Pipes or named pipes are a feature of the POSIX standard that allow separate processes to communicate with each other without having been designed explicitly to work together.

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How does piping/redirection in Linux work exactly?

I have these three examples of redirection stdin/stdout, only one of them is working the way it is intended to. I would love if someone can explain that to me. The goal is to sort the contents in ...
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2answers
3k views

BASH - Check if unnamed pipe is empty

My problem is, I want a script which reads content from a pipe, checks if it's empty and output it if not, as seen here: #!/bin/bash var=$(cat -) if [ -n "$var" ] then echo "$var" else echo ...
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1answer
20 views

Using -replace on pipes in powershell

I want to test out a replace before I use it, so I'm trying to write a quick online command to see what the output is. However, I'm not sure what the syntax is. What I want to do is something like ...
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1answer
130 views

Continuous streaming from an empty pipe, then adding data to the pipe on demand

Essentially, what I'd like to do is to have ffmpeg continuously stream to an RTMP server using an empty pipe, then when I want to stream something, add data to the pipe. My reasons for doing this ...
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0answers
19 views

Pipeline from <filename> to <filename> in Windows CMD?

Is there a way to do this without a temporary file? I've tried with tee but that failed. Test case: >echo "foo bar" > ex2.go >type ex2.go "foo bar" >type ex2.go > ex2.go >type ...
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3answers
310 views

Need to understand the concept of xargs and pipes

I have been struggling with this issue for a while now and would really appreciate it if someone could clarify it for me . Suppose I am trying to pipe the two commands together. readlink and cat ...
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1answer
48 views

Piping lines to repeat commands

If my grep operation returns a list of IDs like in the following, can I somehow feed/pipe each line to a commandline command's parameter?: 12345 84758 49549 .. Like for example with the above ...
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0answers
27 views

How to pipe arguments into stdin?

I am trying to generate a private key using keytool command, but it asks me for many details like my key passphrase, my name and my organization details. I want to pass all the inputs in one command. ...
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1answer
44 views

Piping grep causes error $'\302\240grep': command not found on linux

Sometimes when I'm catting & grepping a file, I see this error come up: $ cat something.txt | grep "some text" -bash: $'\302\240grep': command not found When I re-type the command, it works as ...
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2answers
934 views

How to find the last match of a string in a bunch of files

I have a bunch of files, I'd like to find the last match of a string in each of them. grep text *.file gives me all the matches not the last ones. ls *.file | xargs grep text | tail -n 1 gives me ...
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18 views

How can I format the piped and refreshing output of multiple cmmands nicely?

I have a command line of multiple piped commands which executes beautifully in bash. For simplification: command1 | command2 | command3 Each command generates output while running, resetting the ...
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1answer
19 views

Detect IPC between running processes on Unix

Suppose I have 2 processes on any unix-based system and I sure they are using some inter-process communication. How can I detect what do they use in order to simulate or hook it? I mean pipes, for ...
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1answer
50 views

Batch to retrieve TFS version erroring in FOR /F where TFS attempts to PIPE to findstr

I have this partial batch, but it gives me an error (On 64 bit installations) SETLOCAL EnableDelayedExpansion REM Figure out what ProgramFiles Root we run the command SET ...
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3answers
271 views

Execute command in-between a bash pipe row …?

I want to run a series of piped commands which do a lot of audioprocessing. It looks as follows in pseudocode: command1 | command2 | command3 Of command2 and command3, both take the output of the ...
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3answers
93 views

real windows equivalent to cat *stdin*

Under cmd is there a windows equivalent to the posix command cat ? cat all by itself no filenames, no switches. I just want something that copies stdin to stdout until it hits EOF. it's not a hard ...
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1answer
48 views

How can I use the pipeline output from different commands inside a custom bash script?

I have this simple script: #!/bin/bash # This command removes the last "\n" (line feed) character from the file specified as parameter # # Params: # $1 [FILE_NAME] - the name of the file to trim if ...
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2answers
85 views

How to save console output still showing it

I need to troubleshoot a telnet session and send save it's results to another person. When I use redirection I save the contents of my session, but I'm not able to see it on console. How to pipe ...
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1answer
1k views

Rendering HTML from a pipe

I would like to be able to generate HTML then pipe it to a program which will render it, something like this: for i in 1 2 3 do for j in a b c do echo "<table ...
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5answers
7k views

How can I save the current contents of less to a file?

If I've piped the results of a command to less and then decided that I want to save the contents to a file, is this possible? I've tried setting a mark a at the end of the buffer, and then returning ...
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1answer
19 views

pv: Change Prefix on the Fly

To me pv is really handy some times. However, I was wondering if it was possible to change the prefix on the fly. I mean usually I have something like in.sh | pv -btrcN "Watch that work!!1!" | ...
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1answer
54 views

Passing the output of locate as an argument to an editor

What I mean is doing this in a 1-liner: ubu@ubuntu:~$ locate filename.sh /home/ubu/path/to/filename.sh ubu@ubuntu:~$ gedit /home/ubu/path/to/filename.sh I can't seem to figure out the right piping ...
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1answer
53 views

redirect a file generated by a program to another program

In linux enviroment, I have a program that creates a large file (2-3GB). I need to filter this file (e.g. I want to remove a line if it appears in the precedeing 10 lines). I want to do it while the ...
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1answer
94 views

How to split and recombine stdout pipe in bash?

I am parsing text on the command line. How can I take the output of one command and use it in two places in the next command? some_command | head -n $( awk '/search_term/ {print FNR} ...
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1answer
17 views

Is it possible to count from a given number when extracting images from a video with FFmpeg?

I am using ffmpeg to extract still images from a video. First from the beginning of the video, to a given time and then from the end of the video from a given time. So I am using two ffmpeg command ...
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1answer
41 views

Pipe standard error to file and keep it on standard error?

I have a script (fragment) for which I'm logging output and standard error: #!/bin/sh #... { date "+%Y-%m-%d %T" cd $workdir ls -ltr validfile badfile #example command that provides stdout, ...
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152 views

Pipe ffmpeg->ffmbc cut files after some length

I recently tried the following command: ffmpeg.exe -i "C:\Users\Dennis\git\cnn\CNN\watch\filea.mp4" -i "C:\Users\Dennis\git\cnn\CNN\watch\fileb.mp4" -filter_complex ...
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2answers
477 views

How to unrar the STDIN?

What I have tried: cat archive.rar | unrar x - cat archive.rar | unrar x /dev/stdin cat archive.rar | 7z x - cat archive.rar | 7z x -si cat archive.rar | 7z l -si The unrar doesn't recognise the - ...
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43 views

Win7 Command Line piping

I want to know why in the command line prompt this happens. I have a script fileX.cmd which is one single line of text: @echo dir If I do C:\Users\Dogfood>fileX.cmd | cmd This will show all ...
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2answers
55 views

Ping piped to txt does output nothing

Following script should pipe the ping output to a text file @echo off rem end with ctrl+c y ping 192.168.33.65 -t >> C:\_ScriptLog\Ping\ping.txt but nothing is piped to the txt file, it´s ...
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5k views

How to rate-limit a pipe under linux?

Is there a filter which I could use to rate-limit a pipe on linux? If this exists, let call it rate-limit, I want to be able to type in a terminal something like cat /dev/urandom | rate-limit 3 -k | ...
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How do I output a variable without changing if it has a newline or not in a shell script?

I have a shell script that takes input from another shell script. The stream gets piped in on stdin. I need to capture all the bytes of the stdin stream to a single variable in the shell script. ...
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3k views

How to redirect the output of a program to the Linux diff command

I have a program that writes to stdout. Is there a way that I can redirect the output to the Linux diff command or do I have to write the output to a file and then compare that? For example, I have a ...
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4answers
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cURL: how to suppress strange output when redirecting?

I'm trying to print just the verbose sections of a cURL request (which are sent to stderr) from the bash shell. But when I redirect stdout like this: curl -v http://somehost/somepage > /dev/null ...
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0answers
17 views

Merge two outputs into one in real time without scrambling them in linux

Is it possible to merge two real time outputs into one file without scrambling the new lines? What I want to do is something like cat <(/proc/kmsg) <(while true; do echo hello; sleep 1; done) ...
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1answer
117 views

How to parse pipe with multiple commands independently?

How can I parse output of a single command by multiple commands without truncating at each step? For example ls -al|grep -i something will pass every line that has "something" in it to the next ...
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2answers
40 views

Trying to cat the result of piped commands

I have a folder of files that are named list20140801.txt list20140802.txt .... I'm trying to do this ls | sort | tail -3 | cat But it is just giving me the file names, not cat'ing them.
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5answers
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How to get both PIPESTATUS and output in bash script

I'm trying to get last modification date of a file with this command TM_LOCAL=`ls -l --time-style=long-iso ~/.vimrc | awk '{ print $6" "$7 }'` TM_LOCAL has value like "2012-05-16 23:18" after ...
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1answer
339 views

Multiple unix pipes not working

This first pipeline works fine (printing "c"): echo "a" | sed 's/a/b/' | sed 's/b/c/' This one does not do what I expect (nothing gets printed when I feed an "a" into my fifo ): mkfifo fifo; cat ...
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6answers
1k views

How can I both pipe and display output in Windows' command line?

I have a process I need to run within a batch file. This process produces some output. I need to both display this output to the screen and send (pipe) it to another program. The bash method uses ...
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3answers
93 views

Pass stdin to multiple programs without closing

I want to split and GZip a large file, and this answer appeared to be what I'm looking for, and it seemed like a very useful way of doing things I never thought of, so I'd like to generalize it; the ...
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1answer
207 views

How to shuffle large text files efficiently while piping it on Linux?

I have a text file that is couple GBs. I am trying to shuffle this text file in a pipe. For example these are some sample lines of what I am using but it is not efficient and in fact the pipe does ...
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3answers
6k views

Silence curl with >/dev/null 2>&1 when it's piped

So I have a curl that is piped to a grep and a sed. Where would I apply the >/dev/null 2>&1 ? curl www.site.com | grep stuff | sed "other stuff" At the very end or after the curl?
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6answers
3k views

how to beep on tail -f event

I want my PC to make a system beep on every tail event I have the following command tail -f development.log | grep "something rare" is there an easy way like pipeing it to somthing that beeps? ...
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53 views

Multiple grep command and show after line

I have this command grep -iE -A18 "$(date +"%Y-%m-%d").*error" * | grep -v -A18 'Movig to Error Queue' but the result shows me the 18 line after 'Moving to Error Queue' but I do not want that. I ...
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6answers
3k views

What is the general consensus on “Useless use of cat”?

When I pipe multiple unix commands such as grep, sed, tr etc. I tend to specify the input file that is being processed using cat. So something like cat file | grep ... | awk ... | sed ... . But ...
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3answers
4k views

How to pipe awk output (with periodic, continuous input) to output file?

I am trying to write a command that pipes the continuous output of a free command (run every second) to an awk command that parses a specific value (available free memory) and outputs this to a file ...
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1answer
77 views

Linux - Output to Folder that Yet Exists (in one command)

Is it possible to achieve this in one command without requiring a script: echo "test" > /folder/that/does/not/exist/newFile.txt
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1answer
230 views

Use 'find' command to search for PNG files, pipe output to imagemagick for batch conversion

I've got a directory with thousands of image files, mostly JPG but some PNG. The files have no extension, they're just numbered. I need to convert all of them to JPG. Using find I can get a list of ...
3
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1answer
102 views

Using pv(1) to limit rsync speed

I'm trying to use pv rather than rsync's builtin --bwlimit to limit the bandwidth of an rsync transfer because --bwlimit is implemented in an eventually-consistent way, and my transfers are so short ...
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2answers
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Why is piping 'dd' through gzip so much faster than a direct copy?

I wanted to backup a path from a computer in my network to another computer in the same network over a 100 Mbit/s line. For this I did dd if=/local/path ...