Unix Internals - With C Programming Examples-2

Print all the environment variables using the envp argument in main() function.

/* Program to Print Environment Variables * Program Name : prenv.c * */ #include <stdio.h> int main(int argc, char *argv[], char *envp[]) { int i = 0; while (envp[i]) { printf("Environment Variable : %s\n", envp[i]); i++; } return 0; }

Print all the environment variables using extern variable environ.

/* Program to Print Environment Variables * Program Name : prenvv.c * */ #include <stdio.h> extern char **environ; int main(int argc, char *argv[]) { int i = 0; while (environ[i]) { printf("Environment Variable : %s\n", environ[i]); i++; } return 0; }

The output of both the programs are same.

Program Output:

$ ./prenv Environment Variable : _=./prenv Environment Variable : HZ=100 Environment Variable : SSH_TTY=/dev/ttyp0 Environment Variable : PATH=/bin:/usr/bin:/usr/gnu/bin:/sbin:/usr/local/bin Environment Variable : HUSHLOGIN=FALSE Environment Variable : EDITOR=emacs Environment Variable : SHELL=/bin/ksh Environment Variable : HOME=/home/reemus Environment Variable : TERM=xterm Environment Variable : PWD=/home/reemus/prog/cprog Environment Variable : TZ=EST5EDT Environment Variable : ENV=/home/reemus/.kshrc $

Unix Internals - With C Programming Examples-1

For a long time I wanted to create a series of Blog post of what I have learned as Unix System Programming and its Internals with the help of plain simple to read examples.

Program: cmdargs.c

/* Program to read and display the command-line arguments */ #include <stdio.h> int main(int argc, char *argv[]) /* argc - No. of Command-line Arguments passed to the program */ /* argv - Array of Strings - Command-line Arguments */ { int i; printf("No. of Command-line Arguments : %d\n", argc); for (i = 0; i < argc; i++) { printf("Arg[%d] = %s\n", i, argv[i]); } return 0; }

Output:

$ ./cmdargs one two three No. of Command-line Arguments : 4 Arg[0] = ./cmdargs Arg[1] = one Arg[2] = two Arg[3] = three $

As you can see the "argc" contains the number of command-line arguments passed to the program.

The very first command-line argument for the program is program name itself, followed by the other arguments passed.

Books for Programmers (From Quora)

Books to be Read by Programmers

1. Gödel Escher Bach by Douglas Hofstadter (cognitive scientist)
2. The Metamagical Themas by Douglas Hofstadter
3. The Art of Computer Programming by Donald Knuth
4. Causality: Models, Reasoning and Inference by Judea Pearl
5. Concepts, Techniques, and Models of Computer Programming by Peter Van Roy
6. Purely Functional Data Structures by Okasaki
7. The Art of Meta Object Protocol by Gregor Kiczales
8. To Mock a Mockingbird by Raymond Smullyan

UltraEdit Compile And Execute Batch Files

Compile Batch File

@echo off

set FULL_FILENAME=%~1
set FILENAME=%~n1
set DIRNAME=%~dp1
set FILE_EXT=%~x1

echo Full File Name: %FULL_FILENAME%
echo File Name: %FILENAME%
echo File Directory: %DIRNAME%
echo File Extension: %FILE_EXT%

set CC_BIN=gcc
set CPP_BIN=g++
set GHC_BIN=ghc
set SCALA_BIN=scalac.bat

set CC_EXT=.c
set CPP_EXT=.c++
set GHC_EXT=.hs
set SCALA_EXT=.scala

REM set CPP_OPTIONS=-std=c++11
set CPP_OPTIONS=

IF /I %FILE_EXT% == %CPP_EXT% GOTO __CPPCOMPILE
IF /I %FILE_EXT% == %CC_EXT%  GOTO __CCOMPILE
IF /I %FILE_EXT% == %GHC_EXT% GOTO __HSKCOMPILE
IF /I %FILE_EXT% == %SCALA_EXT% GOTO __SCALACOMPILE
GOTO END

:__CCOMPILE
echo --- Compiling C Program ... ---
call %CC_BIN% %FULL_FILENAME%  -o %FILENAME%.exe & IF ERRORLEVEL 1 (echo. && echo "ERROR - Compilation Error - Please Fix !!!" ) ELSE echo "Compilation success !!!"
GOTO END

:__CPPCOMPILE
echo --- Compiling C++ Program ... ---
call %CPP_BIN% %FULL_FILENAME%  -o %FILENAME%.exe %CPP_OPTIONS% & IF ERRORLEVEL 1 (echo. && echo "ERROR - Compilation Error - Please Fix !!!" ) ELSE echo "Compilation success !!!"
GOTO END

:__HSKCOMPILE
echo --- Compiling Haskell Program ... ---
call %GHC_BIN% --make %FULL_FILENAME%  -o %FILENAME%.exe & IF ERRORLEVEL 1 (echo. && echo "ERROR - Compilation Error - Please Fix !!!" ) ELSE echo "Compilation success !!!"
GOTO END

:__SCALACOMPILE
echo --- Compiling Scala Program ... ---
call %SCALA_BIN% %FULL_FILENAME%  & IF ERRORLEVEL 1 (echo. && echo "ERROR - Compilation Error - Please Fix !!!" ) ELSE echo "Compilation success !!!"
GOTO END

:END

Execute Batch File

@echo off

set FULL_FILENAME=%~1

set FILENAME=%~n1

set DIRNAME=%~dp1

set FILE_EXT=%~x1

echo ++++++++++++++++++++++++++++++++++++++++

echo Executing  %FULL_FILENAME%  ...

echo ++++++++++++++++++++++++++++++++++++++++

set CC_BIN=gcc

set CPP_BIN=g++

set GHC_BIN=ghc

set RUBY_BIN=C:\Ruby21\bin\ruby.exe

set PYTHON_BIN=C:\Python27\python.exe

set SCALA_BIN=scala.bat

set CC_EXT=.c

set CPP_EXT=.c++

set GHC_EXT=.hs

set PY_EXT=.py

set RUBY_EXT=.rb

set SCALA_EXT=.scala

IF /I %FILE_EXT% == %CPP_EXT% GOTO __CPPEXEC

IF /I %FILE_EXT% == %CC_EXT%  GOTO __CEXEC

IF /I %FILE_EXT% == %GHC_EXT% GOTO __HSKEXEC

IF /I %FILE_EXT% == %PY_EXT% GOTO __PYTHONEXEC

IF /I %FILE_EXT% == %RUBY_EXT% GOTO __RUBYEXEC

IF /I %FILE_EXT% == %SCALA_EXT% GOTO __SCALAEXEC

GOTO END

:__CEXEC

call %FILENAME%.exe

GOTO END

:__CPPEXEC

call %FILENAME%.exe

GOTO END

:__HSKEXEC

call %FILENAME%.exe

GOTO END

:__PYTHONEXEC

call %PYTHON_BIN% %FULL_FILENAME%

GOTO END

:__RUBYEXEC

call %RUBY_BIN% %FULL_FILENAME%

GOTO END

:__SCALAEXEC

call %SCALA_BIN% %FILENAME%

GOTO END

:END

echo ++++++++++++++++++++++++++++++++++++++++

echo Execution - Completed !!!

pause