functions, but that's OK, the aim here is to make a system which is convenient for developers who work in Linux and Windows rather than creating a full Unix system on top of Windows.

Disclaimer - Another popular solution is Cygwin, a comparison of the two is outside the scope of this blog post, read more here.

MinGW (Minimal GNU for Windows)

Download from here
Choose: mingw-get-inst-20120426.exe
(latest version at the time of writing)

When installing, select Components:

• C Compiler
• MSYS Basic System

Finish installer.

run cmd.exe
Enter following commands:

cd c:\MinGW\bin
mingw-get update
mingw-get upgrade
mingw-get install msys-mintty msys-vim msys-wget msys-openssl msys-openssh msys-tar msys-gzip msys-zip msys-unzip msys-libbz2

Mintty (Xterm Emulator for Windows):

Make a shortcut (link) on desktop for mintty:
name: mintty
path: c:\MinGW\msys\1.0\bin\mintty.exe /bin/bash --login -i

Launch mintty (all terminal commands from this point on are to be entered into mintty)

Mintty Solarized Theme (Optional, but really cool):

Read more about Solarized here

Get from here

Paste the text of light or dark theme into ~/.minttyrc

Also add the lines:

BoldAsFont=no
Font=Consolas
FontHeight=11

Mintty Familiar Behaviour (Optional):

I really miss ll if I don't have it.

Add the following lines to ~/.bash_profile

alias ls='ls --color=always'
alias ll='ls -l'

Move to previous/next word using CTRL+Left/Right Arrow:

Add the following lines to ~/.inputrc

# Ctrl+Left/Right to move by whole words
"\e[1;5C": forward-word
"\e[1;5D": backward-word

Exit and open a new terminal to check that these work.

Customise Vim (Optional):

I added syntax highlighting, tabs for spaces and set paste and a mode dependent cursor to vimrc:

vim /share/vim/vimrc

" Syntax highlighting on
syntax on

" Allow pasting blocks of code
set paste

" Tabs for spaces
set expandtab
set tabstop=4

" Mode dependent cursor
let &t_ti.="\e[1 q"
let &t_SI.="\e[5 q"
let &t_EI.="\e[1 q"
let &t_te.="\e[0 q"

Msysgit (Git for Windows):

If msysgit is already installed on your system, remove it first, we need to install it again in a non-default directory.

Download from here

Choose: Git-1.8.1.2-preview20130201.exe
(latest version at the time of writing)

Msysgit installation path: C:\msysgit

Configuring the line ending conversions
Checkout as-is, commit Unix-style line endings

Add c:\msysgit\cmd to the PATH env variable

(Start bar -> run "Edit System Environmental Variables" -> Environmental Variables ->Edit PATH variable)

Git Colour (Optional):

vim /c/Users/[username]/.gitconfig

http://nathanhoad.net/how-to-colours-in-git

Set up Notepad++ (Optional):

Notepad++ is a pretty cool text editor, in fact, I would not mind having this program in a Linux environment. However, MinGW does not like spaces in paths (e.g. C:\Program Files (x86)\Notepad++\ ). So to access Notepad++ from mintty, it is necessary to uninstall Notepad++ and reinstall to a directory not containing a space for example: C:\Notepad++

Once this is done, add C:\Notepad++ to the PATH env variable

(Start bar -> run "Edit System Environmental Variables" -> Environmental Variables ->Edit PATH variable)

(Optional again) Make a shortcut for Notepad++ with fewer characters:

cd /c/Notepad++/
ln -s notepad++.exe np

Then edit a text file from anywhere in mintty like:

np my.xml

However, Windows 7 does not allow its users to set the default for opening a particular file type to an executable which is outside one of the 'Program Files' folders. This might trouble you if you want Notepad++ to be the default .txt, .xml etc. editor. MinGW doesn't like spaces in paths so let's do a workaround!

The workaround for this is to add a .bat file (Windows version of a shell script) in a folder contained in the Program Files folder. Start off by creating the directory:

C:\Program Files\Shortcuts
(You may prefer C:\Program Files\AAShortcuts as it will be at the top of the list)

Create a file inside that directory called notepad++.bat and add the line:

start notepad++ %*

This starts Notepad++ (which is on the PATH) in a new window and forward the arguments given to the script.

Then you can set the default application for the desired file type (e.g. .xml) as normal
Shift+Right Click on an .xml file -> Choose Default Program -> Browse to:

C:\Program Files\Shortcuts\notepad++.bat

Notepad++ Solarized Theme (Optional):

Notepad++ has Solarized theme built in:

Settings -> Style Configurator -> Select Theme -> Solarized

For a consistent theme with the terminal:

Font name: Consolas
Font size: 11

Save & Close

How to Get the Absolute Path of the Currently Executing Script

Assign the directory of the currently executing script to a variable and then print it to the standard out:

pushd `dirname $0` > /dev/null
PATH_TO_SCRIPT=`pwd -P`popd > /dev/null
echo "Path:" $PATH_TO_SCRIPT;

Explanation:

1. Move to the directory of the script

2. Assign PATH_TO_SCRIPT to the absolute path of the current directory resolving symbolic links

3. Move back to the original directory

4. Print out the path