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  • What is the difference between "Redirection" and "Pipe"?

    - by John Threepwood
    This question may sound a bit stupid, but I can not really see the difference between redirection and pipes. Redirection is used to redirect the stdout/stdin/stderr, e.g. ls > log.txt. Pipes are used to give the output of a command as input to another command, e.g. ls | grep file.txt. But why are there two operators for the same thing ? Why not just write ls > grep to pass the output through, isn't this just a kind of redirection also ? What I am missing ?

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  • Can't seem to get C TCP Server-Client Communications Right

    - by Zeesponge
    Ok i need some serious help here. I have to make a TCP Server Client. When the Client connects to server using a three stage handshake. AFterwards... while the Client is running in the terminal, the user enters linux shell commands like xinput list, ls -1, ect... something that uses standard output. The server accepts the commands and uses system() (in a fork() in an infinite loop) to run the commands and the standard output is redirected to the client, where the client prints out each line. Afterward the server sends a completion signal of "\377\n". In which the client goes back to the command prompt asking for a new command and closes its connection and exit()'s when inputting "quit". I know that you have to dup2() both the STDOUT_FILENO and STDERR_FILENO to the clients file descriptor {dup2(client_FD, STDOUT_FILENO). Everything works accept when it comes for the client to retrieve system()'s stdout and printing it out... all i get is a blank line with a blinking cursor (client waiting on stdin). I tried all kinds of different routes with no avail... If anyone can help out i would greatly appreciate it TCP SERVER CODE include #include <sys/socket.h> #include <stdio.h> #include <string.h> #include <netinet/in.h> #include <signal.h> #include <unistd.h> #include <stdlib.h> #include <errno.h> //Prototype void handle_client(int connect_fd); int main() { int server_sockfd, client_sockfd; socklen_t server_len, client_len; struct sockaddr_in server_address; struct sockaddr_in client_address; server_sockfd = socket(AF_INET, SOCK_STREAM, 0); server_address.sin_family = AF_INET; server_address.sin_addr.s_addr = htonl(INADDR_ANY); server_address.sin_port = htons(9734); server_len = sizeof(server_address); bind(server_sockfd, (struct sockaddr *)&server_address, server_len); /* Create a connection queue, ignore child exit details and wait for clients. */ listen(server_sockfd, 10); signal(SIGCHLD, SIG_IGN); while(1) { printf("server waiting\n"); client_len = sizeof(client_address); client_sockfd = accept(server_sockfd, (struct sockaddr *)&client_address, &client_len); if(fork() == 0) handle_client(client_sockfd); else close(client_sockfd); } } void handle_client(int connect_fd) { const char* remsh = "<remsh>\n"; const char* ready = "<ready>\n"; const char* ok = "<ok>\n"; const char* command = "<command>\n"; const char* complete = "<\377\n"; const char* shared_secret = "<shapoopi>\n"; static char server_msg[201]; static char client_msg[201]; static char commands[201]; int sys_return; //memset client_msg, server_msg, commands memset(&client_msg, 0, sizeof(client_msg)); memset(&server_msg, 0, sizeof(client_msg)); memset(&commands, 0, sizeof(commands)); //read remsh from client read(connect_fd, &client_msg, 200); //check remsh validity from client if(strcmp(client_msg, remsh) != 0) { errno++; perror("Error Establishing Handshake"); close(connect_fd); exit(1); } //memset client_msg memset(&client_msg, 0, sizeof(client_msg)); //write remsh to client write(connect_fd, remsh, strlen(remsh)); //read shared_secret from client read(connect_fd, &client_msg, 200); //check shared_secret validity from client if(strcmp(client_msg, shared_secret) != 0) { errno++; perror("Invalid Security Passphrase"); write(connect_fd, "no", 2); close(connect_fd); exit(1); } //memset client_msg memset(&client_msg, 0, sizeof(client_msg)); //write ok to client write(connect_fd, ok, strlen(ok)); // dup2 STDOUT_FILENO <= client fd, STDERR_FILENO <= client fd dup2(connect_fd, STDOUT_FILENO); dup2(connect_fd, STDERR_FILENO); //begin while... while read (client_msg) from server and >0 while(read(connect_fd, &client_msg, 200) > 0) { //check command validity from client if(strcmp(client_msg, command) != 0) { errno++; perror("Error, unable to retrieve data"); close(connect_fd); exit(1); } //memset client_msg memset(&client_msg, 0, sizeof(client_msg)); //write ready to client write(connect_fd, ready, strlen(ready)); //read commands from client read(connect_fd, &commands, 200); //run commands using system( ) sys_return = system(commands); //check success of system( ) if(sys_return < 0) { perror("Invalid Commands"); errno++; } //memset commands memset(commands, 0, sizeof(commands)); //write complete to client write(connect_fd, complete, sizeof(complete)); } } TCP CLIENT CODE #include <sys/types.h> #include <sys/socket.h> #include <stdio.h> #include <string.h> #include <netinet/in.h> #include <arpa/inet.h> #include <unistd.h> #include <stdlib.h> #include <errno.h> #include "readline.c" int main(int argc, char *argv[]) { int sockfd; int len; struct sockaddr_in address; int result; const char* remsh = "<remsh>\n"; const char* ready = "<ready>\n"; const char* ok = "<ok>\n"; const char* command = "<command>\n"; const char* complete = "<\377\n"; const char* shared_secret = "<shapoopi>\n"; static char server_msg[201]; static char client_msg[201]; memset(&client_msg, 0, sizeof(client_msg)); memset(&server_msg, 0, sizeof(server_msg)); /* Create a socket for the client. */ sockfd = socket(AF_INET, SOCK_STREAM, 0); /* Name the socket, as agreed with the server. */ memset(&address, 0, sizeof(address)); address.sin_family = AF_INET; address.sin_addr.s_addr = inet_addr(argv[1]); address.sin_port = htons(9734); len = sizeof(address); /* Now connect our socket to the server's socket. */ result = connect(sockfd, (struct sockaddr *)&address, len); if(result == -1) { perror("ACCESS DENIED"); exit(1); } //write remsh to server write(sockfd, remsh, strlen(remsh)); //read remsh from server read(sockfd, &server_msg, 200); //check remsh validity from server if(strcmp(server_msg, remsh) != 0) { errno++; perror("Error Establishing Initial Handshake"); close(sockfd); exit(1); } //memset server_msg memset(&server_msg, 0, sizeof(server_msg)); //write shared secret text to server write(sockfd, shared_secret, strlen(shared_secret)); //read ok from server read(sockfd, &server_msg, 200); //check ok velidity from server if(strcmp(server_msg, ok) != 0 ) { errno++; perror("Incorrect security phrase"); close(sockfd); exit(1); } //? dup2 STDIN_FILENO = server socket fd? //dup2(sockfd, STDIN_FILENO); //begin while(1)/////////////////////////////////////// while(1){ //memset both msg arrays memset(&client_msg, 0, sizeof(client_msg)); memset(&server_msg, 0, sizeof(server_msg)); //print Enter Command, scan input, fflush to stdout printf("<<Enter Command>> "); scanf("%s", client_msg); fflush(stdout); //check quit input, if true close and exit successfully if(strcmp(client_msg, "quit") == 0) { printf("Exiting\n"); close(sockfd); exit(EXIT_SUCCESS); } //write command to server write(sockfd, command, strlen(command)); //read ready from server read(sockfd, &server_msg, 200); //check ready validity from server if(strcmp(server_msg, ready) != 0) { errno++; perror("Failed Server Communications"); close(sockfd); exit(1); } //memset server_msg memset(&server_msg, 0, sizeof(server_msg)); //begin looping and retrieving from stdin, //break loop at EOF or complete while((read(sockfd, server_msg, 200) != 0) && (strcmp(server_msg, complete) != 0)) { //while((fgets(server_msg, 4096, stdin) != EOF) || (strcmp(server_msg, complete) == 0)) { printf("%s", server_msg); memset(&server_msg, 0, sizeof(server_msg)); } } }

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  • Installing Pycurl on CentOS?

    - by RadiantHex
    Hi folks, I'm finding it to install pycurl on CentOS 5 quite the mission impossible. This is the error I'm getting: >>> import pycurl Traceback (most recent call last): File "<stdin>", line 1, in <module> ImportError: libcurl.so.4: cannot open shared object file: No such file or directory Some help would be beyond amazing. :|

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  • Python - Execute Process -> Block till it exits & Supress Output

    - by Jason
    Hi, I'm using the following to execute a process and hide its output from Python. It's in a loop though, and I need a way to block until the sub process has terminated before moving to the next iteration. subprocess.Popen(["scanx", "--udp", host], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE) Thanks for any help.

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  • how to read input with multiple lines in java

    - by Gandalf StormCrow
    Hi all, Our professor is making us do some basic programming with java, he gaves a website and everything to register and submit our questions, for today I need to do this one example I feel like I'm on the right track but I just can't figure out the rest .. here is the actualy question : **Sample Input:** 10 12 10 14 100 200 **Sample Output:** 2 4 100 And here is what I've got so far : public class Practice { public static int calculateAnswer(String a, String b) { return (Integer.parseInt(b) - Integer.parseInt(a)); } public static void main(String[] args) { System.out.println(calculateAnswer(args[0], args[1])); } } Now I always get the answer 2 because I'm reading the single line, how can I take all lines into account? thank you For some strange reason everytime I want to execute I get this error: C:\sonic>java Practice.class 10 12 Exception in thread "main" java.lang.NoClassDefFoundError: Fact Caused by: java.lang.ClassNotFoundException: Fact.class at java.net.URLClassLoader$1.run(URLClassLoader.java:20 at java.security.AccessController.doPrivileged(Native M at java.net.URLClassLoader.findClass(URLClassLoader.jav at java.lang.ClassLoader.loadClass(ClassLoader.java:307 at sun.misc.Launcher$AppClassLoader.loadClass(Launcher. at java.lang.ClassLoader.loadClass(ClassLoader.java:248 Could not find the main class: Practice.class. Program will exit. Whosever version of answer I use I get this error, what do I do ? However if I run it in eclipse Run as Run Configuration - Program arguments 10 12 10 14 100 200 I get no output EDIT I have made some progress, at first I was getting the compilation error, then runtime error and now I get wrong answer , so can anybody help me what is wrong with this : import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.math.BigInteger; public class Practice { public static BigInteger calculateAnswer(String a, String b) { BigInteger ab = new BigInteger(a); BigInteger bc = new BigInteger(b); return bc.subtract(ab); } public static void main(String[] args) throws IOException { BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); String line; while ((line = stdin.readLine()) != null && line.length()!= 0) { String[] input = line.split(" "); if (input.length == 2) { System.out.println(calculateAnswer(input[0], input[1])); } } } }

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  • Input event loop in a console application

    - by Álvaro
    Hi, I'm trying to make a little console application that is able to deal with keystrokes as events. What I need is mostly the ability to get the keystrokes and be able to do something with them without dealing with the typical stdin reading functions. I tried to check the code of programs like mplayer, which implement this (for stopping the play, for example), but I can't get to the core of this with such a big code base. Thanks

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  • Asynchronous subprocess on Windows

    - by Stigma
    First of all, the overall problem I am solving is a bit more complicated than I am showing here, so please do not tell me 'use threads with blocking' as it would not solve my actual situation without a fair, FAIR bit of rewriting and refactoring. I have several applications which are not mine to modify, which take data from stdin and poop it out on stdout after doing their magic. My task is to chain several of these programs. Problem is, sometimes they choke, and as such I need to track their progress which is outputted on STDERR. pA = subprocess.Popen(CommandA, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE) # ... some more processes make up the chain, but that is irrelevant to the problem pB = subprocess.Popen(CommandB, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=pA.stdout ) Now, reading directly through pA.stdout.readline() and pB.stdout.readline(), or the plain read() functions, is a blocking matter. Since different applications output in different paces and different formats, blocking is not an option. (And as I wrote above, threading is not an option unless at a last, last resort.) pA.communicate() is deadlock safe, but since I need the information live, that is not an option either. Thus google brought me to this asynchronous subprocess snippet on ActiveState. All good at first, until I implement it. Comparing the cmd.exe output of pA.exe | pB.exe, ignoring the fact both output to the same window making for a mess, I see very instantaneous updates. However, I implement the same thing using the above snippet and the read_some() function declared there, and it takes over 10 seconds to notify updates of a single pipe. But when it does, it has updates leading all the way upto 40% progress, for example. Thus I do some more research, and see numerous subjects concerning PeekNamedPipe, anonymous handles, and returning 0 bytes available even though there is information available in the pipe. As the subject has proven quite a bit beyond my expertise to fix or code around, I come to Stack Overflow to look for guidance. :) My platform is W7 64-bit with Python 2.6, the applications are 32-bit in case it matters, and compatibility with Unix is not a concern. I can even deal with a full ctypes or pywin32 solution that subverts subprocess entirely if it is the only solution, as long as I can read from every stderr pipe asynchronously with immediate performance and no deadlocks. :)

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  • Signal Handling in C

    - by Dave
    How can I implement signal Handling for Ctrl-C and Ctrl-D in C....So If Ctrl-C is pressed then the program will ignore and try to get the input from the user again...If Ctrl-D is pressed then the program will terminate... My program follows: int main(){ char msg[400]; while(1){ printf("Enter: "); fgets(msg,400,stdin); printf("%s\n",msg); } } Thanks, Dave

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  • Perl regex matching output from `w -hs` command

    - by Bushman
    I'm trying to write a Perl script that will work better with KDE's kwrited, which, as far as I can tell, is connected to a pts and puts every line it receives through the KDE system tray notifications, with the title "KDE write daemon". Unfortunately, it makes a separate notification for each and every line, so it spams up the system tray with multiline messages on regular old write, and for some reason it cuts off the entire last line of the message when using wall (One-line messages are also goners.). I was also hoping to make it so that it could broadcast across a LAN with thick clients. Before starting on that (which would require ssh, of course), I tried to make an ssh-less version to make sure it works. Unfortunately, it doesn't. perl ./write.pl "Testing 1 2 3" where the following is the contents of ./write.pl: #!/usr/bin/perl use strict; use warnings; my $message = ""; my $device = ""; my $possibledevice = '`w -hs | grep "/usr/bin/kwrited"`'; #Where is kwrited? $possibledevice =~ s/^[^\t][\t]//; $possibledevice =~ s/[\t][^\t][\t ]\/usr\/bin\/kwrited$//; $possibledevice = '/dev/'.$possibledevice; unless ($possibledevice eq "") { $device = $possibledevice; } if ($ARGV[0] ne "") { $message = $ARGV[0]; $device = $ARGV[1]; } else { $device = $ARGV[0] unless $ARGV[0] eq ""; while (<STDIN>) { chomp; $message .= <STDIN>; } } if ($message ne "") { system "echo \'$message\' > $device"; } else { print "Error: empty message" } produces the following error: $ perl write.pl "Testing 1 2 3" Use of uninitialized value $device in concatenation (.) or string at write.pl line 29. sh: -c: line 0: syntax error near unexpected token `newline' sh: -c: line 0: `echo 'foo' > ' Somehow, the regular expressions and/or the backtick escape in processing $possibledevice are not working properly, because where kwrited is connected to /dev/pts/0, the following works perfectly: $ perl write.pl "Testing 1 2 3" /dev/pts/0

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  • Python 3.1.1 string to hex

    - by Stuart
    I am trying to use str.encode() but I get >>> "hello".encode(hex) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: must be string, not builtin_function_or_method I have tried a bunch of variations and they seem to all work in Python 2.5.2, so what do I need to do to get them to work in Python 3.1?

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  • ignore extra spaces when using fgets

    - by Gary
    Hi, I'm using fgets with stdin to read in some data, with the max length i read in being 25. With one of the tests I'm running on this code, there are a few hundred spaces after the data that I want - which causes the program to fail. Can someone advise me as to how to ignore all of these extra spaces when using fgets and go to the next line? Thanks

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  • Pylucene in Python 2.6 + MacOs Snow Leopard

    - by jbastos
    Greetings, I'm trying to install Pylucene on my 32-bit python running on Snow Leopard. I compiled JCC with success. But I get warnings while making pylucene: ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/__init__.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/__wrap01__.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/__wrap02__.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/__wrap03__.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/functions.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/JArray.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/JObject.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/lucene.o, file is not of required architecture ld: warning: in build/temp.macosx-10.6-i386-2.6/build/_lucene/types.o, file is not of required architecture ld: warning: in /Developer/SDKs/MacOSX10.4u.sdk/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/JCC-2.3-py2.6-macosx-10.3-fat.egg/libjcc.dylib, file is not of required architecture ld: warning: in /Developer/SDKs/MacOSX10.4u.sdk/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/JCC-2.3-py2.6-macosx-10.3-fat.egg/libjcc.dylib, file is not of required architecture build of complete Then I try to import lucene: MacBookPro:~/tmp/trunk python Python 2.6.3 (r263:75184, Oct 2 2009, 07:56:03) [GCC 4.0.1 (Apple Inc. build 5493)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import pylucene Traceback (most recent call last): File "<stdin>", line 1, in <module> ImportError: No module named pylucene >>> import lucene Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/lucene-2.9.0-py2.6-macosx-10.6-i386.egg/lucene/__init__.py", line 7, in <module> import _lucene ImportError: dlopen(/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/lucene-2.9.0-py2.6-macosx-10.6-i386.egg/lucene/_lucene.so, 2): Symbol not found: __Z8getVMEnvP7_object Referenced from: /Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/lucene-2.9.0-py2.6-macosx-10.6-i386.egg/lucene/_lucene.so Expected in: flat namespace in /Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/lucene-2.9.0-py2.6-macosx-10.6-i386.egg/lucene/_lucene.so >>> Any hints?

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  • Quality gets worse

    - by Hopery
    I have bunch of flash videos and am adding my brand to all of them. The problem is quality gets worse. I am doing with this command: ffmpeg -i /input.flv -vhook "/usr/loca/vhook/drawtext.so -f /usr/share/fonts/somefont.ttf -x 5 -y 5 t MyBrand" -f flv -s 320x240 - | flvtools2 -U stdin /output.flv Please tell me what I am doing wrong. I need the same quality.

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  • insert multiple elements in string in python

    - by Anurag Sharma
    I have to build a string like this { name: "john", url: "www.dkd.com", email: "[email protected]" } where john, www.dkd.com and [email protected] are to be supplied by variables I tried to do the following s1 = "{'name:' {0},'url:' {1},'emailid:' {2}}" s1.format("john","www.dkd.com","[email protected]") I am getting the following error Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: "'name" Dont able to understand what I am doing wrong

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  • Stream writing lags my GUI

    - by blez
    I have a thread that dequeues data from a queue and write it to another application's STDIN. I'm using Stream, but with .Write and even .BeginWrite, when I send 1mb chunks to the second app, my GUI gets laggy for ~1sec. Why?

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  • java program support multiple languages

    - by Alaa
    hello every one , how can i make java program working with multiple languages (frensh, english , arabic .. etc) , i mean i wanna make a comboBox ,when i choose one language, all the labels in the GUI interfaces change to the selected language and even the stdin also change to that language. thanx in advance Alaa

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  • pipe multiple files (gz) into c program,

    - by monkeyking
    Ive written a cprogram that works when i pipe data into my program using stdin like gunzip -c IN.gz|./a.out If I want to run my program on a list of files I can do something like for i `cat list.txt` do gunzip -c $i |./a.out done But this will start my program 'number of files' times. I'm interested in piping all the files into the same process run. Like doing for i `cat list.txt` do gunzip -c $i >>tmp done cat tmp |./a.out thanks.

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  • Iterating over key and value of defaultdict dictionaries

    - by gf
    The following works as expected: d = [(1,2), (3,4)] for k,v in d: print "%s - %s" % (str(k), str(v)) But this fails: d = collections.defaultdict(int) d[1] = 2 d[3] = 4 for k,v in d: print "%s - %s" % (str(k), str(v)) With: Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'int' object is not iterable Why? How can i fix it?

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  • Why does Python Array Module Process Strings and Lists Differently?

    - by Casey
    I'm having trouble understanding the result of the following statements: >>> from array import array >>> array('L',[0xff,0xff,0xff,0xff]) array('L', [255L, 255L, 255L, 255L]) >>> from array import array >>> array('L','\xff\xff\xff\xff') Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: string length not a multiple of item size

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