Bash: create alias

If you find yourself repeatedly running a wordy command, having to look up how to run a command, or forgetting a username and password combination, I suggest looking into creating a bash alias.

To create a bash alias, do the following:

1. Start up terminal

2. Type cd ~  to go to your home folder

3. Type touch .bash_profile to create the new file

4. Type vim .bash_profile or open this file in your favorite editor.

5. Add your alias by adding a line to this file in the format alias <alias name>='<command>’ . For example alias gw=’./gradlew’.  This will create an alias named gw , which when typed will run the command ./gradlew  from wherever gw  is typed.

6. Type . .bash_profile  to reload your bash profile which loads any newly added aliases.

At this point you can type your alias instead of the wordy command you had been previously typing.

java.net.BindException: Address already in use:8080

Address already in use, BindException

If you’ve ever encountered this exception:
java.net.BindException: Address already in use:8080
there’s a great tool that you can use to determine what application(s) are running on a specific port: lsof

Looking at the man page for lsof, we find the following:


DESCRIPTION
Lsof revision 4.81 lists on its standard output file information about files opened by processes for the following UNIX dialects:

AIX 5.3
FreeBSD 4.9 for x86-based systems
FreeBSD 7.0 and 8.0 for AMD64-based systems
Linux 2.1.72 and above for x86-based systems
Solaris 9 and 10

(See the DISTRIBUTION section of this manual page for information on how to obtain the latest lsof revision.)

An open file may be a regular file, a directory, a block special file, a character special file, an executing text reference, a library, a stream or a network file (Internet socket, NFS file or UNIX domain socket.) A specific file or all the files in a file system may be selected by path.

Instead of a formatted display, lsof will produce output that can be parsed by other programs. See the -F, option description, and the OUT-PUT FOR OTHER PROGRAMS section for more information.

In addition to producing a single output list, lsof will run in repeat mode. In repeat mode it will produce output, delay, then repeat the output operation until stopped with an interrupt or quit signal. See the +|-r [t[m<fmt>]] option description for more information.


To use it, type the following:
lsof -i:<port>
So in our case, we attempt to bind to port 8080, so running:
lsof -i:8080
Gives us an output like the following:

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
MyApp 50845 dustinkendall … … … … … …

To kill the process, type:
kill <pid>
So in our case:
kill 50845
This will help you get past the java.net.BindException and allow you to bind to that port.

How to Add a Private Key to Your Mac OS X Keychain

Add a Private Key to Your Mac OS X Keychain

If you are using Mac OS X, you can add a private key to the built-in keychain by typing the following:

Oftentimes your ssh key is named id_rsa and is stored at ~/.ssh. To add this file to your keychain do the following:

Whenever you boot/reboot your Mac, all SSH keys in your keychain will be automatically loaded.

You should be able to see the keys from the command line via:

Hope this helps!

6 tips for better interviewing for Software Engineers

A few weeks ago a good friend of mine interviewed for a Software Engineering position on my team. We have a very high bar when it comes to interviewing — our interview sessions usually include a lot of whiteboarding and tough programming problems. We didn’t end up making my friend an offer, and a few days later he texted me asking for advice that I could give him that he could use to improve his interviewing skills. Here’s what I ended up sending him:

1. Pick 5 hard problems, and know them well. I would suggest starting with 5 good programming problems, maybe even problems you heard while interviewing here or others you’ve come across. Make sure you understand the problem very well. Spend time thinking about the problem.

2. Practice in an environment that simulates the interview setting. Grab a friend and have her/him ask you questions that you’ve prepared in advance, and allow them to ask their own questions. Practice in front of a whiteboard, if possible in a meeting room or office, to simulate a real interview. Envision in your mind being at an actual interview, at the company you plan on interviewing with.

3. Restate the problem to the interviewer, and make sure that they know that you understand the problem. Part of this may be repeating or restating the question back to the interviewer. Doing this shows that you can communicate well. It also helps make sure that you are sure of what they are asking. At this point you want to clarify any assumptions you are making before you move forward. Getting an assumption cleared up or removed will help you tremendously — if they aren’t cleared up you can end up in left field real fast, solving a problem that is either not the problem the interviewer had in mind or is considerably harder than what was originally asked. If you clear up assumptions, you make the problem set very clear in your mind, and more often than not the problem becomes easier than it might have been.

4. Don’t ‘sign off’ too early. What I mean by this is many times interviewees tell the interviewer that they are done with their solution, when they haven’t double checked their work. When you feel you are done, take a deep breath and run through your code a couple of times. Test your code (see point 5). Don’t be too eager to be done with your solution. You’ll appear much better if you relax and take a second to revise and thoroughly inspect your code. You most likely have a problem that you’re not seeing. Fix the problem and repeat this process.

5. Test your code. In particular, boundary conditions. For example, if the problem being asked involved operations on a list, I would make sure that test cases I run through included lists with the following properties: null list, empty list, list with 1 item, list with a many items (or maximum depending on implementation/structure), list with mixture of null and non-null items, etc.

6. Think about memory and big O. More often than not, I’ll ask the interviewee, “Is there any way you can make this algorithm more efficient?” What I’m looking for is an understanding from you that you know there are tradeoffs of time and space when designing an algorithm. Can you reduce the amount of memory your solution uses? Can you improve the time complexity. What is the time complexity of your algorithm? Be prepared to answer these questions. Bonus: take a look at Wirth’s law and understand its implications.

Conclusion

These are just a few of the observations I’ve made while interviewing Software Engineers. Do you have any to add? Leave your suggestions in the comments below.