Tagged Questions

2
votes
1answer
34 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
1answer
112 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
90 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 ...
0
votes
1answer
101 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 ...
4
votes
3answers
125 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 ...
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 ...
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
333 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
122 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 ...
2
votes
2answers
140 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
246 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 ...
6
votes
1answer
234 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 ...
1
vote
0answers
134 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 ...
5
votes
2answers
262 views

Pipe Password to Application When Asked

The following should be done in a bash script: curl --digest --user schmijos https://bitbucket.org/u/p/get/tip.zip -o tip.zip How can I automatically submit a password to curl when it asks for it? ...
3
votes
2answers
842 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 ...
4
votes
2answers
258 views

Passing parsed output of sed to find (in this direction)

Well, I think you can find dozens of questions on this platform how to pipe find output to sed, but I haven't found anything for the reverse direction so far. What I want to do is modify my input, and ...
3
votes
2answers
476 views

How do I use tee to redirect to grep

I don't have much experience of using tee, so I hope this is not very basic. After viewing one of the answers to this question I came across a strange beheviour with tee. In order for me to output ...
0
votes
1answer
155 views

The “cp p2 &2 &” command makes Konsole to disappear, is it a bug?

The goal is start a background process that copies the data from the pipe p2 to the STDOUT as p2 is feed with data by some other process. I guess the command is incorrect. Nevertheless, the Konsole ...
20
votes
1answer
655 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 ...
79
votes
2answers
3k views

Bash: What does “>|” do?

I have just seen this written down; $ some-command >| /tmp/output.txt Vertical pipes are used in standard redirects "piping" the output of one command to another, is >| in fact completely ...
7
votes
3answers
1k views

Using in/out named pipes for a TCP connection

I've been fiddling with getting this to work for a while now, so I suspect some sort of fundamental misunderstanding about how pipes work is the root cause of my troubles. My goal is to initiate a ...
7
votes
4answers
555 views

What is the easiest way to execute text from tail at the command line?

Sometimes I'm working on a new (ubuntu) box and I type git and am alerted: The program 'git' is currently not installed. You can install it by typing: apt-get install git-core If that happens I ...
5
votes
2answers
1k views

Running piped bash script in background

I'm attempting to build a monitoring script to watch localhost communication using netcat. I have two scripts that I've built, one to start the monitoring loop and one for the loop itself. They are as ...
3
votes
3answers
683 views

How can I pass output of one command as an argument to another

A similar question has been asked, but since I am new to Unix the answer was not clear to me due to the context. What I want to do is to pass the output of one command as an argument to another. I am ...
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 ...
6
votes
3answers
1k views

Have Bash script wait for status message before continuing

I'm firing up Selenium server with a bash script and as you can see from the timestamps on the log below, it takes about 32 seconds for the thing to fully come online: Feb 28, 2012 10:19:02 PM ...
2
votes
1answer
255 views

Keep global variables values piping through functions

I wrote a little bash script using sed on some html pages to extract some urls. To avoid each time grabbing sed results in a variable then read it again I simply made 3 functions and piped together. ...
5
votes
1answer
132 views

Confusion about sed and '>'

The following command works fine: sed s/input/raw_input/ p.py >p2.py && mv p2.py p.py However, the following command turns p.py into an empty file: sed s/input/raw_input/ p.py >p.py ...
6
votes
1answer
439 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 ...
2
votes
1answer
1k views

How to set a new password from bash?

I'm using busybox with a limited passwd (I don't have --stdin option) and without chpasswd and I need to change the password of an user from bash. Here is my best result: echo newpassword > ...
7
votes
3answers
364 views

Piping STDERR vs. STDOUT

According to "Linux: The Complete Reference 6th Edition" (pg. 44), you can pipe only STDERR using the |& redirection symbols. I've written a pretty simple script to test this: #!/bin/bash echo ...
4
votes
1answer
219 views

Pipes vs process substitution

While trying the cat "$@" trick to read from either standard input or given files, it turned out that pipe and process substitution handle a missing trailing newline differently: printf %s foo > ...
6
votes
2answers
917 views

bash: Piping for loop output prevents local variable modification

First off, sorry for the title. I'm not sure of the correct terminology so if anyone can improve upon it that would be good. I am trying to write a simple bash function that takes, as it's arguments, ...
1
vote
3answers
463 views

Ls with spaces + variables

I want to do something like this, but it doesn't save the variable after the piping ends: fs=( ) echo ${fs[@]} ls -A1 | while read f do echo ${fs[@]} fs+=( "$f" ) echo ${fs[@]} done echo ...
4
votes
6answers
1k views

Using data read from a pipe instead than from a file in command options

Per man definition, this command gets the input from a file. $ command -r FILENAME Suppose that FILENAME is a file containing a list of filenames, as it was generated using ls > FILENAME. How ...
2
votes
2answers
299 views

.DELETE_ON_ERROR behavior with make and pipelines

The .DELETE_ON_ERROR target will tell make to delete a target if a rule fails. But this doesn't work for pipelines, because the exit status value $? holds the value of the last program in the ...
2
votes
4answers
2k views

Passing pipeline value as parameter to xargs for use by eval echo

I have a text file that I'm using as a template, it looks like this: Hostname : $HOSTNAME Host Address : $HOSTADDRESS My bash script sets two variables, HOSTNAME and HOSTADDRESS, reads the ...
4
votes
3answers
2k views

Why is my variable being localized in one 'while read' loop, but not in another seemingly similar loop

Why do I get different values for $x from the snippets below? #!/bin/bash x=1 echo fred>junk ; while read var ; do x=55 ; done <junk echo x=$x # x=55 .. I'd expect this result x=1 cat ...