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Top Forums Shell Programming and Scripting Don't understand how RS functions in awk Post 302449029 by joe228 on Friday 27th of August 2010 11:31:47 PM
Old 08-28-2010
Don't understand how RS functions in awk

I learn using RS in awk to extract portion of file in this forum which is wonderful solution to the problem. However, I don't understand how exactly it operates.

I don't quite understand the mechanism behind how searching for /DATA2/ can result in extracting the whole section under "DATA2"

sample
=====
Code:
DATA1
data11
data12

DATA2
data21
data22

DATA3
data31
data32

Code:
$cat sample | awk 'BEGIN {RS=""} /DATA2/'
DATA2
data21
data22

Since RS is set to be empty string, so each line now should be regarded as a field and so I expected printing $1 and $2 would give me the output of DATA1 and data11 but it didn't. Instead, it returned me with what is shown below:

Code:
$ cat sample | awk 'BEGIN {RS=""} { print $1 }'
DATA1
DATA2
DATA3
$ cat sample | awk 'BEGIN {RS=""} { print $2 }'
data11
data21
data31

So, can someone explain to me why it behaved this way?? Thanks!


Moderator's Comments:
Mod Comment Please use code tags, thank you!

Last edited by Franklin52; 08-28-2010 at 09:14 AM..
 

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SSL_CTX_new(3SSL)						      OpenSSL							 SSL_CTX_new(3SSL)

NAME
SSL_CTX_new - create a new SSL_CTX object as framework for TLS/SSL enabled functions SYNOPSIS
#include <openssl/ssl.h> SSL_CTX *SSL_CTX_new(const SSL_METHOD *method); DESCRIPTION
SSL_CTX_new() creates a new SSL_CTX object as framework to establish TLS/SSL enabled connections. NOTES
The SSL_CTX object uses method as connection method. The methods exist in a generic type (for client and server use), a server only type, and a client only type. method can be of the following types: SSLv2_method(void), SSLv2_server_method(void), SSLv2_client_method(void) A TLS/SSL connection established with these methods will only understand the SSLv2 protocol. A client will send out SSLv2 client hello messages and will also indicate that it only understand SSLv2. A server will only understand SSLv2 client hello messages. SSLv3_method(void), SSLv3_server_method(void), SSLv3_client_method(void) A TLS/SSL connection established with these methods will only understand the SSLv3 protocol. A client will send out SSLv3 client hello messages and will indicate that it only understands SSLv3. A server will only understand SSLv3 client hello messages. This especially means, that it will not understand SSLv2 client hello messages which are widely used for compatibility reasons, see SSLv23_*_method(). TLSv1_method(void), TLSv1_server_method(void), TLSv1_client_method(void) A TLS/SSL connection established with these methods will only understand the TLSv1 protocol. A client will send out TLSv1 client hello messages and will indicate that it only understands TLSv1. A server will only understand TLSv1 client hello messages. This especially means, that it will not understand SSLv2 client hello messages which are widely used for compatibility reasons, see SSLv23_*_method(). It will also not understand SSLv3 client hello messages. SSLv23_method(void), SSLv23_server_method(void), SSLv23_client_method(void) A TLS/SSL connection established with these methods will understand the SSLv2, SSLv3, and TLSv1 protocol. A client will send out SSLv2 client hello messages and will indicate that it also understands SSLv3 and TLSv1. A server will understand SSLv2, SSLv3, and TLSv1 client hello messages. This is the best choice when compatibility is a concern. The list of protocols available can later be limited using the SSL_OP_NO_SSLv2, SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1 options of the SSL_CTX_set_options() or SSL_set_options() functions. Using these options it is possible to choose e.g. SSLv23_server_method() and be able to negotiate with all possible clients, but to only allow newer protocols like SSLv3 or TLSv1. SSL_CTX_new() initializes the list of ciphers, the session cache setting, the callbacks, the keys and certificates, and the options to its default values. RETURN VALUES
The following return values can occur: NULL The creation of a new SSL_CTX object failed. Check the error stack to find out the reason. Pointer to an SSL_CTX object The return value points to an allocated SSL_CTX object. SEE ALSO
SSL_CTX_free(3), SSL_accept(3), ssl(3), SSL_set_connect_state(3) 1.0.1e 2013-02-11 SSL_CTX_new(3SSL)
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