Tagged Questions
2
votes
1answer
38 views
broken pipe error with popen and JS ffi
I am using a ffi for nodejs which for the most part has nothing to do with this question which is really about understanding pipes better, but does offer some context
function exec(cmd) {
var ...
2
votes
1answer
54 views
redirection to file issues with nohup and pipe
For the following command:
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
38 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 ...
3
votes
4answers
111 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
3answers
116 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
37 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 ...
3
votes
2answers
82 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 ...
1
vote
1answer
64 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 ...
2
votes
1answer
77 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 ...
1
vote
2answers
71 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.
2
votes
4answers
293 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
89 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
4answers
116 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 ...
2
votes
1answer
174 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
452 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
432 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
84 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?
2
votes
2answers
194 views
Mplayer controls when using stdin playlists
I ran across this post: How can I retain the console input in mplayer when reading from stdin?
But the answer there doesn't work for me. (and I can't comment due to not enough rep)
I'm running the ...
16
votes
3answers
2k views
How to make bidirectional pipe between two programs?
Everyone knows how to make unidirectional pipe between two programs (bind stdout of first one and stdin of second one): first | second.
But how to make bidirectional pipe, i.e. cross-bind stdin and ...
7
votes
2answers
175 views
How a piped shell programs balance their output/input rates? [duplicate]
Possible Duplicate:
Bash while loop and reading from pipe
I come from web programming background, and find myself interested in one peculiarity of using a local shell. I understand that ...
2
votes
3answers
422 views
Bash while loop and reading from pipe
I have a Windows command-line program that I'm running in a Bash script in Ubuntu via wine. The Bash script basically looks like this:
wine myprogram.exe | while read line
do
# Process line
done
...
3
votes
2answers
1k views
Bash: How to read one line at a time from output of a command?
I am trying to read the output of a command in bash using a while loop.
while read -r line
do
echo "$line"
done <<< $(find . -type f)
The output I got
ranveer@ranveer:~/tmp$ bash ...
20
votes
6answers
1k views
Why can't I redirect a path name output from one command to “cd”?
I am trying to get cd to accept a directory name redirected to it from another command. Neither of these methods work:
$ echo $HOME | cd
$ echo $HOME | xargs cd
This does work:
$ cd $(echo $HOME)
...
4
votes
3answers
278 views
How can I do the equivalent of tail -f with ls? [duplicate]
Possible Duplicate:
Is it possible to follow a command (run repeatedly)? as one would follow a file using tail -f?
I would like to monitor files that are being downloaded to a directory in ...
21
votes
1answer
673 views
Why does echo >file use more real time than echo | sed >file?
The example, below, surprised me. It seems to be counter intuitive... aside from the fact that there is a whisker more user time for the echo | sed combo.
Why is echo using so much sys time when it ...
3
votes
3answers
319 views
Using CSV line as command parameters
I have a CSV file like:
Name,Age,Address
Daniel Dvorkin,28,Some Address St. 1234
(... N ...)
Foo Bar,90,Other Address Av. 3210
And I have a command that take this parameters:
./mycommand ...
3
votes
3answers
94 views
How to include program which only works with in/out files into a pipeline?
I need to process image with several tools in a pipeline tool1 | tool2 | tool3 | .... It appeared though that one of the tools isn't designed to work in a pipeline and only works in format of ...
1
vote
1answer
110 views
Magic file that redirects to standard output
Is there a magic file name that gives the following effect?
$ mkfifo /tmp/fifo1 && cat /tmp/fifo1 &
$ foo --log-file /tmp/fifo
# now I can see the log as the program runs
I want ...
3
votes
1answer
129 views
How can I pipe a path to pushd?
This seems like it should be easy enough to do, but I'm clearly not understanding something fundamental about piping output back and forth.
I'm trying to do something like this:
bundle show ...
6
votes
4answers
225 views
How can I print a conditional header BEFORE stdout, if there is any output on stdout
I have a process that filters a list of files from a directory (having find check to see if there are files older than a certain period to show a queue is stuck). It may or may not return anything, ...
4
votes
1answer
2k views
How to check if pipe is empty
I have piped line in bash script and want to check if pipe has data, before feeding program
Searching I found about test -t 0 but it doesn't work here. Always returns false.
So how to be sure that ...
4
votes
3answers
240 views
How to pipe to multiple places with vertical bar?
I have a folder full of files with a .dot extension like this:
a.dot
b.dot
c.dot
I want to go through all the files in this folder and run a command on them such as this:
dot -Tpdf a.dot -o a.pdf
...
4
votes
2answers
516 views
Using files that have spaces in their name in pipes
I have folder named play which contains a file damn file (with space). When I use find and pipe the output to tar:
find play/ -name 'damn*' | tar cf archive.tar -T -
It works perfectly. Why does ...
5
votes
2answers
2k views
what is meant by connecting STDOUT and STDIN?
This is a newbie question. I'm reading a book, it says:
Every process has at least three communication channels available to it: “standard
input” (STDIN), “standard output” (STDOUT), and ...
4
votes
2answers
213 views
How to expand tabs based on content?
I've got some tab-delimited data coming out of a Unix pipe. I'd like to format this data into a compact human-readable table.
How can I expand these tabs into spaces, and automatically set the tab ...
5
votes
5answers
2k views
Shell Script mktemp, what's the best method to create temporary named pipe?
I'm aware its best to create temporary files with mktemp, but what about named pipes?
I have an idea, I'm sure it would work,
but I would really like an expert opinion.
I prefer things to be as ...
3
votes
1answer
337 views
ssh “-f” don't give back hand in bash when listening to stdout/stderr
Please look at these:
## Does NOT return to the shell, but Ctrl-C can exit
ssh -S none -fNR 13018:localhost:22 example.com | cat
## Returns to the shell (no "-S none")
ssh -fNR ...
6
votes
1answer
457 views
Readable comments on separate lines in a multi-line bash command with pipelines?
When creating shell scripts using pipelines, and using the backslash to continue lines, I want to insert comments on separate lines, in a robust, readable and portable fashion.
For example, given ...
3
votes
3answers
588 views
Create a temporary file from a stdout redirect or pipe
Some commands only output to stdout.
Some tools only work on files.
Is there a command that can glue those together?
Contrived simple example:
diff $(echo 1 | stdout-to-temp-file) $(echo 2 | ...
2
votes
2answers
557 views
Difference between > and | with /dev/tty
When I run this command:
echo "1" > /dev/tty # runs successfully
but when I run this:
echo "1" | /dev/tty #permission denied
What is the difference between these two operators > and | and ...
8
votes
4answers
4k views
Difference between 2>&1 > output.log and 2>&1 | tee output.log
I wanted to know the difference between the following two commands
2>&1 > output.log
and
2>&1 | tee output.log
I saw one of my colleague use second option to redirect. I know ...
2
votes
3answers
998 views
How to feed the results of date command into grep to filter results of another command
I need to use the result of a formatted date command (date +"%m/%d") as the grep filter to filter the results of another command that will display alerts on a system so that I only see alerts from the ...
14
votes
4answers
1k views
How to understand pipes
When I just used pipe in bash, I didn't think more about this. But when I read some C code example using system call pipe() together with fork(), I wonder how to understand pipes, including both ...
6
votes
2answers
412 views
Piping output from a segfaulting program
I have a script that calls a program (specifically, ttf2afm, part of tetex 3.0) that sometimes segfaults and sometimes doesn't. The information I need is always printed out before it segfaults, but ...
15
votes
4answers
1k views
Process substitution and pipe
I was wondering how to understand the following:
Piping the stdout of a command into the stdin of another is a powerful
technique. But, what if you need to pipe the stdout of multiple
...
5
votes
2answers
510 views
redirection and pipeline
I was wondering about differences and relation between redirection and pipeline.
Is pipeline only used to connect
stdout output of a command to stdin
input of another command?
Is redirection only ...
4
votes
1answer
635 views
How to pipe the result of 'date' command to 'mv' command
I want to rename my file to the current timestamp.I know how to get the current timestamp("date +%s") but how can I pipe it to 'mv' command?
24
votes
11answers
6k views
Get exit status of process that's piped to another
I have two processes foo and bar, connected with a pipe:
$ foo | bar
bar always exits 0; I'm interested in the exit code of foo. Is there any way to get at it?
8
votes
5answers
2k views
How to pipe output from one process to another but only execute if the first has output?
How can I rewrite this command to only email if there is output from the mailq | grep?
mailq | egrep 'rejected|refused' -A 5 -B 5 | mail -s 'dd' email@email
Is this even possible on one line?
5
votes
1answer
259 views
I'm confused as to why “| true” in a makefile has the same effect as “|| true”
I have a makefile where I'm stopping a service before removing a file. When it couldn't stop the service, it would break on error. This is clearly unwanted so I thought I'd add || true but missed a |. ...
