Tech Trek

Find lines of code in your repository

2009-11-07T09:23:00.004+05:30


        for ext in "*.java" "*.xml" "*.css" "*.jsp" "*.js" "*.sql"
        do
                echo -n "$ext,$location,"
                find ./$location -iname "$ext" -exec wc -l '{}' \;|gawk '{total+=$1} END{print total}'
        done

Passing Debug Parameters to JVM using Ant

2009-10-22T17:54:00.001+05:30

Getting tablespace Size

2009-07-02T19:20:00.000+05:30


SELECT tablespace_name,
       SUM (bytes) / 1024 / 1024 current_size,
       autoextensible,
       SUM (maxbytes) / 1024 / 1024 max_size
FROM dba_data_files
WHERE tablespace_name like '%'
GROUP BY tablespace_name, autoextensible
ORDER BY 1

bash : search and replace from previous command

2009-05-10T14:53:00.002+05:30

tar -cvf sandeep.tar sandeep/

!!:gs/sandeep/singhal will mean

tar -cvf singhal.tar singhal/

:gs is for global search and replace

bash - last argument of the previous command (nth argument)

2009-05-10T14:19:00.004+05:30

Get the last argument of the previous command : !!$
Get the first argumnet of the previous command : !!^
Get the 1st argument of the previous command : !!1
Get the nth argument of the previous command : !!n

Examples :

$> ls :!!$ (or !$)

$> ls :!!^

$> ls :!!2

$> ls :!!n

Trigger GC in eclipse.

2009-05-02T12:12:00.003+05:30

This is a handy for eclipse which lets you to trigger gc in the eclipse instead of waiting for the jvm to schedule the GC .

Go to Window->Preferences->General, mark Show Heap status check box.
The current Heap usage with icon for "Run Garbage Collector" will appear at the bottom right.

It helps a lot in eclipse performance.

I find it pretty handy especially because I do not shutdown eclipse often.

Two things I love about opera

2009-05-01T09:51:00.003+05:30

1. You can type windows specific path on the browser bar and it will covert it to "forward slashes" when you are browsing directory like strucure on a browser

2. The quick search box : The cursor remains at the same place if you go to a different window by "ALT-TAB". This in firefox changes to select the entire text already typed in the search box. Hence you cannot start typing straight away, since that will erase the already entered text.

Common sqlplus commands

2009-04-26T21:01:00.000+05:30

ACCEPT - Get input from the user
DEFINE - Declare a variable (short: DEF)
DESCRIBE - Lists the attributes of tables and other objects (short: DESC)
EDIT - Places you in an editor so you can edit a SQL command (short: ED)
EXIT or QUIT - Disconnect from the database and terminate SQL*Plus
GET - Retrieves a SQL file and places it into the SQL buffer
HOST - Issue an operating system command (short: !)
LIST - Displays the last command executed/ command in the SQL buffer (short: L)
PROMPT - Display a text string on the screen. Eg prompt Hello World!!!
RUN - List and Run the command stored in the SQL buffer (short: /)
SAVE - Saves command in the SQL buffer to a file. Eg "save x" will create a script file called x.sql
SET - Modify the SQL*Plus environment eg. SET PAGESIZE 23
SHOW - Show environment settings (short: SHO). Eg SHOW ALL, SHO PAGESIZE etc.
SPOOL - Send output to a file. Eg "spool x" will save STDOUT to a file called x.lst
START - Run a SQL script file (short: @)

source :

http://www.orafaq.com/wiki/SQL*Plus_FAQ

Oracle - Default Location for data files

2009-04-20T13:54:00.001+05:30

To get the existing location

sql > show parameter db_create;

To set a new location

sql> alter system set db_create_file_dest='/home/ssinghal/oradata';

Vim - Reduce Backslashing

2009-04-08T13:59:00.001+05:30



Appending a "\v" reduces the amount of backslashing the search expressions.

/codes\(\n\|\s\)*where : normal regexp
/\vcodes(\n|\s)*where  : very magic

source :
http://vim.wikia.com/wiki/Best_Vim_Tips

Vim - Open Current File in Explorer or Command Prompt

2009-04-07T14:04:00.004+05:30

Put the following two lines in your vimrc files under window to get F11 and F12 to work as "command prompt here" and "explorer here" !


map  :silent !start cmd.exe /k pushd %:p:h
map  :silent !start explorer.exe %:p:h

source for tip1

"http://vim.wikia.com/wiki/Open_the_folder_containing_the_currently_open_file"

source for tip2

A variant of tip 1 using windows trick of adding a registry for folders to open a command prompt

Note : % represents the file open in current buffer

Oracle dba_jobs : Breaking

2009-04-06T13:57:00.002+05:30

exec dbms_job.broken(690,true);

where 690 is the job number obtained from
select * from dba_jobs

Oracle databases - startup and shutdown

2009-04-06T13:54:00.004+05:30

Shutdown:

$ export ORACLE_SID=db_sid
$ sqlplus /nolog
sql> connect / as sysdba
sql> shutdown immediate

Startup :

$ export ORACLE_SID=db_sid
$ sqlplus /nolog
sql> connect / as sysdba
sql> startup mount
sql> alter database open;

Note: This needs to be done by logging on the machine where oracle database is installed

marks in vim - bookmarks

2009-02-24T18:58:00.000+05:30

- Go to a line where you want a mark and press mx - this will create a bookmark

( x can be any alphabet from a-z)

- Now navigate away from that place. If you need to get back to the earlier cursor location press "`x" (back-tick and x)

- You can set multiple "marks" in a single file and navigate using back-tick and the alphabet used to create a mark

Cron entry for other users

2009-02-16T16:13:00.000+05:30

Execute the following as root :

cat /var/spool/cron/ssinghal

where ssinghal is the user name

Sed - Deleting lines matching a pattern

2009-02-06T11:36:00.002+05:30

sed -i '/.*log$/d' file_names.txt

Deletes all the lines ending with "log" from the file "file_names.txt"

marks in vim - bookmarks

2009-01-27T08:29:00.002+05:30

Go to a line where you want a mark and press mx - this will create a bookmark

( x can be any alphabet from a-z)

- Now navigate away from that place. If you need to get back to the earlier cursor location press "`x" (back-tick and x)

- You can set multiple "marks" in a single file and navigate using back-tick and the alphabet used to create a mark

sed : inplace replacement

2009-01-26T21:39:00.004+05:30

It is easy to open a file in vim and do a search replace - but if the file runs into huge sizes, a regular editor would not be able to perform search and replace tasks on it efficiently. For these situation, you need a "stream" editor. Here is an example for replacing "foo" with "bar" in a file called snafu.txt

sed -i -e 's/foo/bar/g' snafu.txt

Where:

-i : Is for inplace replacement

-e: sed script to be run on the file

samba mount

2009-01-26T21:21:00.001+05:30

Using samba to mount a windows shared folder

mount -t cifs -o username=Home\\sandeep //192.168.0.1/Shared/ /media/Shared

Where /media/Shared is the target folder where the network folder will be mounted.

Executing a command remotely using ssh

2009-01-25T18:49:00.001+05:30

Following command will run a shell script on a remote machine

ssh ssinghal@192.168.0.1 /tomcat/jakarta/bin/kill.sh

Capturing output of terminal on Unix

2008-12-26T12:31:00.002+05:30

Terminals do not have a great scroll length and even though you can increase the number of lines that can be scrolled up, it is always useful to have the output captured in a file so that you can search on it. Here are few ways

1. Redirection

cat foo.txt > bar.txt

Outout of foo.txt is captured in bar.txt

2. Redirection with "append"

ls >> bar.txt

This will append the output of "ls" to bar.txt ( Instead of overwriting it)

3. "tee"
Redirect and redirect with append will not display the content on console and hence if you want to see the content and also redirect it to a file , use "tee"

ls | tee bar.txt

this will display the contents of ls on terminal and also redirect it to bar.txt

4. output to multiple files

ls | tee a.txt b.txt c.txt

This will output contents of ls to a.txt, b.txt, c.txt

5. Outout all the terminal interaction to a file

script -f out.txt

Converting UTF-16 to UTF-8

2008-12-22T08:57:00.003+05:30

I was running grep on an xml file (big one) and realized that it did not match the pattern I was expecting the the file. I then did a "head" from the file to see a pattern that is present in it. Grepping on that too returned nothing telling me that grep is somehow not working on this file.
"head" was returning some junk characters at the begining of the file - This idicated that the file does not have a normal text encoding and probably that is the reason why grep is not working on it.
Reading the XML header proved that, since it was "UTF-18", grep was not running over it. I had to convert the file to UTF-8 which is more text friendly if the content is only English.

iconv --from-code UTF-16 --to-code UTF-8 input_file.xml > output_file.xml

screen

2008-12-13T21:14:00.001+05:30

when to I use screen :

* When "nohup" is just not enough
* When the power goes off and you are left in the middle of nowhere
* When I need to log on to 10 different terminals each day
* When I do not want to enter 10 different username passwords each day

"screen" is a terrific unix utility that allows you to start a terminal without having to worry about you job being interreputed mid-way. It is better than nohup in that respect nohup only allows unix commands to be started in a "nohup" fashion. If for instance you are working with an interactive program like sqlplus and your internet connection happen to break, you will loose your context and any transactions that you were working on.

It essentially allows you following :
* Multiple sessions in a single ssh window (screen multiplexing)
* Ability to "resume" a session in the state you left it - irrespective of power outage, internet connection termination etc

Here is how you use it :

1. Make sure it is installed on your system by typing "screen --help"
2. If it is not installed, you can install it by "yum install screen" on a fedora box.
3. start a screen session by typing "screen" and you should be in a screen session.
4. If you are disconnected or closed the terminal, type "screen -r -d" to reattach to the session

Here are some of the short-cuts available (All after CTRL+A)

c : creates a new
n : next screen window
p : previous screen window
a : toggle between two screen windows
[0-9] : Go to a specific screen window identified by a number
A : Set the name of a screen window
" : List all the existing screen
ESC : Scroll up or down on a screen

Man on the moon (well almost)

2008-11-15T11:03:00.003+05:30

India becomes the 4th Nation to put a lunar probe on the moon ! I am proud to be the 4th country to do that(as against the alleged 3rd world country banter from Matthew Hayden who knows nothing more than being a sore loser)

pasting code in vim

2008-10-19T09:18:00.002+05:30

:set paste

paste the code

:set nopaste

set pastetoggle=F3 in your vimrc file is an alternative.