how to replace the 3rd colum? Each line begins similarly, but they all ends variously.
XX YY 03 variable text here
XX YY 03 more variable text here
XX YY 03 even more variable text here really long setence
XX YY 03 variable numbers also appear 03 11. 123 456
XX YY 03 the occasional comma,... (4 Replies)
I have a space delimited text file with 1,000,000+ columns and 100 rows. I want to delete columns 2 through 5 (2 and 5) included from the text file. How do I do that? Thanks. (3 Replies)
I have this space delimited large text file with more than 1,000,000+ columns and about 100 rows. I want to delete all the cells that consist of just 2 (leave 2's that are not by themselves intact):
File before modification
aa bb cc 2 NA100 dd
aa b1 c2 2 NA102 de
File after modification... (1 Reply)
How do you delete cells from a space delimited text file given row and column number? Letś say the row number is r and the column number is c. Thanks! (5 Replies)
I have a space delimited text file with 1,000,000+ columns? I would only like to view specific ones (let's say through 1:10), how can I do that? Thanks! (3 Replies)
I have a text file with irregular spacing between values which makes it really difficult to manipulate. Is there an easy way to convert it into a space delimited text file so that all the spaces, double spaces, triple spaces, tabs between numbers are converted into spaces. The file looks like this:... (5 Replies)
I have a space delimited text file with two columns. I would like to add NA to the first column of the text file.
Input:
19625 10.4791768259
19700 10.8146489183
19701 10.9084026759
19702 10.9861346978
19703 10.9304364984
Output:
NA19625 10.4791768259
NA19700 10.8146489183... (1 Reply)
Hi,
I have a space delimited text file but I only want to change the first space to a tab and keep the rest of the spaces intact. How do I go about doing that? Thanks! (3 Replies)
Discussion started by: evelibertine
3 Replies
LEARN ABOUT FREEBSD
blackhole
BLACKHOLE(4) BSD Kernel Interfaces Manual BLACKHOLE(4)NAME
blackhole -- a sysctl(8) MIB for manipulating behaviour in respect of refused TCP or UDP connection attempts
SYNOPSIS
sysctl net.inet.tcp.blackhole[=[0 | 1 | 2]]
sysctl net.inet.udp.blackhole[=[0 | 1]]
DESCRIPTION
The blackhole sysctl(8) MIB is used to control system behaviour when connection requests are received on TCP or UDP ports where there is no
socket listening.
Normal behaviour, when a TCP SYN segment is received on a port where there is no socket accepting connections, is for the system to return a
RST segment, and drop the connection. The connecting system will see this as a ``Connection refused''. By setting the TCP blackhole MIB to
a numeric value of one, the incoming SYN segment is merely dropped, and no RST is sent, making the system appear as a blackhole. By setting
the MIB value to two, any segment arriving on a closed port is dropped without returning a RST. This provides some degree of protection
against stealth port scans.
In the UDP instance, enabling blackhole behaviour turns off the sending of an ICMP port unreachable message in response to a UDP datagram
which arrives on a port where there is no socket listening. It must be noted that this behaviour will prevent remote systems from running
traceroute(8) to a system.
The blackhole behaviour is useful to slow down anyone who is port scanning a system, attempting to detect vulnerable services on a system.
It could potentially also slow down someone who is attempting a denial of service attack.
WARNING
The TCP and UDP blackhole features should not be regarded as a replacement for firewall solutions. Better security would consist of the
blackhole sysctl(8) MIB used in conjunction with one of the available firewall packages.
This mechanism is not a substitute for securing a system. It should be used together with other security mechanisms.
SEE ALSO ip(4), tcp(4), udp(4), ipf(8), ipfw(8), pfctl(8), sysctl(8)HISTORY
The TCP and UDP blackhole MIBs first appeared in FreeBSD 4.0.
AUTHORS
Geoffrey M. Rehmet
BSD January 1, 2007 BSD