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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Howto pipe: cp | tar | gzip without creating intermediary files?

Can anyone tell me if it's possible to pipe | this without having to create a physical file anywhere between A and B.tar.gz? This is what I'm trying to do: File A Rename A to B Tar B.tar gzip -9 ...
3
votes
1answer
2k views

How long do FIFOs (named pipes) stay “open” for?

For example, I have a script that writes the time to a pipe in /etc/pipe. It writes continuously in a while true loop. How long will the data in the pipe be available for reading? If I only decide to ...
12
votes
3answers
17k views

Passing two arguments to a command using pipes

Usually, we only need to pass one argument: echo abc | cat echo abc | cat some_file - echo abc | cat - some_file Is there a way to pass two arguments? Something like {echo abc , echo xyz} | cat ...
3
votes
1answer
4k views

Sniff process communication on Windows 7

I have two local processes which communicate to let the other execute commands. And I want to know what they are talking about. After some first investigation, it's not over Sockets or Loopback, but ...
1
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2answers
4k views

How to feed grep output into scp?

I have a file where each line is a file name. Content of the file: file1 file2 file3 ... I then run a grep command to get a subset of the list of the file names. How do I feed the output of the ...
2
votes
1answer
89 views

Which is better: using flags, or pipes?

As with many things in the *nix world, there is more than one way to generate .tar.gz files. Typically, I use the following: tar zcf /path/to/dir.tar.gz /path/to/dir However, I have seen the ...
3
votes
3answers
1k views

Pipes, shell scripts and ulimit

I have a command that I'm calling from code: execvp('generate', ...) which is an executable program that my code communicates with via stdin, stdout and stderr. This works fine, not a single ...
12
votes
5answers
7k views

What is a “pipe” and how can it be “broken”?

I've gotten the "broken pipe" error from Xcode one time too many. I'm now curious to know exactly what a pipe is. What is the concept of a "pipe" and how can it be "broken"?
0
votes
1answer
33 views

Piping results back into the program that generates them

I've got a program that can take input from stdin and produces output in the stdout like this: cat initial_input.txt | myprogram myindex myoptions - | filter_output > outfile.txt The program ...
1
vote
2answers
1k views

Pipe screen buffer to another command?

I can't seem to find anything on this so, is there a way to pipe everything from a screen window into another command. I have a server running in screen (not the best idea, but the only way for the ...
57
votes
6answers
12k 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 ...
2
votes
1answer
236 views

Is there any way to pipe local output to an SSH server as well?

Is there any way to set up a local process, but have the output also go to a terminal that has SSH'd into my machine?
3
votes
1answer
748 views

Linux: redirecting stdout and stderr

I want to write stdout to a file but also prints stdout and stderr. I tried using tee: prog | tee stdout.txt but this causes the printed stderr and stdout to be interleaved incorrectly, i.e. if the ...
9
votes
1answer
1k views

Is backwards redirection the same as a pipe?

In Linux if you type sort < txtfile is that the same thing as cat txtfile | sort
6
votes
1answer
6k views

Is it possible to pipe a list of files to RMDIR on Windows?

I am writing a batch file for the Windows command prompt to delete all directories matching a certain expression. I am first using DIR to return a plain list of directories matching the expression. I ...
2
votes
2answers
4k 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 ...
1
vote
2answers
2k views

Split a large .gz file and gzip each of split file?

I have a large text.gz file (2GB) and I want to split it by line. I tried to use: zcat text.gz | split -l1000000 However this generated a huge file (around 92GB before I terminated it) and put too ...
13
votes
1answer
9k views

how to escape pipe symbol | in bat scripts?

I need to echo commad usage like this in batch script named command.bat command.bat on|off I cant use echo %0 on|off I know I can use echo "%0 on|off" but it puts quotes along Is there any ...
3
votes
3answers
1k views

Linux: Limiting data throughput (pipe) in bytes per second?

I was wandering if there is a Linux program that can limit data throughput of a pipe - in actual bytes per second?. From what I gather, applicable for the purposes would be bfr, however, it has ...
6
votes
2answers
2k views

How do you determine the actual command that is piping into you?

Let's say I have a bash script called log.sh. In this script, I want to read in input from a pipe, but I also want to know the command used to pipe input into me. Example: tail -f ...
0
votes
1answer
616 views

OS X: log text from serial port

I have a text stream coming in on a USB-RS232 adapter. I want to pipe it to some Unix tools, to a file, whatever. What is the simplest way to do so? Does it really require third-party software? OS X ...
5
votes
3answers
4k views

Windows how to redirect file parameter to stdout? (Windows equivalent of `/dev/stdout`)

Windows console: Tool A can write binary data to a file, but has no option for telling it to use stdout. Tool B can read binary data from stdin and process the info in it. How can I get the output ...
12
votes
3answers
5k views

Comments in a multi-line bash command

This single-command BASH script file is difficult to understand, so I want to write a comment for each of the actions: grep -R "%" values* \ | sed -e "s/%/\n%/" \ | grep "%" \ | grep -v " % " \ | ...
2
votes
4answers
5k 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 ...
3
votes
1answer
6k views

Pipe/send command to process running on nohup that accepts input from STDIN

I have a program that I run using nohup program &. This program accepts input from STDIN. Is there any way to send text to the STDIN of a program that is running via nohup? This is on FreeBSD ...
6
votes
2answers
3k views

monitor interprocess pipe traffic

I have two Linux processes communicating via a nameless pipe. How can monitor the traffic in the pipe? How can I inject data into the pipe? I have root access and know the pipe inode.
1
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1answer
1k views

pipes & tail -f in linux

Is it possible to execute cat logfile | tail -f? For some reason it just reads the initial log, but then it doesn't update incoming entries. I know I can directly do tail -f logfile. I just wanted ...
0
votes
3answers
333 views

Command output redirection to vim not working on OS X

I'm trying to redirect the output of a command to vim using the - argument, but it doesn't seem to work on OS X. For example, if I type $ ls | vim - on the command line on one of my Linux ...
12
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6answers
5k views

Make a pipe conditional on non-empty return

Is there a way to pipe the output of one function to another, but only if there is an output?
3
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2answers
6k views

How to sort ls by column in Ubuntu via piping to sort?

I'm a Linux newbie trying to learn how piping works in the Ubuntu terminal. I tried to sort by file size: ls -al | sort -k5 The files were listed in this order: drwx------ 19 min10 domain users ...
8
votes
4answers
16k views

Why does this not work? “ls *.txt | xargs cat > all.txt” (all files into single txt document)

Why does this not work? ls *.txt | xargs cat > all.txt (I want to join the contents of all text files into a single 'all.txt' file.) find with -exec should also work, but I would really like to ...
1
vote
2answers
1k views

pipe a program into less

I'm taking the dive into setting up and learning git and at the same time learning bash. I'm trying to do something simple as view the help section of $ git config unfortunately, when I type that ...
13
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7answers
10k views

Advantages of cat'ing file and piping to grep

Are there any additional advantages of cat'ing a file and piping it to grep, besides convenience? The convenience being that, when I retrieve commands such as those below from my history, the cursor ...
45
votes
4answers
68k views

How to pipe command output to other commands?

Example: ls | echo prints nothing ( a blank line, actually ). I'd expect it to print a list of files. ls | grep 'foo', on the other hand, works as expected ( prints files with 'foo' in their name ). ...
12
votes
4answers
8k views

Bash: create anonymous fifo

We all know mkfifo and pipelines. The first one creates a named pipe, thus one has to select a name, most likely with mktemp and later remember to unlink. The other creates an anonymous pipe, no ...
2
votes
1answer
783 views

How do I run a command on each file within a directory that matches a pattern?

I'm trying to run a command on every file within a directory (recursively) that matches a pattern. I need the filename of each item that matches for the command however. This is how far I've got: ...
1
vote
2answers
744 views

Split an[d] archive large backup file in constant working space

I'm currently attempting to use tar and split to get DVD-sized archives of my Time Machine backup database. It's going to work this time, as I have a partition on my external drive large enough to ...
23
votes
4answers
30k views

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 ...
4
votes
2answers
425 views

How to utilize vim's syntax color to replace the `highlight' utility?

I feel that the `highlight' utility doesn't support as many file types as vim does, and the project isn't very active. When the file is gzipped, highlight doesn't recognize it at all. But in ...
4
votes
1answer
2k views

Pipe grep exit code away

When I need to suppress some kind of output e.g. foo | grep -v bar But foo gives sometimes only: bar bar bar... grep will return -1. How do I transform the exit code 1 to 0?
2
votes
4answers
5k views

Rsync to stdout?

I have access to backup server via rsync protocol (only rsync, nothing else). Now, I want to fetch file from there (which is .tar.gz) and pass it directly to tar command, without saving the archive in ...
1
vote
3answers
1k views

Double pipes in Linux

Is it possible to do a command in Linux with "double pipes", like this? blah | blah | blah
2
votes
1answer
114 views

How to construct shell redirection on command line

Consider the following command in Unix: echo 0123456789 | cat >/tmp/foo &> /tmp/bar The echo is sent to /tmp/bar. However, what I really want is to redirect the stdout and stderr output ...
3
votes
2answers
2k views

gpg symmetric encryption using pipes

I'm trying to generate keys to lock my drive (using DM-Crypt with LUKS) by pulling data from /dev/random and then encrypting that using GPG. In the guide I'm using, it suggests using the following ...
1
vote
1answer
622 views

grep -v -A not working properly (actually not working at all)

I have to filter lines like the following: [javac] /Users/looris/Sviluppo/android/projects/toutry/src/net/looris/toutry/Stuff.java:23: warning: unmappable character for encoding ascii [javac] ...
4
votes
5answers
855 views

commands executing in piping in UNIX

when I write a command $ echo date then it prints "date" as it is i.e it doesn't run date program. But when I write $ echo date | wc then correct answer is produced as if date was run. How ...
40
votes
2answers
8k 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 | ...
3
votes
1answer
755 views

Unix commandline to repeat command with pipes

I want to write a script that will repeat a commandline that usually contains pipes ./myscript.sh ls -lart |grep ^d And in myscript.sh I do a bunch of stuff, and then want to execute ls -lart |grep ...
1
vote
1answer
1k views

Making nano accepting previous piped output as a file path

When I run the following command in linux: find / -iname httpd.conf I get: /usr/local/apache/conf/httpd.conf I want to use nano to edit this file, lazy to type the file path again, I used: find ...
0
votes
2answers
999 views

Grepping grep output fails

I'm trying to grep the output of ngrep. Unfortunately when I add another grep to the pipeline, I get no output at all. It can be some other command too - cat / grep / tee - everything breaks the ...