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SED Linux command

SED Linux Command



sed stands for "stream editor".

SYNOPSIS

% sed [-an] command [file ...]
% sed [-an] [-e command] [-f command_file] [file ...]

DESCRIPTION

sed can be used to filter text files. The pattern to match is typically included between a pair of slashes // and quoted.
For EXAMPLE, to print lines containing the string "1024", you may use:

cat filename | sed -n '/1024/p'

Here, sed filters the output from the cat command. The option "-n" tells sed to block all the incoming lines but those explicitly matching the expression. The sed action on a match is "p"= print.
Here is another EXAMPLE, this time for deleting selected lines:

cat filename | sed '/.*o$/d' > new_file

In this EXAMPLE, lines ending with an "o" will be deleted. It uses a regular expression for matching any string followed by an "o" and the end of the line. The output (i.e., all lines but those ending with "o") is directed to new_file.

To search and replace, use the sed 's' action, which comes in front of two expressions:

cat filename | sed 's/string_old/string_new/' > newfile

Linux Books and Interview Questions

Its really important to read right book for your interview and suggesting right books for interview question is the most important thing .

Some books are paid and doesnt contain right questions but some are free and it would be really good if the books are free

Below are some of the free books which is available
free Linux books
Linux Security Books

Technical Interview Questions

Linux Interview Questions

Java Interview Questions

GDB Commands

Qdb commands quick reference . GDB is used to debug C/C++ program on unix.

Below are the quick command of C/C++

Starting GDB

gdb start GDB, with no debugging _les
gdb program begin debugging program
gdb program core debug coredump core produced by program
gdb --help describe command line options

More Help on gdb on starting , stoping setting breakpoint in gdb

How to access Oracle from C++ on Linux ?

It is
Oracle C++ Call Interface
Oracle C++ Call Interface (OCCI) is a high-performance and comprehensive API to access the Oracle database. Based on Standard C++ and object-oriented paradigm, OCCI is designed for improved productivity and quality in developing Oracle database applications.

Introduced in Oracle9i, OCCI is being successfully used for client-server, middle-tier, and complex object modeling applications.

The Instant Client feature makes it extremely easy and fast to deploy an OCCI based application by eliminating the need and disk space of a full Oracle Client install. Users just need to install a small sized archive containing all the Oracle dynamic libraries to run their OCCI applications.

What's new in OCCI in Oracle 11g R1 release :

* Database Resident Connection Pooling(DRCP)
* SecureFile LOBs, Compression, Encryption, and Deduplication
* Client ResultSet cache
* Runtime Connection Load balancing
* Fault Diagnosability
* Objects access performance improvements

Connecting MySQL with C++ on Linux

MySQL API ..
The C API code to connect mysql on unix ( linux ) is being distributed with MySQL. It is the part of mysqlclient library and allows C programs to access a database.

Following packages needs to be compiled to access mysql from C/C++ on unix.

* mysql: MySQL client programs and shared library
* mysqlclient: Backlevel MySQL shared libraries (old libs)
* mysql-devel: Files for development of MySQL applications (a must have)
* mysql-server: Mysql server itself
* gcc, make and other development libs: GNU C compiler


How do I compile and link program against MySQL libs?

$ mysql_config --libs
$ mysql_config --cflags

$ gcc -o output-file $(mysql_config --cflags) mysql-c-api.c $(mysql_config --libs)

$ ./output-file

Sample Program

/* Simple C program that connects to MySQL Database server*/
#include
#include

main() {
MYSQL *conn;
MYSQL_RES *res;
MYSQL_ROW row;

char *server = "localhost";
char *user = "root";
char *password = "PASSWORD"; /* set me first */
char *database = "mysql";

conn = mysql_init(NULL);

/* Connect to database */
if (!mysql_real_connect(conn, server,
user, password, database, 0, NULL, 0)) {
fprintf(stderr, "%s\n", mysql_error(conn));
exit(1);
}

/* send SQL query */
if (mysql_query(conn, "show tables")) {
fprintf(stderr, "%s\n", mysql_error(conn));
exit(1);
}

res = mysql_use_result(conn);

/* output table name */
printf("MySQL Tables in mysql database:\n");
while ((row = mysql_fetch_row(res)) != NULL)
printf("%s \n", row[0]);

/* close connection */
mysql_free_result(res);
mysql_close(conn);
}

Linux Commands Interview Questions

zcat- The zcat utility allows you to examine the contents of a compressed file much the same way that cat displays a file.

top-The top utility shows a listing of all running processes that is dynamically updated.

How do you find out what’s your shell? - echo $SHELL

How do you write a for loop in shell? -

for {variable name} in {list} do {statement} done