Chains the standard streams of a series of commands

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1answer
99 views

Very basic H/W question using pipe and grep

I have two text files, F1a.txt and F1b.txt, with essentially the same data: the driver's surname and their nationality. For example: Hamilton GBR Alonso SPA I have concatenated these ...
-1
votes
1answer
106 views

Redirect a directory as input to a script and output to a file

I want to use a directory name as a parameter for a pre-made script. Then the output goes into a newly made file in the home directory. It involves pipe/redirection. How do I do that? read dir $dir ...
0
votes
2answers
44 views

Using a file as an input to a script

Say I want to use the name of a file as input, and process it with a pre-made script in a certain directory. How do I do it? fileName < /folder1/scriptName is this the right format?
0
votes
1answer
35 views

Using $BASHPID in grep statement

I'm trying to exclude the PID of the subshell from the results returned by pgrep. Note that the name of the file is the same as the name passed to pgrep. Why does setting a variable equal to BASHPID ...
2
votes
2answers
137 views

redirect output of tee and grep for multiple logfiles

Redirecting output from a script STDOUT + STDERR toLogfile 1 and a grep to Logfile 2 ./run_test.sh 2>&1 | tee -a /var/log/log1.log | (grep 'START|END') > /var/log/myscripts.log How can I ...
5
votes
2answers
707 views

How to capture ordered STDOUT/STDERR and add timestamp/prefixes?

I have explored almost all available similar questions, to no avail. Let me describe the problem in detail: I run some unattended scripts and these can produce standard output and standard error ...
5
votes
1answer
83 views

Make program in a pipe to think it has tty

Test environment: $ mkdir testdir $ cd testdir $ echo | tee "file name" Now, ls will print file?name (under Ubuntu GNU bash, at least), while ls | cat will print file and name in separate lines. ...
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0answers
44 views

Create tar file which consists of directories from another tar file

I have tar file with three directories, dir1, dir2 and dir3. Is there a way to extract dir2 and dir3 directories to create new tar file on the fly, without extracting the directories in temporary ...
1
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2answers
62 views

If I use one of the exec family functions to open a child process, will pipes to parent be applied to the child?

Say I open a parent process with a master process that assigns the stdout to a file for logging. Then say I use the parent process to open a child with execvp (or any other of the exec family of ...
1
vote
2answers
249 views

Concatenate file contents AND names

I've been writing for many months. The files I create are dated files named like 2011-06-13.markdown with daily content. I've decided I want to have all the writing in one file instead but I'd like ...
1
vote
1answer
129 views

Is the data transiting through a pipe confidential?

I read the following question (Shell Script mktemp, what's the best method to create temporary named pipe?) but I'm wondering whether it is preferable to use a temporary named pipe to transfer ...
5
votes
3answers
398 views

Get PID of any command in backgrounded piped sequence of commands

If, in bash, I execute: cmd1 | cmd2 | ... | cmdi | ... | cmdn & where the cmd{1..n} may not be distinct, how do I get the PID of cmdi? Alternatively, how can I signal the cmdi process? (For ...
7
votes
2answers
937 views

Why does process substitution result in a file called /dev/fd/63 which is a pipe?

I am trying to understand named pipes in the context of this particular example. I type <(ls -l) in my terminal and get the output as, bash: /dev/fd/63: Permission denied. If I type cat <(ls ...
2
votes
2answers
90 views

Should I use piping or redirection for input to 'sort'

I want to do awk -F "," '{print $1 }' inputfile1.txt | sort -u > distinctOutput.txt Is this good performance-wise ? Or should I redirect / use a temp file since I think it is better to make sort ...
1
vote
1answer
86 views

What is happening while executing this command cd / | vi?

When I execute the command cd / | vi, it goes to the vi editor. When I type any command it does not display the command but it gets executed and the command that is executed is not shown in the ...
0
votes
1answer
201 views

Delete empty directories using 'ls' command

I want to delete empty directories without using find command find . -empty -type d -delete. like the following: if [ "$(ls -d *)" ]; then echo "Not Empty" else echo "Delete" fi How do I ...
27
votes
4answers
2k views

Why does “tail -f … | tail” fail to produce any output?

Why does the following command not produce any output? $ tail -f /etc/passwd | tail After reading about buffering, I tried the following to no avail: $ tail -f /etc/passwd | stdbuf -oL tail Note ...
2
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0answers
27 views

Close All Piped Commands if one close

I'm running at least 3 commands (with progs) using pipes. For example program1 bla bla | program2 blabla | program3 bla bla Is possible to close all programX PIDS automatically if at least one ...
1
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0answers
49 views

Verbose output in logfile and simple output on screen?

Let's say I have the following script: script.sh and i want the verbose output in a logfile and simple output on screen. Logfile should contain the csh -v script.sh output, and on the screen should ...
2
votes
1answer
59 views

How can I pipe the output of a program or function into a variable?

How can I pipe the output of a program or function into a variable? For example lets say I have this script: function foobarize () { sed \ -e "s|${foo}|${bar}|g" \ $1 } echo foo | ...
5
votes
2answers
200 views

How do I preserve coloured output when piping to `less -R`?

$ ffmpeg -v debug ... Coloured output. $ ffmpeg -v debug ... |& less -R Dull output. How do I make the output coloured while piping it to something?
4
votes
2answers
100 views

Problem with read variable from AWK

I'm trying to get memory info by this command: #!/bin/bash set -x cat /proc/meminfo | grep "MemFree" | tail -n 1 | awk '{ print $2 $4 }' | read numA numB echo $numA I'm getting this + awk '{ print ...
2
votes
1answer
147 views

Why doesn't PIPESTATUS work on pipelines within a command substitution

Proof below: Bash 4 Prompt> $(echo hello|sed 's/h/m/'|xargs -I{} ls {} 2>/dev/null|sed 's/ /_/') Prompt> for i in ${PIPESTATUS[@]}; do echo $i;done Output> 0 Prompt> echo hello|sed ...
3
votes
4answers
218 views

Redirect and pipe output

rpm -qa > file | wc -l returns 0. What am I doing wrong? I think it is clear what my goal is, but it isn't working. Is this a job for xargs or tee?
1
vote
3answers
369 views

How can I pipe data over network or serial to the display of another linux machine?

I have a second monitor that I'd like to use for a text-based debugging log and/or console. I don't want to have it as part of my GUI / "desktop" / main system. I have this display connected to an ...
1
vote
1answer
93 views

Why doesn't this piped script work?

#!/bin/bash rm out mkfifo out nc -l 8080 < out | while read line do echo hello > out echo $line done If I browse to the IP of the machine this script is running on (using port ...
4
votes
1answer
99 views

unexpected output with grep

I am using pyrit. For those who dont know, pyrit allows among other things to check if a wpa handshake key is valid: pyrit -r file0.cap analyze when a file does not contain a valid key, here is ...
1
vote
1answer
162 views

Why are these values not appending correctly when appended to the pipeline? [duplicate]

I have a bash script (seen here) that I'm using to sort a list of files in subdirectories by filename. This script appends sorted files in hooks/pre-relevant/, then files named hooks/pre-relevant, ...
2
votes
1answer
75 views

Is there a system call to bind a file descriptor directly into another?

A read() & write() loop would probably be as good as what I'm looking for, but nevertheless is anything like that around or is it impossible because of an obstacle I didn't envisage ? I'm curious
6
votes
2answers
481 views

check md5sum from pipe

I am confused how md5sum --check is supposed to work: $ man md5sum -c, --check read MD5 sums from the FILEs and check them I have a file, I can pipe it to md5sum: $ cat file | md5sum ...
1
vote
1answer
52 views

What standard shell command can evaluate escaped Unicode in a stream?

I'm looking for a pipeable command that will convert substrings in the form of ‘\unnnn’ to the actual characters. For example: $ echo 'co\u00ebfficient' | what_command coëfficient
9
votes
1answer
2k views

How pipes work in Linux

I've been reading up about how pipes are implemented in the Linux kernel and wanted to validate my understanding. If I'm incorrect, the answer with the correct explanation will be selected. Linux ...
1
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0answers
16 views

Test execution output of a command before a pipe [duplicate]

I would like to test the execution of a php script that redirect its stdout and stderr to a file with tee. php /path/to/script --param 2>&1 | tee -a /path/to/log if ( test $? -ne 0 ); then ...
4
votes
1answer
86 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
138 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 ...
4
votes
6answers
716 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
143 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
54 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 ...
4
votes
2answers
437 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 ...
1
vote
2answers
249 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 ...
8
votes
3answers
2k 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
39 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 ...
15
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 ...
2
votes
2answers
3k 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
295 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
127 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? ...
1
vote
2answers
4k views

How do I sort using the grep and sort commands?

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, then redirect the output of this ...
4
votes
3answers
558 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
531 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
496 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 ...