Search And View

Simple script for searching a file and viewing it in one go:



#!/bin/bash

usage="$0 "
if [[ $# -ne 1 ]];then
echo $usage
exit 1
fi
files=`find . -name "$1";`
if [[ -z $files ]];then
echo "$1 not found"
fi
count=0
for f in $files; do
((count += 1))
done
echo "Found $count files matching $1"

for f in $files; do
echo $f
echo -n "Enter [Open : y , quit : q , skip : any other char] "
read ans
if [[ $ans == "q" ]];then
break;
fi
if [[ $ans == "y" ]];then
vim $f
break;
fi
done

Making cygwin work

You usually try to recreate the environment that you are most comforatable with. So when I got my work laptop, one of the first things I did was to install cygwin. Now cygwin works pretty well for the most part, however its a disaster when converting between windows style and unix style of file paths. Then of course you discover cygpath command which does exactly that.

Classpath for JAVA:

However this does not fix you java classpath issues. I struggled with this for a long time till I found this: just make sure that the path separator is ";" and put a double quote around the classpath :

cygwin > java -cp ".;./classpathdir/;dir" Test

Using Console for cygwin

If you have cygwin on the windows cmd console, then its time to switch to console (Yes its console, though I wish they could have dreamt up a better term just to avoid any confusion.) Its available at http://sourceforge.net/projects/console/. It's pretty lets you do multiple tabs , unlimited resizing etc. Best of all you can set cygwin bash as your default shell !!




Use SSH instead of Putty

If you have made is so far, why not open ssh instead of putty. Don't get me wrong. I love putty myself, however it doesn't have tabs (well it does but you have to download putty manager for that). You get the advantage of multiple tabs, plus you can script your access now. (Note: cygwin will not download openssh by default, you need to download it). If you use password less access to your servers, you can use ssh-agent to cache your keys in memory. I have a function in my .bashrc that I just run to cache the keys:


alias keyon='ssh-add /cygdrive/c/Documents\ and\ Settings/user/My\ Documents/PrivateKeys/id_rsa'
alias keyoff='ssh-add -D'
alias keylist='ssh-add -l'

function ssh_agent_start
{
SSHAGENT=/bin/ssh-agent
if [[ ! -a $SSHAGENT ]]; then
echo "SSHAGENT not found $SSHAGENT"
return
fi
echo Starting SSH-agent
SSHAGENTARGS="-s"
if [ -n "$SSH_AUTH_SOCK" ]; then
echo "Killing existing agent"
eval `$SSHAGENT -k`
fi
eval `$SSHAGENT $SSHAGENTARGS`
trap "kill $SSH_AGENT_PID" 0
keyon
}

Now you can easliy login to your favourite server without password:
> ssh_agent_start
> ssh user@myserver

Can you sudo ?

One of the big improvements that ubuntu has over other distributions is that it disables root account by default. So every time you have to do something as root, you have to run it as sudo. This by no means is an replacement to the man page, but some things that I found useful.

1. To change sudo prefs, try visudo. Don't edit sudoers manually, as visudo makes sure that the syntax checks out before you save.
2. To change default timeout try:
Defaults:your_user_name timstamp_timeout=7200
3. Other than that the file is pretty well self documented.

I am an avid vim user.  I cannot compare it to emacs, as I have rarely used emacs because of its werird keyboard sequence.  Anyway its important to carry around your vimenv with you.  I am posting below my .vimrc file.  In addition, I have had to add the following extensions to make it do my bidding:

1. vimshell : Vim  has had buffers for a few versions. But it does not support shell access in any of its buffers. Enter vimshell. Its extremely convenient when debugging your code. Thing is you have to patch the vim code and recompile it. But its totally worth it.

2. matchit.vim plugin: google it. Its lets you to match on html/xml tags as well Super userful

-------------------------vimrc----------------------------------------------

"type :help option to get help on options below

set tags=tags;/

set nocompatible

set backspace=2

set confirm

set dictionary=/usr/share/dict/words

set formatoptions=tcq2

set incsearch

set listchars=tab:»·,trail:·

set report=1

set shortmess=fnrxotTI

set smarttab

set textwidth=78

set title

set whichwrap=

set wildmenu

set tabstop=2

set shiftwidth=2

set expandtab

set paste

set ruler

set incsearch  " do incremental searching

set history=50

set hlsearch

"set viminfo='20,\"50  " read/write a .viminfo file, don't store more

      " than 50 lines of registers

set viminfo='10,\"100,:20,%,n~/.viminfo

au BufReadPost * if line("'\"") > 0|if line("'\"") <= line("$")|exe("norm '\"")|else|exe "norm $"|endif|endif

filetype plugin on

syntax on

function CodePrefs()

    set cindent

    set cinoptions=(0,u0

    set expandtab

    set makeprg=gmake

    set shiftwidth=4

    set textwidth=0

endfun

if has("autocmd")

    autocmd FileType c,cpp,html,make,perl,php,php3,php4,inc,sh,dc call CodePrefs()

    autocmd FileType make set noexpandtab nosmarttab

    autocmd FileType mail set textwidth=72 titleold=mutt

    autocmd FileType html set shiftwidth=2

endif

" Transparent editing of gpg encrypted files.

" By Wouter Hanegraaff

augroup encrypted

    au!

    " First make sure nothing is written to ~/.viminfo while editing

    " an encrypted file.

    autocmd BufReadPre,FileReadPre      *.gpg set viminfo=

    " We don't want a swap file, as it writes unencrypted data to disk

    autocmd BufReadPre,FileReadPre      *.gpg set noswapfile

    " Switch to binary mode to read the encrypted file

    autocmd BufReadPre,FileReadPre      *.gpg set bin

    autocmd BufReadPre,FileReadPre      *.gpg let ch_save = &ch|set ch=2

    autocmd BufReadPost,FileReadPost    *.gpg '[,']!gpg --decrypt -q -a 2>/dev/null

    " Switch to normal mode for editing

    autocmd BufReadPost,FileReadPost    *.gpg set nobin

    autocmd BufReadPost,FileReadPost    *.gpg let &ch = ch_save|unlet ch_save

    autocmd BufReadPost,FileReadPost    *.gpg execute ":doautocmd BufReadPost " . expand("%:r")

    " Convert all text to encrypted text before writing

    autocmd BufWritePre,FileWritePre    *.gpg   '[,']!gpg --encrypt --default-recipient "Punit Rathore " -q -a 2>/dev/null

    " Undo the encryption so we are back in the normal text, directly

    " after the file has been written.

    autocmd BufWritePost,FileWritePost    *.gpg   u

augroup END

Automate tedious tasks using Autoit

One of my collegues was looking for a script that would let him automate his daily ritual of opening up 4-5 putty sessions to his linux host. I had used autoit before and suggested it to him. I hadn't used it in a while and was curious as to how it worked. After downloading it took me all of 45 minutes to come up with the following script. It asks for your password, then uses it to log on to 5 different putty sessions!!

---------------------------------------------------

; this script logs you on to 5 different putty sessions

$answer =  InputBox ("enter password", "please enter your password","","*",150,80)

If $answer = "" Then

MsgBox(0, "AutoIt Example", "Enter valid password")

Exit

EndIf

Opt("WinTitleMatchMode", 2)

For $count = 1 To 5

Run("C:\Program Files\PuTTY\putty.exe -ssh username@hostname")

WinWaitActive("PuTTY")

Sleep(1500) 

;MsgBox(0,"Sending password" ,$answer)

Send($answer)

Send("{ENTER}")

Next

--------------------------------------------------------------

Traps in printf

I was debugging this segmentation fault that we were seeing at a customer. It wasn't caught because in never hit the code path in dev/QA. It would happen when logging was enabled. GNU debugger seemed to indicate that the logging library was using the vnsprintf call which uses va_list (variable argument list) as input. I spent close to 2 hrs trying to debug this before realizing the error. So lets see if you can try to figure it out. The same problem exists in printf as well:

printf(" some randmon long %l and string %s \n", 4, "hello");

compile the above and it will throw segv.

Thing is, its easy to assume that %l is a specifier for long. Its not. Its a length specifier not type specifier. You have use %ld. In absense of that printf will assumen that the first arguement ( 4) is a string and throw segv.

Lesson: variable arugement is very powerful. but be aware of the traps.

The case of missing core dumps

Have you had situations when your program seg faulted and yet did not create a core file. Well run the following commad :

> ulimit -a

if you see "core file size  0" then there's your answer.

To enable run the follwoing :

> ulimit -c unlimited

viola.