pipe | 易学教程

Why do I need to close fds when reading and writing to the pipe?

阅读更多关于 Why do I need to close fds when reading and writing to the pipe?

问题 Here is an example to illustrate what I mean: #include <stdio.h> #include <unistd.h> #include <sys/types.h> int main(void) { int fd[2], nbytes; pid_t childpid; char string[] = "Hello, world!\n"; char readbuffer[80]; pipe(fd); if((childpid = fork()) == -1) { perror("fork"); exit(1); } if(childpid == 0) { /* Child process closes up input side of pipe */ close(fd[0]); /* Send "string" through the output side of pipe */ write(fd[1], string, (strlen(string)+1)); exit(0); } else { /* Parent process

Program based on pipe in Linux

阅读更多关于 Program based on pipe in Linux

问题 Write a program for this------>>>>>> One program will open a pipe, write a number to pipe. Other program will open the same pipe, will read the number and print them. Close both the pipes. how can i write a program based on this any one knows it then please help me...!!!! 回答1: I think what you're looking for is: echo <number you want to use> (or output from program) | <program you want to pipe into> For instance: echo 5 | more which will simply display: 5 The "|" is your pipe; it redirects

Building a process pipe with ProcessBuilder in Java 7

阅读更多关于 Building a process pipe with ProcessBuilder in Java 7

问题 I've been trying to figure out how to pipe a few processes in Java using the new ProcessBuilder . I can't find a suitable example of what I want to do and when I try to do it myself the process just hangs. I would appreciate a very simple example of some code that runs the equivalent of cat test.txt | wc , but not through a shell. --Update-- OK, just to clarify. I know there are ways to simulate a pipe by reading and writing streams. I'm wondering if that's done in some automatic way by the

assign a value to a variable in a loop

阅读更多关于 assign a value to a variable in a loop

问题 There are 2 pieces of code here, and the value in $1 is the name of a file which contains 3 lines of text. Now, I have a problem. In the first piece of the code, I can't get the "right" value out of the loop, but in the second piece of the code, I can get the right result. I don't know why. How can I make the first piece of the code get the right result? #!/bin/bash count=0 cat "$1" | while read line do count=$[ $count + 1 ] done echo "$count line(s) in all." #--------------------------------

常见Python中调用Linux命令

阅读更多关于常见Python中调用Linux命令

有时候我们需要从Python中执行Linux命令，下面就介绍几种方法？ 1. os 模块：　　1.1 os.system 函数：　　　　system方法会创建子进程运行外部程序，方法只返回外部程序的运行结果。这个方法比较适用于外部程序没有输出结果的情况。 >>> os.system('echo \ "Hello World\"') # 直接使用os.system调用一个echo命令 Hello World 0 >>> os.system("cat /proc/meminfo") MemTotal: 486640 kB MemFree: 301184 kB Buffers: 10304 kB Cached: 58316 kB SwapCached: 0 kB Active: 43748 kB Inactive: 45336 kB Active(anon): 20476 kB Inactive(anon): 520 kB Active(file): 23272 kB Inactive(file): 44816 kB 　　　　注意：上面说了，此方法只会外部程序的结果，也就是os.system的结果，所以如果你想接收命令的返回值，接着向下看　　1.2 os模块的popen方法　　　　当需要得到外部程序的输出结果时，本方法非常有用，返回一个类文件对象，调用该对象的 r ead

How to chain write stream, immediately with a read stream in Node.js 0.10?

阅读更多关于 How to chain write stream, immediately with a read stream in Node.js 0.10?

问题 The following line will download an image file from a specified url variable: var filename = path.join(__dirname, url.replace(/^.*[\\\/]/, '')); request(url).pipe(fs.createWriteStream(filename)); And these lines will take that image and save to MongoDB GridFS: var gfs = Grid(mongoose.connection.db, mongoose.mongo); var writestream = gfs.createWriteStream({ filename: filename }); fs.createReadStream(filename).pipe(writestream); Chaining pipe like this throws Error: 500 Cannot Pipe. Not

How do you specify filenames within a zip when creating it on the command line from a pipe?

阅读更多关于 How do you specify filenames within a zip when creating it on the command line from a pipe?

问题 I'm trying to create a zip file from file contents which are being piped in, e.g. mysql [params and query] | zip -q output.zip - This writes the zip correctly, but when you open the zip, the file within it is called "-". Is there any way of specifying what the filename of the piped in data should be within the zip? 回答1: From what i can gather you cannot do both with the zip command, i mean you cannot both specify the filenames and pipe the content. You can either pipe the contents and the

Python管道进行数据的吞吐处理

阅读更多关于 Python管道进行数据的吞吐处理

import multiprocessing import random import time import datetime import struct import os import getFile # 76(28) + (2048 + 16) * 512 + 4 frame_flag_0 = 0x0000000000000001 # 8 byte frame_flag_1 = 0x0000000000000002 # 8 byte frame_flag_2 = 0x0000000000000003 # 8 byte frame_flag_9 = 0x00000001 # 4 byte dir_name = 'Z:/' file_out = 'Z:/312.dat' def producer(pipe): print('start time: ' + datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')) linestr = getFile.getFileList(dir_name, '_312_') for i in range(0, len(linestr)): file_in = linestr[i] f_in = open(file_in, 'rb') f_in.seek(109) while True:

What's the differences between system and backticks and pipes in Perl?

阅读更多关于 What's the differences between system and backticks and pipes in Perl?

问题 Perl supports three ways (that I know of) of running external programs: system : system PROGRAM LIST as in: system "abc"; backticks as in: `abc`; running it through a pipe as in: open ABC, "abc|"; What are the differences between them? Here's what I know: You can use backticks and pipes to get the output of the command easily. that's it (more in future edits?) 回答1: system(): runs command and returns command's exit status backticks: runs command and returns the command's output pipes : runs

Left side of pipe is the subshell?

阅读更多关于 Left side of pipe is the subshell?

问题 Edit: My comment below regarding sed 's@^@ @' <(f1) is incorrect While $BASH_SUBSHELL indicates that we are in the same level as the launch, the variables are lost in the main script. based on Gordons answer I tested f1 > >(sed 's@^@ @') instead and that seems to work correctly. Still, shouldn't BASH_SUBSHELL should be 1 and not 0 for the first form? Consider this small test #!/bin/bash declare -i i=0 function f1() { let i++ echo "In f1, SUBSHELL: $BASH_SUBSHELL, i=$i" >&2 } f1 f1 | sed 's@^@