#include <stdio.h> #include <stdlib.h> #incl... UNIXguide.net explains this option well: This socket option tells the kernel that even if this port is busy (in the TIME_WAIT state), go ahead and reuse it anyway. If it is busy, but with another state, you will still get an address already in use error. It is useful if your server has been shut down, and then restarted right away while sockets are still active on its port. You should be aware that if any unexpected data comes in, it may confuse your server, but while this is possible, it is not likely. It has been pointed out that "A socket is a 5 tuple (proto, local addr, local port, remote addr, remote port). SO_REUSEADDR just says that you...

String comparison operators: Operator Meaning -n str the length of str is nonzero. -z str the length of str is zero (0). str1 = str2 str1 and str2 are the same (note one equal sign, not two!). str1 != str2 str1 and str2 are not the same. str str is not a null string Examples: # empty string is not null if [ '' ]; then ... Numerical comparisons ( integer expressions only! ): Operator Meaning int1 -eq int2 int1 and int2 are numerically equal int1 -ne int2 int1 and int2 are numerically NOT equal int1 -gt int2 int1 is greater than int2 int1 -ge int2 int1 is greater than or equal to int2 int1 -lt int2 int1 is less than int2 int1 -le...

Got "base64: invalid input" error: $ base64 -d base64_encoded.txt >original.bin ba... which can be easily dismissed as "input is invalid base64 encoded" or "partial input". But I know it's valid base64 encoded input! The problem was, the input was base64 encoded on Windows! The error goes away after converting to Unix format with dos2unix . dos2unix < base64_encoded.txt | base64 -d >origina... Version of base64 used: $ base64 --version base64 (GNU coreutils) 8.5 ...

You get this error when you are trying to compile with JDK 1.5 (class version 49), but your dependency was compiled by JDK 1.6 (class version 50). Check the JAVA_HOME setting, and make sure it's pointing to JDK 1.6. On Unix, use set | grep -i java_home On Windows, just set JAVA_HOME

grep is a versatile command with many variations (grep, egrep, fgrep, then various implementations). It uses a regula expression (regex) pattern to filter input. But then there are basic and extended flavors of regex - leading to even more confusion. And, beware that there are lots of bad examples of regex in the wild... There are two critical questions to ask when you use grep: which grep implementation are you using? what is the flavor of the regex? Here are some examples for gnu grep v2.7: # Find all numbers (no decimal point), basic regex... Use the -o flag to show only the matching part instead of the whole matching line: grep -o -E '\b[0-9]{2}\b' The good thing about the gnu grep is that it...

Problem: cannot connect to PostgreSQL server because of above error. Solution: add the host entries to the /usr/local/pgsql/data/pg_hba.conf file: # TYPE DATABASE USER CIDR-ADDRESS ... Reference for CIDR address: http://oav.net/mirrors/cidr.html

To resolve the error: [focus@bamboo ~]$ psql -U postgres -W Password ... Edit /var/lib/pgsql/data/pg_hba.conf , change ident to trust , then restart postgres: # TYPE DATABASE USER CIDR-ADDRESS ...

Variable Meaning $_ The default or implicit variable. @_ Within a subroutine the array @_ contains the parameters passed to that subroutine. $a, $b Special package variables when using sort() $<digit> Contains the subpattern from the corresponding set of capturing parentheses from the last pattern match, not counting patterns matched in nested blocks that have been exited already. $. Current line number for the last filehandle accessed. $/ The input record separator, newline by default. $| If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is really buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after...

Variables set automatically by shell: Variable Description $# Number of command-line arguments. $- Options currently in effect (arguments supplied to sh or to set). $? Exit value of last executed command. $$ Process number of current process. $! Process number of last background command. $0 First word; that is, command name. $n Individual arguments on command line (positional parameters). The Bourne shell allows only nine parameters to be referenced directly (n = 1-9); the Korn shell allows n to be greater than 9 if specified as ${n}. $* All arguments on command line ("$1 $2..."). $@ All arguments on command line, individually quoted ("$1" "$2" ...). Variables set automatically by Korn shell: Variable Description ERRNO Error number of last system call that failed. LINENO Current...

This is a script to tail a log file through the web browser. It uses AJAX, apache web server, mod_python, UNIX utilities tail (requires the --lines switch) and wc . The log file may reside on the web server or any other host accessible from the web server through SSH. Although it's written in python, it should be easy to port to other languages such as Perl. Apache httpd.conf : LoadModule python_module modules/mod_python.so ... Python script: import time, os from os.path import basename ...