prasanthrp-blog1

[prasanthrp-blog1]

GDB Debugging

For debugger to display the symbols while debugging, we need to build the code with -g flag. 

> gcc -g -o test-pgm test-pgm.c

To start debugger with the program execute on your shell

> gdb test-pgm

To set a breakpoint on function main, execute

> break main

To start the program, execute

> run

The command runs till the break point is hit or the program terminates

To step through execution, run

> step 

Step command steps into functions.

If you don’t want to step into functions, run next command

> next

List next few lines

> list

To exit, run

> quit

Once the program is started you can ask the program to continue running till the next break point by running

> continue

To print the value of a variable i, run

> print i

To display the command continuously run

> display i

To stop displaying variable 

> undisplay i

To finish the current function and then return, run

> finish

To return from the current function without proceeding

> return

To execute a function, call

> call my_function

To see the current stacktrace

> bt

To ignore a signal

> handle SIGSEGV ignore

To see backtrace of all threads

> thread apply all bt

To open a coredump file to debug from shell

> gdb my_program my_coredump

To set watch point, to break execution when the condition is met

> watch i == 10

[prasanthrp-blog1]

Automate ssh to remote server using expect

Expect command is part of tcl/tk tool, which is commonly used for CLI testing automation. Expect command can launch a process and read and write from/to the stdin/stdout. 

For example to login to remote server and execute command we can use the command

#!/usr/bin/expect

set server  [lindex $argv 0] set usr     root set passwd  mypass set cmd [lrange $argv 1 end]

log_user 0

set timeout 10

spawn -noecho ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no  $usr@$server $cmd

expect ".*password:" {    send "$passwd\r"    expect -re ".*\r.*"    log_user 1    expect -re ".*password.*" {        puts "\tERROR:\r"        exit 3    } eof {        catch wait result    }    exit 0 } eof {    log_user 0    puts "\tERROR: \r"    exit 1; }

[prasanthrp-blog1]

How to build vim from code

Vim is one of the favorite editor of most of the programmers. It is always good, to build the vim from source code to get the latest features/fixes without waiting the official release or your office system admin’s mercy.

The procedure is simple and it doesn’t need much expertise.

Download the code from git hub

https://github.com/vim/vim

You can either fetch the code using git or download the zip file directly

Run configure script

./configure --with-features=huge       \            --enable-multibyte         \            --enable-pythoninterp      \            --enable-perlinterp        \            --enable-luainterp         \            --enable-gui=gnome2        \            --enable-cscope            \            --prefix=/home/$USER/usr

Run make to build the binaries

make all 

Install the package to ~/usr/bin directory.

make install