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HowTo: Revoke OpenSSH Keys and Disable User Access

Many users are using ssh to log into a remote machine and append the indicated identity file to machine’s ~/.ssh/authorized_keys file. I recently moved one of my server, and I would like to revoke openssh keys and disable user access under Linux operating systems. How do I revoke OpenSSH keys under Unix or Linux operating systems?
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Linux / Unix: sed Command Print Only Matching Lines

I see many examples and man pages on how to do operations like search-and-replace using sed. But, I want to match a given string or a regular pattern expression and display on the screen. How do I print lines with matching pattern using sed command only under Unix like operating systems?
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Unix / Linux: Maximum Character Length of Arguments In a Shell Command

What is the maximum character length of arguments in a shell command? How do I find out the maximum length of arguments for a new process under Linux or Unix like operating systems?
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Linux / Unix: Find Out DNS Server IP Address / Names

How do I find out my DNS server IP address assiged my my ISP under Unix or Linux operating system using command prompt? How do I find preferred dns server under Debian / Ubuntu / Fedora Linux desktop system?
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awk: warning: escape sequence '\<' treated as plain '>'

I‘m trying to match words using GNU awk command and getting the following error:

echo 'foo bar this that blah' | awk '{gsub("\<regex-word\>", "NEW-WORD");print}'

But getting the following warning on screen and it is not working:
awk: warning: escape sequence `\< ' treated as plain `<' awk: warning: escape sequence `\>' treated as plain `>'

How do I fix this problem under Unix like operating systems?
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Linux / Unix rsync: Delete Source File After Transfer

I would like to move all desktop:~/Downloads/*.avi files from my desktop to laptop:~/Download/ using rsync. How do I delete source file after successful transfer is done using rsync command under BSD/Unix/Linux/Apple OS X operating systems?
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Bash History: Correct / Repeat The Last Command With a Substitution

I often type the wrong command as follows under Linux bash shell:

rsync -av dir1 user@server1.cyberciti.biz:/path/to/dir1


cp -av file1*.txt file2*.txt /path/to/dest

I need to correct those command as follows:

rsync -av dir5 user@server1.cyberciti.biz:/path/to/dir1
cp -av delta1*.txt delta2*.txt /path/to/dest

How do I replace dir1 with dir5 or file with delta and repeat the last command under bash shell?
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HowTo: grep Text Between Two Words in Unix / Linux

I got over 100s of HTML files in the following format:

 <TITLE>Statistics for ABC LTD - January 2007 - Rang IDXYZZAZZZZ</TITLE>
<BODY BGCOLOR="#E8E8E8" TEXT="#000000" LINK="#0000FF" VLINK="#FF0000">
<H2>Statistics for ABC LTF</H2>
Summary Period: January 2007<BR>
Generated 01-Feb-2007 06:40 CET<BR>
my data 1
my data 2
my data 3
my data 10000
my data N times

Generated by MyAppDbStatsWriter (UNIX) version 1.9b2

How do I extract text between two words (<PRE> and </PRE>) in unix or linux using grep command?
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Linux / Unix: lftp Command Mirror Files and Directories

How do I mirror files from remote ftp server using lftp command? How do put the entier directory from a local disk to a remote ftp server (reverse mirror) using lftp command under Linux and Unix like operating systems?
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Add / Import .SQL file To MySQL Database Server

How do I import a MySQL .SQL text file to MySQL database sever using command line or gui tools?
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