Largely for my own reference, here are some Unix shell tricks that have come up lately. If you’re using Linux, Mac OS X, or other Unix-like systems, these might be handy.

Redirecting output

When a process starts, it opens three file descriptors: file descriptor 0 for standard input (STDIN), file descriptor 1 for standard output (STDOUT), and file descriptor 2 for standard error (STDERR). By default, the standard output and error just print to the terminal (so you see them on the screen), but you can redirect them to a file (e.g. for logging or just to cut down on gibberish that you’re not going to read anyway) by using “>” to create/overwrite the file or “>>” to create/append the file.

I’ve used “find /” as the command in these examples because it takes a while to run and tends to produce plenty of output on STDOUT and STDERR.


# Redirect STDOUT to a file, but leave STDERR to print on screen.
# If the file exists, overwrite it.
$ find / > /some/file.txt
# Redirect STDOUT to a file, but leave STDERR to print on screen.
# If the file exists, append to the end of it. If it doesn't exist, create it.
$ find / >> /some/file.txt
# Redirect STDOUT to the null device, which is a special file that silently discards everything.
# Use this if you want to ignore STDOUT but keep an eye on STDERR.
$ find / > /dev/null
# Redirect both STDOUT and STDERR to the same file.
$ find / > /some/file.txt 2>&1
# Redirect STDOUT and STDERR to different files.
# The numbers refer to the file descriptors mentioned above.
$ find / > /path/to/log.out 2>/path/to/log.err
# ... or, more explicitly:
$ find / 1>/path/to/log.out 2>/path/to/log.err


Background processes

Often you’ll want to start something running and keep working on something else. This is frequently done by redirecting the output to a file (or the null device) by starting it in the background with the “&” keyword.


# Start a process in the background.
$ find / &
# Start a process in the background and ignore all output.
$ find / > /dev/null 2>&1


To bring a background process back to the foreground, for example to stop it with ctrl+c or to provide input if it asks a question, use the “fg” command.

If you start several background processes, use the “jobs” command to list them. That will print the job number (different from the process ID) that you can use to bring a specific one back to the foreground with e.g. “fg 3″ to bring back job 3.


$ find / > /dev/null 2>&1 &
$ cp file.dat /mnt/other_drive &
$ sleep 600 &
$ jobs
[1] Running find / > /dev/null 2>&1 &
[2]- Running cp file.dat /mnt/other_drive &
[3]+ Running sleep 600 &
$ fg 3
sleep 600


Capturing process ID for simple start/stop scripts

Putting those together, here’s a simple start/stop script that starts a command in the background and stores all output in a log file. It also uses the “$!” variable to record the process ID so it can kill the process later. Call the file “startstop.sh” and just run “startstop.sh start” to start it and “startstop.sh stop” to stop it.


#!/bin/sh
PID_FILE="test.pid"
LOG_FILE="test.log"
CMD="find /"
if [ "$1" == "start" ]; then
echo "starting!"
$CMD > $LOG_FILE 2>&1 &
echo $! > $PID_FILE;
fi
if [ "$1" == "stop" ]; then
echo "stopping!"
kill `cat $PID_FILE`;
rm $PID_FILE;
fi


Also note that I’ve put together a 2Paths preferences file that remaps the home and end keys in eclipse, and adds in the 2Paths code formatting templates. To import, once you’ve got the new eclipse up and running, select import and choose preferences.

Download Eclipse 2Paths Edition v2 (155.6MB)

Fix for home and end keys
If you’re anything like me, you are used to having your home and end keys go to the start of the line of text and the end of the line, respectively. The way OS X does it drives me insane, and I’ve finally found a solution that even fixes it in firefox: KeyFixer.

KeyFixer is a free utility that remaps those keys, there are 2 versions, the standard one that remaps it in OS X and most apps, and KeyFixer for Firefox which is self explanatory. I recommend installing them both if you want your home and end keys back.

Download KeyFixer (60KB)

Download KeyFixer for Firefox (80KB)

Eclipse developers will be particularly pleased with the debut of major features and/or specification updates to EJB3 JPA, JSP 2.0, JSF 1.2, Axis2 Web Services, Tomcat support, and source editing. This release also introduces Java EE 5 project support.

I’ve put together a new Eclipse bundle for everyone here at 2Paths. The package includes some useful plugins preinstalled (Subclipse, SpringIDE 2.0., JAutoDoc, and JSEclipse), as well as some performance and stability tweaks.

Download – Eclipse Europa 2Paths Edition (OS X, 155MB)

To ensure everyone is working with the same tools, you should configure your eclipse to automatically check for updates. This can be done by clicking on the Eclipse menu -> Preferences then Install/Update -> Automatic Updates.

If anyone has any problems with this release, just let me know and I can give you a hand getting things sorted out.

First of all, if you haven’t installed this update to the Java SWT libraries from Apple, do it now. It should improve stability with Eclipse.

Download: SWT Compatibility Update (188KB)

Eclipse WTP 1.5.4 is the latest update to the WTP 1.5 line. Not anything new, but contains numerous bug fixes etc.

Download: Eclipse WTP 1.5.4 (183.9MB)

Eclipse WTP 2.0 RC1 is based on Eclipse 3.3 RC1 and appears to be fairly stable. Some of the new features are support for Tomcat 6, support for JPA projects (annotations, , mappings etc), built in support for web services, and spell checking. This is pre-release, so use at your own risk (I’ve been using it and it seems ok, although I keep my 1.5.4 around just incase).

Download: Eclipse WTP 2.0RC1 (227MB)

Remember to update your copy of eclipse regularly to receive the latest bugfixes, or better yet, set it to auto update in preferences.

On a side note, The Daily Grind is a time tracking widget that allows you to track the amount of time you’ve spent on a number of different tasks/projects. It wouldn’t take a lot of work to interface it with JIRA for our time tracking.

Download: 2Paths Blog Widget (584KB)