stdout is the name of the default output file descriptor of a process. Since there is nothing special about `stdout`, you *should not* use this tag. Use [tag:io-redirection] for questions on how to redirect output, use [tag:file-descriptors] for questions on how to manage file descriptors, use ...

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2
votes
1answer
33 views

non-blocking/multi-threaded cat

cat is blocking from what I see in the code, i.e. it uses blocking read() and then it uses blocking write(). I want to call some tool where I disable all stdout buffering by purpose (e.g. like ...
3
votes
2answers
18 views

stdbuf supposed behavior for subprocesses

I didn't exactly find something about the following in the man-page. How is the supposed behavior in subprocesses spawned by a process which was itself spawned by stdbuf? E.g.: stdbuf -oL myprog ...
0
votes
1answer
18 views

How do I output stderr/stdout of my script to both a file and the console?

I'm using Amazon Linux and writing a script in bash. I want to output both stderr / stdout (preferably in the order that they occur) to a file as well as the console. However, this command isn't ...
2
votes
1answer
19 views

Unable to redirect stdout/stderr to log file [duplicate]

I have a script tmp.sh #!/bin/bash echo hello sleep 3 echo 3 I want to log the script running time (as well as script stdout) to a log file. user$ time ./tmp.sh >& log.tmp real ...
3
votes
2answers
35 views

What are the default stdin and stdout of a child process?

I would like to know what are the default stdin and stdout of a child process (if there are such defaults). Are stdin and stdout of a child process the same as its parent process? Is this something ...
1
vote
1answer
21 views

Save number of lines output to a variable in a shell script without consuming the output

I have a shell script where I have a if statement based off of the number output lines output from another call. (In my case do something there is more that 1 line of output). LINES=$(function_call | ...
1
vote
2answers
9 views

redirect the output of {time}

I am trying to benchmark a single request agains a webserver, and am having a problem doing so, specifically, I am having an issue redirecting the output of the time command. If i simply run time ...
0
votes
2answers
38 views

Will the stdout output of a background process be taken as the stdin input of the foreground process?

When a background process outputs to stdout to appear on terminal, will the output be taken as stdin input to the foreground process? Note that the background and foreground process are not related by ...
0
votes
1answer
18 views

Check if stdout is attached to a terminal from an AWK script

Is there any way I can check if an AWK script's stdout is attached to a terminal, just like test -t 1 in a shell?
0
votes
2answers
26 views

Redirect stdout to file with nohup doesn't work

I'm trying to run a C-program in the background. I also want to save the stdout-outputs of the program. But if I try the following, nohup only redirects stderr-outputs to the logfile.txt: nohup ...
2
votes
2answers
47 views

How to store the printout of the last command in a shell variable in urxvt/zsh?

I'd like to have the printout (stdout and stderr) of the last command run within zsh available in a variable ready to use grep, etc on it.
1
vote
2answers
28 views

I want to catch the STDERR and STDOUT of Background running script

I have to run a script background and also i have to catch the STDERR and STDOUT . i'm using the below line . test.sh & >> log_file 2>&1 But un fortunately nothing is getting ...
16
votes
5answers
792 views

How to trick a command into thinking its output is going to a terminal

Given a command that changes its behaviour when its output is going to a terminal (e.g. produce coloured output), how can that output be redirected in a pipeline while preserving the changed ...
3
votes
3answers
96 views

Direct output to pipe and stdout

I was wondering if there is a way to pipe the output of a command and direct it to the stdout. So for example, fortune prints a fortune cookie and also copies it to the clipboard: $ fortune | tee ...
0
votes
0answers
17 views

Where is the logging of an application launched from the GUI buffered before being sent to a log file?

This is a fairly difficult question for me to word, but I'll try my best. When I launch an application from the terminal, say, Banshee as an example (so banshee to launch from terminal), I can see ...
1
vote
1answer
27 views

`docker logs foo | less` isn't searchable or scrollable but `docker logs foo 2>&1 | less` is

Using either one gives readable text. But only with the stderr redirect can one scroll or type /somepattern and get matches. Without it searching gives "Nothing to search (press RETURN)" and a ...
5
votes
6answers
8k views

How to add new lines when using echo

Why the following command does not inserts new lines in the generated file and what's the solution? $echo "Line 1\r\nLine2" >> readme.txt $ cat readme.txt Line 1\r\nLine2
39
votes
9answers
11k views

How to do nothing forever in an elegant way?

I have a program which produces useful information on stdout but also reads from stdin. I want to redirect its standard output to a file without providing anything on standard input. So far, so good: ...
1
vote
2answers
152 views

Read from and write to file from stdin and stdout

I need to continually read from and write to a (virtual) file in bash, without closing the file in between. I'm looking for a program which will open the file for read and write, read from stdin and ...
1
vote
1answer
22 views

Prevent script from generating stdout if called from given program

I want my gnome-terminal to show my current user and host in its titlebar, and that of the remote when I am using ssh. To do that, I created a script ~/bin/ssh, with ~/bin in my PATH before /usr/bin: ...
12
votes
4answers
11k views

bash: Use a variable to store stderr|stdout redirection

Is there any way to redirect stdout and stderr via variable like adding command options in script? For example I have a script: #!/bin/bash -x TEST=">/dev/null 2>&1" OPT='-p -v' mkdir $OPT ...
4
votes
3answers
188 views

Trying to make sense of bash redirection syntaxes and their outputs

I'm new to Linux and trying to understand how redirections work. I have been testing various syntaxes for redirecting stdout and stderr to the same file, which don't all produce the same results. ...
3
votes
2answers
37 views

vim: Force specific syntax via command-line argument

When I want to easily read my PostgreSQL schema, I dump it to stderr and redirect it to vim: pg_dump -h localhost -U postgres dog_food --schema-only | vim - This gives: vim does not have a ...
1
vote
2answers
61 views

shell stderr to /dev/null

I have PID file and I want to get PID number so this is what I am doing. [root@linux ~]# PID=`cat /usr/local/foo/var/run/foo.pid` [root@linux ~]# echo $PID 3414 sometimes this file doesn't ...
0
votes
1answer
38 views

Create a two line text file without anything written to stdout

So basically I want to write a two line file containing this: This is line one This is line two I can easily do this by doing this command in bash: echo "This is line one\nThis is line two" > ...
1
vote
0answers
14 views

Suppress warning of rbenv versions if no rubies installed

At the moment I'm working on Ansible role that installs ruby with rbenv. In order not to install same ruby version every time I run setup task I have to check that no needed ruby is already installed. ...
0
votes
4answers
85 views

How to log from inside the script along with stdout

I am aware that I can log using tee But I want to log from inside my script, at the same time display the content on the stdout. Example, my code looks something like this: names=$(print("name1 ...
6
votes
5answers
2k views

How do I break up a file like split to stdout for piping to a command?

I have a large .sql file full of SELECT statements that contain data I want to insert into my SQL Server database. I'm looking for how I could basically take the file's contents, 100 lines at a time, ...
9
votes
2answers
10k views

Execute command in remote active terminal

Suppose you have a terminal emulator (T1) open with a PID of 6350. From another terminal, type this command (C1): echo "ls\n" > /proc/6350/fd/0 This writes ls and the new line in T1 but does ...
2
votes
2answers
71 views

Output is in console but not part of stdout or stderr

I have a command that outputs the following: READY Listening.... HELLO READY Listening.... TEST It is speech recognition from pocketsphinx_continuous. I need that output redirected to a file, and ...
3
votes
5answers
200 views

Concatenate contents from stdout and from file

How can we concatenate results from stdout (or stderr) and a file into a final file. For example ls -a | grep text1 concatenate with file2.txt into a final result (not file2.txt), without storing ...
2
votes
3answers
35 views

What is regarded as “ideal” in relation to using stdout/stderr for output in different situations?

I have seen stdout and stderr used in a variety of different ways - as far as I understand, it is common to use stdout for general information and stderr for errors and the like. However, I have also ...
19
votes
3answers
1k views

Is it safe to type another command into STDIN while the previous command is writing to STDOUT?

Perhaps this has been answered previously, I would welcome a link to another answer... If I execute a shell command (in a bash shell) like the following: make Then while the output from make is ...
0
votes
4answers
175 views

How to display output of command while also parsing it?

I have two commands, build and deploy. Currently I run build manually, parse its output using my own eyes, and use a value I find in the output as an argument to deploy. The process looks something ...
1
vote
1answer
97 views

vimdiff to compare output instead of files

I am trying to compare two command output (no files) vimdiff "$(tail /tmp/cachain.pem)" "$(tail /etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem)" I tried playing with redirection, pipe, and vim - ...
5
votes
4answers
2k views

Reuse last line of output from shell command

I am compiling something and depending on success (last line of output contains "success"= I want to scp the binary to the target. I'd prefer a piped oneliner. Is there a way to do this?
0
votes
0answers
19 views

Piped sequence - printing

I need to write a piped sequence of commands that prints out a list of all sub directories of a current directory. In order to get all sub directories of a current directory I use: ls -D Since I am ...
0
votes
2answers
155 views

how to redirect output of ssh to a file

I want to make ssh connection to my server but I don't want to enter password. I want to save output to a file like so: $ ssh root@x.x.x.x -p 22 1>output 2>&1 but when I run it the output ...
0
votes
0answers
99 views

Stop stdout log being clipped (by heroku-local)

I run heroku local with the Procfile: web: start-nginx gunicorn -c gunicorn.conf.py app:app start-nginx does some environment setup, and then ends with: { nginx --some-params & $@ ; } the ...
2
votes
2answers
783 views

pipe stdout-to-file with wc

I'm working on a lab assignment for a class, which exemplifies users | wc -w as displaying the number of users currently logged in. The instructor has asked we write the output of users to a file ...
0
votes
2answers
42 views

Unclear where bash output is going

I made a small script to output the list of vim plugin remotes to a file, so I could figure out what ones I want to keep or remove. However, when I run it, the output doesn't get piped to the file. ...
0
votes
2answers
74 views

Printing on “standard out” and “standard error”

I'm puzzled over some terminology used in my homework: So, the way I understand the question is that I should print echo, cat, etc., which I would do like with the echo command, for example echo ...
1
vote
2answers
115 views

Duplicate stdin to stdout and stderr, but in a synchronized way

I need to duplicate the stdout of a producer and feed it to two consumer in a synchronized fashion. consumer 1 producer | duplicator | consumer 2 ...
0
votes
0answers
32 views

fs_usage: a part of stdout is missing.. Where did it go?

I'm using $ fs_usage -f diskio to spy on processus when I hear my hard drive spinning for no reason, so that I know who is working so hard.. Here is one sample line: 16:14:13.785568 ...
1
vote
1answer
95 views

How to know if output is being redirected to a file? [duplicate]

I am working on displaying output like ls command (just ls, no options). And I have a working program using the system calls. But I experienced a strange behavior while testing as shown below. $ ls ...
6
votes
3answers
262 views

Are unix[-like] programs capable of determing where their output is going? [duplicate]

Up until recently I was under the impression that Unix-y programs were unaware of where their output went, be it to standard out, redirected to a file, or into a pipe. However, an unrelated U&L ...
6
votes
2answers
109 views

Notification Listener Behaving Strangely when Backgrounded

I've been struggling to get my IRC-Bouncer/Notification Script working. This is meant to be a script which will automatically login to a remote machine, attach to a screen session (or start one if ...
1
vote
4answers
1k views

Inserting the command line text before output in stdout (for pipe / redirection)

Consider the following bash constructs: ls /usr/include/asm > list-redir.txt ls /usr/include/asm | tee list-tee.txt In this case, list-redir.txt and list-tee.txt will be identical, and will ...
1
vote
3answers
164 views

in bash script; a process stdout as filename argument fails when you open it more than one time

Consider this bash script code: #!/bin/bash function bug_part() { cat $1 > sample.first cat $1 > sample.second #second time you open file $1, it contains no data } bug_part <(echo ...
1
vote
1answer
162 views

Prevent ssh-keyscan from generating output

Problem: When running ssh-keyscan in cron it emails me the output of ssh-keyscan every day. The email simply contains the following. # <hostname> SSH-2.0-OpenSSH_5.3 My (simplified) cron ...