Chains the standard streams of a series of commands
1
vote
2answers
22 views
Variable scope in multiple pipes
I was trying to do something following,
find . -name "*.dat" | get the basename of file | move filename returned by first command to basename returned by second command
To give a concrete example, ...
2
votes
2answers
58 views
Are FIFO, pipe & Unix domain socket the same thing in Linux kernel?
I heard that FIFOs are named pipes. And they have exactly the same semantics. On the other hand, I think Unix domain socket is quite similar to pipe (although I've never made use of it). So I wonder ...
7
votes
1answer
138 views
“w | tail” chops text at right margin (78 characters)
Summary: w | tail chops rows after 78th column.
When I run the "w" command, it works as expected. However, when I pipe the output to "tail", it chops the output to 78 columns wide (truncates anything ...
4
votes
3answers
66 views
Can I pipe any two processes to each other?
In this page from The Design and Implementation of the 4.4BSD Operating System, it is said that:
A major difference between pipes and sockets is that pipes require a
common parent process to set ...
-2
votes
0answers
45 views
pipe() is not working well [closed]
I'm trying to make a program using the pipe communication. This is what I'm trying to do: the user sends positive integers. If the user sends a negative number the communication ends. The parent ...
2
votes
1answer
35 views
redirection to file issues with nohup and pipe
for the following script
ssh -t esolve@hostname 'sudo nohup bash -c "ls > log 2>&1 &"'
I always got error information:
nohup: ignoring input and appending output to ...
2
votes
1answer
36 views
process continous output of synclient
I am using synclient to track the position of finger on the touchpad.
I use the following command.
synclient -m 100 | awk '{print $2,$3}'
This command gives the 'x' and 'y' co-ordinate on the ...
4
votes
2answers
63 views
Who cuts off first symbol of process substituted file and for what reason?
$ type 1.sh
#!/bin/bash -eu
php <(echo 12)
$ ./1.sh
2
$ type 2.sh
#!/bin/bash -eu
cat <(echo 12)
$ ./2.sh
12
$ type 3.sh
#!/bin/bash -eu
echo 12 | php
$ ./3.sh
12
$ type 4.sh
#!/bin/bash -eu
...
3
votes
1answer
49 views
How can I copy a file between server using bsdtar?
I'm looking for the fastest way of copying a file between 2 linux servers using bsdtar.
With normal tar, I would do something like:
ssh root@remote 'tar -cz -C /my/path/ big_file.txt' | tar -zxv
...
0
votes
2answers
121 views
Redirecting stdin with stdout to file
So I have a program that takes in user input and outputs text based on the input.
EDIT2: I want to create a script that runs a C executable and the script feeds the C program input from a file and ...
3
votes
4answers
81 views
Getting stdin from a named pipe
What I am trying to do is run python in a terminal window and redirect it's stdin from a named pipe. Then I write to the named pipe in another terminal and have that command execute on python.
...
3
votes
1answer
118 views
Pass colors from ls through pipe to awk 'print' statement
This is a follow-up to my question from yesterday, Show sum of file sizes in directory listing.
Thanks to Zero Piraeus and a point in the right direction by Mauritz Hansen, I now have
function ...
3
votes
3answers
94 views
Can't process stdout with pipe as it comes
I'm running tshark on a fifo, and the following is a bare example of a loop that prints the output of tshark as it comes:
tshark -i $fifo | while read line; do
echo $line
done
The problem ...
3
votes
2answers
33 views
How to duplicate a stream and process both parts in a streaming way?
Sometimes I want to insert something in a pipeline for reporting or some other secondary use. It might be as simple as wc -l, or a more complex beast like awk or even a python script. It'd be nice to ...
2
votes
3answers
88 views
Output to stdout and at the same time grep into a file
I have a script that outputs text to stdout. I want to see all this output in my terminal, and at the same time I want to filter some lines and save them in a file. Example:
$ myscript
Line A
Line B
...
3
votes
1answer
93 views
background process pipe-input
if i want to display "aaa" on screen:
(1)$: echo aaa | cat ... works OK
(2)$: echo aaa | ( cat ) ... works OK
(3)$: echo aaa | ( cat & ) ... NOT working
...
0
votes
3answers
67 views
pass piped variable to perl oneliner
if you have something like:
find . -d -maxdepth 1 | wc -l | perl ...
what ways do you have to tell perl to take this variable that's coming its way and substract 1?
I try to substract 1 since find ...
2
votes
2answers
92 views
Does one end of a pipe have both read and write fd?
As far as I understood one end of a pipe has both read and write fd's and the other end also has read and write fd's. Thats why when we are writing using fd[1], we are closing the read end e.g. ...
3
votes
2answers
69 views
Read data from a pipe for a certain amount of time (in seconds)
Is there an easy way to create a pipe that only lasts for a given amount of wall time?
I want to be able to take a "snapshot" of what's being written STDOUT for a period of time (rather than bytes or ...
0
votes
1answer
110 views
ps | grep shows bad output in subshell with jobs running in the background
I am using bash. I have a file named "a2draw" that contains only 1 line:
sleep 99999
I start it using this command:
bash a2draw &
Now, I know and understand the trick with square bracket ...
1
vote
0answers
131 views
avconv/ffmpeg output through /dev/ttyAMA0
I tried to pipe streaming video from video4linux2 webcam connected to a Raspberry Pi through /dev/ttyAMA0 to a computer using an Arduino as a intermediary. First of all, is it possible? Because I was ...
21
votes
2answers
1k views
What are the advantages of using named pipe over unnamed pipe?
I was reviewing a set of interview questions that are asked from a unix admin; I found a topic called "named pipe".
I googled the topic; to some extent I have been able to understand it :- named ...
4
votes
3answers
130 views
Races when piping two commands to a named pipe
I want to have one process reading from a named pipe that receives data from multiple sources:
$ mkfifo /tmp/p
But I can't figure out how to get it to work consistently.
First Scenario - this ...
0
votes
1answer
145 views
Can someone provide an xargs example piping mysql query data into another command?
Can someone provide an example for the command xargs? I want to do a mysql query to return the ID field of a column then feed that result into xargs into another command say mysql query delete. How ...
1
vote
1answer
61 views
What rules govern the parent-child relationship of processes launched by shell across a pipe?
#!/bin/ksh
# start_service: start the service
my_server_executable 2>&1 | my_pipe_following_shell_script &
exit 0
After I run the above start_service script from command line, it is ...
9
votes
1answer
193 views
What are guarantees for concurrent writes into a named pipe?
For example, I created a named pipe like the following:
mknod myPipe p
And I read from it from some process (for example, some server). For example purposes, I used tail:
tail -f myPipe
If ...
3
votes
4answers
175 views
Piping output to text file within a for loop
I'm trying to do the following within a for loop:
Find files that satisfy a condition
Echo the name of the files to a log file.
Gzip the file.
I can get the script to find the files and echo their ...
1
vote
1answer
39 views
Encrypting import's output with gpg at the same time
The import command saves screenshot in a file. Is there a way to encrypt that file at the same time using gpg, without saving the image file first? gpg accepts input from stdin but it seems that ...
3
votes
3answers
147 views
tee + cat: use an output several times and then concatenate results
If I call some command, for instance an echo I can use the results from that command in several other commands with tee. Example:
echo "Hello world!" | tee >(command1) >(command2) ...
4
votes
0answers
66 views
Combing head and tail in a single call via pipe [duplicate]
On a regular basis, I am piping the output of some program to either head or tail.
Now, suppose that I want to see the first AND last 10 lines of piped output, such that I could do something like
...
1
vote
2answers
129 views
Why does pipe not work with cat and locate?
I am trying to perform this:
locate pg_type.h | cat
But this command simply does nothing different than locate pg_type.h
What should I change ? I want to perform cat pg_type.h wherever pg_type.h ...
2
votes
1answer
73 views
Stderr of piped shell scripts isn't always displayed
I piped my own shell scripts for some testing and accidentally noticed something strange. Namely, the stderr of those piped processes isn't always displayed on the screen.
I simplified the scripts ...
2
votes
1answer
352 views
Bash vs ksh pipes
I am stuck with some problems with my scripts in ksh. FWIW the problem which I am unable to overcome is that when I use a structure such as this
command | while read VAR1
do
many.commands using ...
1
vote
3answers
133 views
How to stop `grep` from truncating pipe output
Is there any way to have an echo at the end of a pipe simply append to the current output rather than removing it all? For example, how can I keep the output for my cat and grep and add "END OF ...
1
vote
2answers
70 views
Piping commands together in unix
How do I pipe the output of one command to another in unix? For example,
If I want to pipe the output of sort to tail, how would I do that?
Thanks in advance.
1
vote
1answer
92 views
Managing the output streams of many subprocesses with deadlocks
I have a Python script that does more or less this
current_tasks = TaskManager()
MAXPROCS = 8
while len(outstanding_tasks) > 0:
if len(current_tasks.running) < MAXPROCS:
...
2
votes
2answers
146 views
Pseudo files for temporary data
I often want to feed relatively short string data (could be several lines though) to commandline programs which accept only input from files (e.g. wdiff) in a repeated fashion. Sure I can create one ...
2
votes
4answers
252 views
How to pipe the stdout to a file if the current command is already being piped through gzip
So I have this command I need to run then disown:
innobackupex-1.5.1 --user=root --password=**** --stream=tar ./ | gzip - > /data/myfile.tar.gz
How do I pipe any output to a file?
adding ...
3
votes
1answer
44 views
Emulating a file
I have certain application that opens a file with given path (presumably with fopen or derivative), reads the file, possibly writes to it and closes it. I have no control over this application other ...
3
votes
1answer
85 views
No output from inotifywait | awk
I'm attempting to use part of a one-liner found here: Script to monitor folder for new files?
When I try the following procedure I get no output whatsoever and I cannot figure out why.
In terminal ...
2
votes
1answer
113 views
How to copy the output of pacman-color into a file and to display the output with the colors in the terminal
Originally I used pacman, not pacman-color and I copied the output into a file and I displayed the output in the terminal with the following command :
pacman -Syu | tee file.log
Unfortunately, it ...
3
votes
2answers
270 views
Why does Subversion give a broken pipe error when piped into head?
If I do a
svn log | head
after the tenth line of output I get an error message:
svn: Write error: Broken pipe
What's going on here? I haven't seen any other command do this when used with head. ...
2
votes
4answers
114 views
store and execute redirection/piped command in script
How do you store, and later execute, a command with redirection and and a pipe? (And is it the pipe, or the redirection, or both, that's causing my problem?)
I tried to print the urxvt version in a ...
6
votes
1answer
246 views
echo vs <<<, or Useless Use of echo in Bash Award?
By now the Useless Use of cat Award is very well known, and there's also a mention of a Useless Use of echo (not relevant for this question). I'm wondering if there should be a "Useless Use of echo in ...
4
votes
1answer
287 views
Ksh loses data after piping 16K bytes
I recently found that ksh may lose some data after printing more than 16K bytes to the stdout if it is blocked for a couple of seconds.
This test.sh script prints out 257*64 (16448) bytes:
...
1
vote
0answers
136 views
Why does this pipeline get SIGTTIN?
When I run the command for i in *.log; do cat "$i" | sort; done | more, the pipeline gets a SIGTTIN signal and is stopped.
bash$ for i in *.log; do cat "$i" | sort; done | more
### (one screenful of ...
2
votes
1answer
158 views
Make stdout and stderr be buffered by the same buffer
Is it possible to force glibc to use the same buffer for stdout and stderr?
If I tee the both outputs:
./tests/tests 2>&1 | tee log
I get mixed messages (i.e. messages are ordered inside ...
4
votes
1answer
425 views
How to copy from/to the tmux 'clipboard' with shell pipes?
When working in a shell environment I run fairly often into the need to copy 'intermediate pipe output' around (eg. from/to already running editors, to other shells, other machines, etc.).
When in a ...
2
votes
3answers
364 views
Count running processes using wc and ps
I tried using ps r > log | wc log but this returns Ambiguous output redirect..
Can someone explain why and provide another solution?
1
vote
1answer
83 views
What is the difference between who > lp and who | lp?
Why does the who > lp creates a file but who | lp leads the output to program lp?
What is the underlying principle behind these two simple commands?
Can somebody explain it with an example?
