An apple a day

Bash : find days in previous month

ranjithchandran — Mon, 29 Mar 2010 15:59:45 +0000

Here is a one liner to find the number of days in previous month (works in bash and KSH)

cal $((`date '+%m'`-1)) `date '+%Y'` | grep . | fmt -1 | tail -1

Find sum of file sizes listed in ls -l using awk

ranjithchandran — Mon, 01 Mar 2010 21:17:01 +0000

ls -l | awk '{ TOTAL += $5} END { print TOTAL/1024/1024 }'

With this, awk will pull field number 5 from ls -l, which is the size in bytes in most of the *nix platforms.

Then for each occurrence add to the variable TOTAL. At “END”, it will divide TOTAL by 1024*1024 ( bytes to MB) and print

Shell script to read java-style property files

ranjithchandran — Thu, 28 Jan 2010 21:08:49 +0000

One interesting API in Java is to manipulate key-value configuration files known as ‘properties’

I do not know if shell script gurus like to use property files. However, if you are looking for some code to read a key-value pair property file, here is something:

#!/bin/sh
#---------------------
# arg1: prop file
# arg2: prop key
# returns property value if found,
# nothing if not found
#---------------------
get_prop(){
propfile=$1
key=$2
grep  "^${2}=" ${1}| sed "s%${2}=\(.*\)%\1%"
}

Suppose you have a properties file such as : test.properties below

user.name=Ranjith
init.dir=/tmp

A test call to get value for “user.name” would look like

get_prop test.properties user.name

Printing a crude boxed message using perl – useful in shell too

ranjithchandran — Tue, 08 Dec 2009 16:13:26 +0000

Sometimes you would want to print boxed messages such as the following from a script:
+-----------------------------------+ |A word is defined as a string of | |characters delimited by spaces, | |tabs, or newline characters. | +-----------------------------------+

If you want to have a re-usable routine to do this, things get a bit complex. There comes print formatting and word wrapping. While print formatting is easy in shell with printf, word wrapping would require writing a lot of lines of code and trickery. But you can do this real quick using Perl. Here is a little program.
To execute, pass string to be boxed and width of the box as commandline arguments as below

 perl box.pl "A word is defined as a string of characters delimited by spaces, tabs, or newline characters." 35

Source:

use Text::Wrap;
$Text::Wrap::columns = $ARGV[1];
print ( "+" . ( "-" x $ARGV[1] ) . "+\n" );
foreach(split('\n',wrap('', '', $ARGV[0])))
{
        printf "|%-$ARGV[1]s|\n", $_;
}
print ( "+" . ( "-" x $ARGV[1] ) . "+\n" );

Shameless plug

ranjithchandran — Sat, 05 Dec 2009 02:43:34 +0000

Here is my Google project to demo hibernate search features.
http://code.google.com/p/hb-search-demo/

Quick find and edit using vi in Linux/UNIX

ranjithchandran — Tue, 17 Nov 2009 16:04:39 +0000

OK, so you want to edit/view all the files matching certain pattern on vi from command prompt. How would you do it?
Search files using usual “find” command, then translate new line in result to space using “tr” command and feed the list to vi – simple! Here you go:

vi `find . -name *.sh  | tr '\n' ' '`

Scala does not have checked exceptions

ranjithchandran — Fri, 31 Jul 2009 08:46:15 +0000

Good! so, the following code will not impact your method signature

def doSomething(n:Int) = {
  if (n < 10) {
    throw new  Exception("Only values between 1 and 10")
  }
 ...

vim 7 spell check

ranjithchandran — Wed, 29 Jul 2009 05:39:06 +0000

vim as of version 7 had introduced built-in spellchecker. I had not used till date, but recently checked it out. So, to turn it on, type command
set spell
If you have some text on your vim and you turn sell on with above command, you will see red underlines for words that vim thinks are incorrectly spelled. Of course, while coding you might not want spell check, so you can turn it off by
set nospell
Now, about navigation and correction.
To go to next spelling error, the keyboard command is ]s to go to previous error, the command is [s. To see spelling suggestions, while the cursor is on word with error, press =z and it presents a list of possible words to choose from. Just type the number corresponding to the word that you are interested in, and you are all set.

Java Generics puzzler

ranjithchandran — Mon, 20 Jul 2009 09:22:04 +0000

Ok, so you are very excited about Generics and would “Generify” whatever you can. But here some interesting pointers.

One: This will cause a compilation error


 Set set = new HashSet();
 set.add("Testing");
 set.add("Testing again");
 set.add("Testing again and again");
 set.add(new Integer(1));

Okay, that we all know.

Two: Now, what will happen with this?


  public static void main(String[] args){
    Set set = new HashSet();
     set.add("Testing");
     set.add("Testing again");
     set.add("Testing again and again");
     doSomething(set);
     System.out.println(set);
   }
   private static void doSomething(Set s){
     s.add(new Integer(21));
   }
}

This will compile fine (With a warning actually, that we all would ignore) and print contents of the set, including a number.

Three: Well, how to fix this ? How to throw an error when a legacy code is attempting to change the sole purpose of your HashSet? The answer is to declare your set as

Set set = Collections.checkedSet(new HashSet(),String.class);

If you want to add an Object to java.util.TreeSet, it must implement Comparable

ranjithchandran — Fri, 17 Jul 2009 09:39:51 +0000

public class Employee{
  private String name;
  Employee(String str ){
    this.name= str;
  }
}
public class Test {
  public static void main(String argv[]){
    TreeSet myMap = new TreeSet();
    Employee s3 = new Employee("abcdef");
    Employee s4 = new Employee("abcdef");
    myMap.add(s3);
    myMap.add(s4);

This code will throw a
Exception in thread "main" java.lang.ClassCastException

Unless Employee implements comparable