Chains the standard streams of a series of commands

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4
votes
0answers
48 views

How come zipping a created disk image, makes smaller files than piping?

Case 1. I use dd to create an image: dd if=/dev/rdiskx of=/path/to/image bs=1m. It's 16 GB in size. I zip it, and it's suddenly around 100 MB. Case 2. I use dd to create an image, piping it ...
5
votes
2answers
67 views

“command | less” vs “less <(command)”

A common "idiom" for viewing large amounts of command output is to pipe it to less, via command | less. However, it's also possible (perhaps only in bash, haven't tested in other shells) to use the ...
3
votes
5answers
48 views

reading a list of lines from a file writing output to a utility

I have a file with a list of lines I want to read from another file. I want to output those lines to a utility (grep) that lets me read the entire line and pull information from it. The file with the ...
5
votes
2answers
64 views

How can I pipe stdout to another program?

I'm trying to setup a linter for my code and I only want to lint the coffeescript files that have changed in the current branch. So, I generate the list of files using git: git diff --name-only ...
3
votes
1answer
23 views

Can close() block?

For example, if you close a pipe or socket that still has data in its write buffer that hasn't been read by the process on the other end, does close() block until the data is read or the other process ...
3
votes
2answers
83 views

Get specific line from command output in awk

I have used pipeline to read specific record from impala shell.Here is what I got [cloudera@localhost ~]$ echo "select * from abc where key > 'a-26052014015400' limit 1;" | impala-shell Starting ...
3
votes
2answers
130 views

using “ifne” in Bash pipe

In my script, I am using the ifne utility from the moreutils package. The line can be simplified to the following: printf "asdf\n" | ifne cat - && echo "stream not empty" ifne only ...
7
votes
3answers
680 views

Why do some commands not read from their standard input?

I wonder what when we should use pipeline and when we shouldn't. Say for instance, to kill certain process which handling pdf files, the following will not work by using pipeline: ps aux | grep pdf ...
2
votes
3answers
14 views

Piping content with multiple spaces

I was attempting to copy files listed in a text file into a directory such as: cat files.txt | xargs -I{} cp "{}" ~/Desktop/temp However I noticed that some files would not copy over. The files ...
14
votes
2answers
1k views

How do I “cat and follow” a file?

A file is being sequentially downloaded by wget. If I start unpacking it with cat myfile.tar.bz2 | tar -xj, it may unpack correctly or fail with "Unexpected EOF", depending on what is faster. How to ...
4
votes
2answers
67 views

continuous reading from named pipe (cat or tail -f)

I have configured rsyslog to log certain log events to /dev/xconsole: *.*;cron.!=info;mail.!=info |/dev/xconsole /dev/xconsole is a named pipe (fifo). If I want to see what is being logged, I ...
2
votes
2answers
70 views

Use output from head to copy files with spaces

I have 11 files with spaces in its name in a folder and I want to copy the newest 10. I used ls -t | head -n 10 to get only the newest 10 files. When I want to use the expression in a cp statement I ...
0
votes
1answer
40 views

eval used with piped command

I have file.txt with command stored in one line (this command is valid when running in console) and I want to execute it in one line with sh like cat file.txt | eval what is missing? any protips? ...
0
votes
2answers
46 views

How do I sort using the grep and sort command

I would like to create a sorted list of all TCP services found in the file /etc/services. Pipe the output of the command grep tcp /etc/services into the command sort. Redirect the output of this pipe ...
2
votes
3answers
60 views

Can I chain pgrep with kill?

I have noticed that | is used to send results of first command to the another. I would like to kill all processes that match a name. This is what pgrep normally does: $ pgrep name 5089 5105 And ...
2
votes
1answer
487 views

bottomless tee?

I was just playing around in the terminal and I did this: printf 'some string\n' | { tee /dev/fd/3 | { : && sed 's/some/string/' } } 3>&0 I was really surprised when ...
1
vote
1answer
61 views

upstart writing to syslog in a simple way

I have an upstart script that uses pre-start script exec >/dev/kmsg 2>&1 echo starting program # run my program here npm install node app.js end script to redirect output of a ...
0
votes
1answer
59 views

Pipe output from one command to another command's non standard input [duplicate]

I would like to do something similar to the following: which someapplciation | cd outputfrompreviouscommand The command which provides a directory and I would like to be able to make that output my ...
6
votes
3answers
257 views

Is it safe to pipe the stdout of A to B in parallel

I'm running A file | B --params > file.txt. Since I want to accelerate the processing speed, I used the parallel -j+0< a.txt to run 20 jobs concurrently. a.txt contains all the commands: A ...
1
vote
2answers
139 views

readarray (or pipe) issue

I stuck with an strange behaviour of readarray command. The man bash states: readarray Read lines from the standard input into the indexed array variable array but these scripts don't work ...
1
vote
1answer
63 views

Understanding behavior of subshell and stdout with pipe

Let us say I have .c file and corresponding executable (let us say foo) that takes in some input from stdin and then makes a sys call to /bin/sh. Feeding input to this executable like following: ...
3
votes
3answers
112 views

Environment variables are not set when my function is called in a pipeline

I have the following recursive function to set environment variables: function par_set { PAR=$1 VAL=$2 if [ "" != "$1" ] then export ${PAR}=${VAL} echo ${PAR}=${VAL} shift ...
1
vote
1answer
57 views

Send copy of a script's output to a file

Say I have a Zsh script and that I would like to let it print output to STDOUT, but also copy (dump) its output to a file in disk. Moreover, the script starts with the following option set -o xtrace ...
9
votes
1answer
314 views

communication between multiple processes

I have a bash script, which runs manager() function as a separate process for x-times. How is it possible to forward messages to all manager() processes from within the script? I've read about ...
15
votes
5answers
409 views

Is it possible to make zcat output text even if it's uncompressed? [duplicate]

The problem is I have some database dumps which are either compressed or in plain text. There is no difference in file extension etc. Using zcat on uncompressed files produces an error instead of the ...
1
vote
1answer
46 views

Use a bash function in a pipelined command

I have a command similar to: ... | sort -u -V. Since some versions of sort do not support the -V flag, I thought it would be great if I made a function that conditionally adds the flag. But, it seems ...
4
votes
1answer
83 views

Why do bash variables disappear when I use xargs?

I have a simple bash script and want to count how often a command gets called. Here is a minimal example, the counter is called c and should be 4 at the end: #!/bin/bash c=0; for a in X Y; do for ...
2
votes
3answers
90 views

Script needs to read echoed line

So, I need to write a Bourne-shell script, where my script has to work with the line, that was just echoed to stdout - e.g.: echo *something* | myscript.sh [parametres...] This may be a basic ...
1
vote
1answer
33 views

observing script execution with monit script seems to ignore pipes

I want to have a bash command running in the background and being watched by monit. To get the PID of this process, I found this script on the web and I modified it to fit my commands: (named sdr.sh) ...
6
votes
4answers
744 views

Why doesn't grep using pipe work here?

I have the following command: find / -name libGL.so.1 Which returns lots of lines with "Permission denied". I want to exclude such lines, so I added the following: find / -name libGL.so.1 | grep ...
4
votes
3answers
61 views

How to send SIGKILLs to entire pipeline?

while true; do # process substitution instead of usual pipeline to avoid waiting for all programs handle_input_with_timeout < <( prog1 | prog2 | prog3 ) echo "Data stopped flowing. ...
4
votes
2answers
131 views

Running several times the same command with several aguments after a pipe

I have a key (of random binary data) that gets generated by get_key. And with this key, I can do several things with my encrypted files. For example, I can decrypt them. get_key | tee >(decrypt ...
1
vote
1answer
31 views

Limiting readers on a pipe

I want to use a pipe to pass some security credential information from "process1" to another script. I only want authorized reader processes to be permitted to read the pipe. I am thinking I will ...
3
votes
1answer
83 views

Performance differences between pipelines and process substitution

I tend to use pipelines in my bash scripts over process substitution in most situations, especially in cases of using multiple sets of commands as it seems more readable to do ... | ... | ... over ... ...
22
votes
1answer
517 views

How do I redirect command completion output?

On the command line, I can redirect or pipe output of a command to a file or another command using the > or | operator after the command. I have come across a less standard situation that I would ...
1
vote
2answers
136 views

Output of command when piped to another command

I am running a command which does a quick checksum of some file like so find / -type f -ctime +30 -mtime +30 -atime +30 -exec md5sum {} \; | xargs -P 4 and I am trying to run it in parallel with ...
4
votes
1answer
141 views

Why doesn't colordiff work with stdin?

I have one file and one input coming from a pipe. They're identical. So why does colordiff report differences?: echo "123" | colordiff <(echo "123") - 1d0 < 123 It looks that this is ...
1
vote
1answer
65 views

Best way to determine piped command to shell script?

Given tree /some/directory | print.sh Is there any way for print.sh to know that "tree -f /some/directory" was called, without trying to parse pid processes?
4
votes
1answer
71 views

Does pipe's link target exist somewhere in the filesystem?

I'm talking about this: $ readlink <(echo test) pipe:[80076194] Is pipe:[80076194] a path to the target or just indication that the file descriptor is connected to the pipe and doesn't exist in ...
1
vote
3answers
135 views

how to pipe the output of cut to the foreach command?

I have the cut command I want that grabs the first word in each line of a file. I then want to put each word from the cut command into a foreach. I then want to do a grep command inside the body of ...
0
votes
1answer
58 views

Pipe doesn't read my forked script [closed]

I have a problem. I modified a script called 'packer' a AUR-helper for Arch Linux. The problem coming when I apply my pipe, with a progress bar, doesn't show all info as I need. This is my forked ...
2
votes
2answers
39 views

Output of one command is piped to another one; how to close both?

I call Qt Assistant like suggested on stackoverflow: nc -lkU ~/.assistantfifo | assistant -enableRemoteControl & Qt Assistant window is opened, and if I call jobs, it returns: [1] + running ...
1
vote
1answer
44 views

Pipe chain with devices

As far as I know, you can have the ability to make pipes between applications, such as this one: $ step1 < input_file | step2 | step3 > result_file And you can access devices such as ...
0
votes
2answers
103 views

bash function output to pipe [closed]

I made a bash function to beautify svn output, this function show logs one line per commit, it is great! I like it, but if I use it with pipe it does not work. You can find it on github svn-beautify ...
5
votes
3answers
224 views

How to read user input in pipe?

Let's assume I have a file named confirmation.sh with the following content: #!/bin/bash echo -n "Are you sure [Y/n]? " read line case "$line" in n|N) echo "smth" ;; y|Y) echo "smth" ...
2
votes
2answers
203 views

filter and count with grep in a single pass?

I am using grep at the end of a set of piped commands to filter some rows out of a file. Afterwards I will want to do some arithmetic based on the number of remaining rows. e.g. ...
6
votes
1answer
245 views

bash scripting - read tarball from stdin

I have a task I need to script that I feel should be stupidly simple, but I'm actually having a rather tough time. I have a short bash script that takes a specific type of application in tarball form ...
5
votes
1answer
260 views

Loop through binary data chunks from stdin in Bash

I'm looking for something like while IFS= read -r -n $length str; do ... done but for binary data. Is it possible to do this using dd or other tools? Is there some technique to make these tools able ...
7
votes
5answers
173 views

Can a program next in a pipeline see the exit code of the previous program?

I would like to make a pipeline of Bash scripts like this prog1 | prog2 such that prog2 can see the exit code of prog1 and act differently based on that information. Is this possible?
4
votes
5answers
227 views

Semi-asynchronous pipe

Assume I have the following pipe: a | b | c | d How to wait for completion of c (or b) in sh or bash? This means that script d can start any time (and does not need to be waited for) but requires ...