io redirection is the process of changing where the output and input of a program originate

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2
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29 views

Connect via telnet and doing certain operations

I'm trying to code a script where I can connect via telnet to another server and execute certain operations, but I'm having problems with the result of this process. The objective is to connect to a ...
0
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0answers
23 views

Emptying a log file getting updated with 2>&1 output redirection [duplicate]

I have a server which constantly writes outputs and errors to stdout and stderr. The command line I use for running my server is: Server options-list > log.txt 2>&1 & Now the problem ...
0
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2answers
63 views

Piping sed/grep output does not work

If I run the commands bellow, only out1 has output, the out2 and out3 are empty. # this is just to generate a self-signed certificate openssl genrsa -out /tmp/ssl.key 2048 openssl req -sha256 -new -...
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2answers
166 views

How to redirect STDIN of background process?

In my Ubuntu, i run java application in background. I use bash script to run it and now it looks like: nohup java -jar app.jar & exit 0 The problem that i want to be able to write an input ...
10
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1answer
816 views

Shell variable $_ not behaving as expected

What the reason the number of lines differs? $ head -n 100000 ./access.log > ./data/log.sample $ cat $_ | wc -l 1933424
0
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1answer
22 views

Archlinux'es pacman + tee == unclear console IO [closed]

I have a small issue with capturing the pacman's IO with the tee utility. I try this command line: pacman -S group-1 group-2 | tee pacman.log And there is an issue: when the pacman query which ...
1
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1answer
41 views

“time > time.txt” refuses to work propely

I just started learning Linux commands. I was experimenting with the > command, that, as far as I understand, makes the command before it write it's output to the file after the sign. This ...
0
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1answer
31 views

Redirection Error in Function [closed]

I'm trying to figure out why the code below doesn't work, and gives me an error Bad file descriptor. It is sort of a follow-up to this question as applies to the script I'm currently working on. ...
3
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2answers
88 views

Returning a String and Understanding Redirection and Output

I'm trying to figure out how redirects could be used to selectively output a string from a bash function which needs to print multiple lines to the terminal. I found an answer on this question at ...
1
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2answers
52 views

Difference between 1> and >

Is there any difference between (# comments taken from documentation) command > filename # Docs: Redirect stdout to a file. and command 1> filename # Docs: Redirect stdout to file "filename....
2
votes
1answer
33 views

Sending `time` command into text file [duplicate]

I want to get the result of time command into a text file but it's not working it only put blank space in the text file. I already tried this commands, A- $ x=`time` $ echo $x > log.txt $ cat ...
4
votes
1answer
93 views

File descriptors and redirect in bash

Can someone explain why this command works: gpg --enable-special-filenames --verify --batch \ <(curl -s https://www.gnupg.org/ftp/gcrypt/gnupg/gnupg-2.0.29.tar.bz2.sig) \ <(curl https://www....
4
votes
3answers
195 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. ...
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2answers
64 views

How can I clear/empty a file being piped to?

Say I have some process which pipes to a file: yes > foo I know want to clear/empty the file foo, but still want the process to write to the file, i.e. start filling the file again after ...
0
votes
1answer
116 views

avahi-daemon fails to start with “Failed to chroot(): Permission denied”. But only without stderr-IO-redirection

After a recent upgrate, avahi-daemon is not starting up anymore. Furthermore, the behaviour differes weather if I redirect stderr to a file or not. If I start avahi-daemon --debug with debugging ...
2
votes
1answer
55 views

redirect to a named pipe

I know the difference between > and >> when redirecting to a plain file. But is there a difference when redirecting to a named pipe (fifo)? Assume the namedpipe is a named pipe. Are the ...
3
votes
3answers
64 views

redirecting output of a command as if it was file input

I find myself always having to arrow up and going backwards through the command line to change one part of an earlier command that is pipped to a later grep or head or whatever command. For a crude ...
2
votes
1answer
33 views

Possible redirection bug in zsh 5x

[This post's title needs some work; suggestions welcome.] The following command produces different outputs in zsh v. 4.x and 5.x: { ( printf "X\nY\n" printf "WARNING: foo\nWARNING: bar\n"...
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2answers
80 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
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2answers
205 views

Why we need to have 2>&1 in /dev/null 2>&1?

I saw in linux script there was a command argument > /dev/null 2>&1, I know it is to redirect the output to null, means silencing it. I also know about the numbering for 0,1,2 (STDIN, STDOUT,...
0
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0answers
19 views

Redirect stderr to stdout and tee to file and check return value [duplicate]

I know how to redirect stderr and stdout to a file: curl -sSo file http://foo.bar >> log 2>&1 I know how to get stdout to appear on the console and in a file: curl -sSo file http://...
0
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2answers
43 views

Output pings with time greater than 100ms to file with a timestamp appended

I want to save in a file every ping with a time greater than 100ms and append a timestamp to every line. Searching I have managed to get this: ping HOST | grep --line-buffered "time=[0-9][0-9][0-9]" ...
6
votes
3answers
695 views

Does the shell fork when I use built-in commands?

When I run the command type type, this gives me a result to standard output. So, now I try this command: type type > abc.txt It redirects the standard output to abc.txt. So, if this command ...
0
votes
1answer
41 views

using command line arguement with redirecting

#include <fcntl.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char** argv) { int val; if(argc!=2) { printf("Usage: %s <...
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2answers
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Is the delimiter in here document seen and used by the program which takes it as input?

The format of here-documents is: <<[−]word here-document delimiter Is the delimiter seen and used by the program which takes the here document as stdin input? Or is the delimiter used by the ...
3
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2answers
166 views

Order between `nohup`, `&` and redirection?

What is the correct order between nohup, & and redirection, when using together? Why are other orders not correct? For example, $ nohup firefox& &> /dev/null $ nohup firefox &&...
3
votes
1answer
170 views

Stdin input to a command with nohup

from http://www.gnu.org/software/coreutils/manual/html_node/nohup-invocation.html nohup runs the given command with hangup signals ignored, so that the command can continue running in the ...
0
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2answers
90 views

bash: tee eats newlines after exec

To output both stdout and stderr from a script to the console and to a log file, I’ve found a beautiful solution with tee: exec &> >(tee log.file) The problem is, that sometimes tee seems ...
2
votes
3answers
47 views

Script output depending on parameter

I have script that prints out few lines of text. This text is used as configuration by other process. When I normally run program I redirect standard output to file which is fine: ./generateConfig....
7
votes
1answer
354 views

How can I pipe only stderr in zsh?

In bash: $ echo hi 2>&1 1>/dev/null | cat $ While in zsh: $ echo hi 2>&1 1>/dev/null | cat hi $ Is there a way to pipe only standard error while redirecting standard out?
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1answer
39 views

trap echo does print not write to console when writing to file

When I terminate "CTRL+C" the following script #!/bin/bash function waa(){ for i in {1..10} do echo "start.sh: sleeping $i" sleep 1s done } trap "echo 'GAGA'" TERM waa >&...
2
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1answer
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Two input pipes through file descriptor shuffling and /dev/fd

I want to pipe two programs into one. If my shell supports it, I can use Process substitution. For example, to list the common lines of two files in indifferent order, I can use comm -12 <(sort a) ...
0
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2answers
365 views

Bash - Redirect output to a variable or file descriptor, then read from the variable or file descriptor

Here's an example of a bash script that redirects all output to a file (and shows output on the screen too): # writing to it exec > >(tee --ignore-interrupts ./log) exec 2>&1 echo "here ...
1
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1answer
139 views

patch: “bad file descriptor” in combination with pipe and LD_PRELOAD/ libtrash

Very short summary: cat "$file" | patch produces a Bad file descriptor-error, but patch < "$file" works, when libtrash is preloaded with LD_PRELOAD, and only on bigger projects. Description: For ...
1
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1answer
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How to get file descriptor number of a output and how to redirect all of them at once

Lets take this command for example $ time ssh ec2 ls www apps real 0m0.554s user 0m0.004s sys 0m0.000s $ time ssh ec2 ls 1>/dev/null real 0m0.554s user 0m0.004s sys 0m0.000s $...
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2answers
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Trying to direct variable contents into command gives Ambigious Redirect

I'm trying to write a script which tests the http response from various Node servers I have running and which then emails me if any respond with a 502 error from Nginx (meaning one or more server has ...
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3answers
36 views

How do I organize and cut this portion of a directory into a file?

I'm new to unix and I'm not sure how to name my title but my main objective is to copy the contents of a directory and send it to a file. Then cut out the directory location to just have the name. ...
4
votes
1answer
33 views

Prevent customized bash autocomplete from affecting io redirection (< and >)

I've used complete -W 'firstdatabase databasetwo etc' mysql to save a list of databases, so that I can autocomplete them using the mysql command. However, in many cases I would type mysql db < /...
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2answers
107 views

Unable to run a process on background

I need help with a Solaris system. I have used the following command to run the cp.sh script in the background. nohup sh cp.sh < /dev/null & > /dev/null & output: Invalid null ...
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2answers
208 views

Copy output of curl to file

I'm running raspbian and using this bash script to take a photo every minute and upload it to my FTP server: #!/bin/bash while [ 1 ]; do DATE=$(date +"%Y-%m-%d_%H_%M_%S") raspistill -q 10 -th none ...
2
votes
1answer
98 views

What kind of redirection is >>&?

I'm looking at a cron file that has the following line: 35 0 * * * /bin/csh -c "/home/abc/.cshrc;/home/abc/appTools/bin/xxx.pl >>& /home/abc/appTools/log/xxx.cronlog" Is this another ...
3
votes
1answer
41 views

How do I turn off redirection once I've turned it on? [duplicate]

I found a great solution at Redirect all subsequent commands' stderr using exec. I used the example: exec > >(tee $somelog) 2>&1 ...and managed to get everything to tee great. Now,...
1
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3answers
248 views

How to exclude the output file from ls output

Let's say I have these files on desktop: aaa.jpg bbb.jpg I want to list these two jpg's and output them to a .txt file: #!/bin/bash cd ~/Desktop ls -1 > all.txt With this code the all....
2
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2answers
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exclude target redirection file from being processed in for loop

This will cause LIST to grow very large (even a couple of GB in a short time etc): $ for i in *; do echo $i; cut -d ' ' -f1 $i ; done > LIST For example, after 10 seconds: $ wc -l LIST ...
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3answers
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Can I redirect the output of a program to cat with a pipe?

I have a folder with three files and basic contents: $ tail * ==> file1 <== file 1 contents ==> file2 <== file 2 contents ==> file3 <== file 3 contents I would like to see the ...
0
votes
1answer
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TCSH: I want to display command output and redirect to a file

I looked at the TSCH man page, which said "Either output-file or error-file may be '/dev/tty' to send output to the terminal." So if I can redirect to two different locations, that would work. But ...
3
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2answers
63 views

How to write a “compose” function of bash pipelines with named pipes

This page details psuedocode for creating a compose function that takes n commands and executes them in a pipeline: We program a command compose such that compose cmd1 cmd2 ... cmdn behaves ...
16
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5answers
821 views

Write output of `time` in a file, why are parentheses needed?

time writes to stderr, so one would assume that adding 2>&1 to the command line should route its output to stdout. But this does not work: test@debian:~$ cat file one two three four test@...
7
votes
2answers
416 views

Redirecting standard error output to bash variable

Here's a C code snippet that will cause segfault: // segfault.c #include <string.h> int main() { memset((char *)0x0, 1, 100); return 1; } Compile it with: gcc segfault.c -o ...
3
votes
1answer
67 views

Opening more than 10 file descriptors with ksh

The shell syntax for opening a file for writing and using its file descriptor is: exec 3>output.log With bash and zsh you also can write: exec 13>output.log Thus, later in your script you ...