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

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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) ...
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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 ...
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51 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 ...
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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
19 views

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
30 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. ...
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26 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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51 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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40 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 ...
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1answer
83 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 ...
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1answer
37 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. ...
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3answers
55 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 ...
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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
55 views

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 ...
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1answer
18 views

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 ...
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2answers
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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 ...
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5answers
745 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 ...
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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 ...
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1answer
32 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 ...
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2answers
34 views

How can I copy the output of a command in the terminal to my clipboard? [duplicate]

I have a script that operates on enormous files and outputs an enormous amount of content (almost 7000 lines). I need to copy the output of this to my clipboard so I can then paste it into paste2.org ...
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Understanding i/o redirection in the context of _process substitution_

Running GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu). I don't really understand process substitution (ProcSub) from the perspective of a user interested in lifting the hood on i/o ...
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1answer
41 views

Some errors are not logged, after redirecting both stderr and stdout to a file

In a Linux server, I run a program and log its stdout and stderr outputs to a file by: myprogram.py > logfile 2>&1 All the outputs to stdout and stderr are logged, except that some errors ...
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2answers
48 views

Understanding redirected if-statement in bash

if [ -z "$OPTION" ] # if option is not given(empty) then: then command1 --defaultOption else command1 $OPTION fi \ 2> >( function1 "$DETAILS" ) \ < <( command2 ...
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echo $variable > file in a loop outputs only the last value of variable

Here's what I'm trying to do: I have several git repos. I want to setup a push-to-deploy script for each of them. being so lazy to do that for each and every repo, I wanted to script it. My script ...
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1answer
15 views

GDB - Call second program

I have a program which I want to debug gdb. And I want to call a second program to redirect the output to the first program. How this is done in gdb. I tried it like that: run -2 < $(python ...
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88 views

is linux redirect “>>” slower with bigger files?

I have a shell script which makes some analysis and prepares (i.e.: writes) some commands to run in a separated file. So I have something like that: echo my_command_to_run >> ...
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1answer
39 views

Bash : ambiguous redirect

I am trying to collect dump of java process with jstack and I have tried below command. But its saying ambiguous redirect as I cant redirect to a command. jstack -l `pgrep java` > ...
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1answer
29 views

Find files and send to a temp file

Vim does support a nice option to accept a file with list of files that are then opened in a Quickfix list. Rough example, I find all files in ~ that are smaller than 1KB and pass this to Vim: find ~ ...
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7answers
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Is it a UUOC (useless use of cat) to redirect one file to another?

If I want to make the contents of file2 match the contents of file1, I could obviously just run cp file1 file2. However, if I want to preserve everything about file2 except the contents—owner, ...
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1answer
43 views

Run git command to save output but consume STDERR too

I've tried: status=$(git status -s ./$name>&1) status=$(git status -s ./$name >2 /dev/null >&1) status=$(git status -s ./$name >2 /dev/null) status=$(git status -s ./$name > ...
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20 views

How to redirect output of cowsay to be the input of zwrite

I run cowsay, which asks me to input text string. Then, it prints the result to stdout. I want to redirect that result to zwrite instead of stdout. The issue is that I can't do cowsay | zwrite ...
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Do redirections operate on file descriptors or file handles?

From https://www.gnu.org/s/bash/manual/html_node/Redirections.html Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. ...
3
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1answer
55 views

Duplication of file descriptors in redirection

From https://www.gnu.org/software/bash/manual/html_node/Redirections.html Bash handles several filenames specially when they are used in redirections, as described in the following table: ...
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1answer
39 views

Starting job via SSH and detaching from a composite command

I'd like to start a long running script via SSH and immediately return. Afterwards, I want to check the remote host every 5 minutes to see if the job is done. In order to accomplish the first part, I ...
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1answer
52 views

How to read from stdin in process substitution? [duplicate]

I would like to send stdout to multiple commands, however I'm not sure how do I read from standard input within process substitution? My attempts: $ echo foo >(cat /dev/stdin) >(cat ...
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1answer
34 views

Why cron not outputting to file? [duplicate]

I scheduled a cron task: 0 */10 * * * aapa bash /home/aapa/scripts/es_backup.sh &>> /var/log/super/es_backup.log It is running as logged into syslog: Dec 4 08:17:01 dexter CRON[15552]: ...
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3answers
145 views

What do the `echo $?` and `ls >> $File 2>&1` commands do?

Can someone help me with understanding this. echo $? -- I know it outputs a variable of some kind... and this ls >> $File 2>&1 ---- can someone explain what this does?
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1answer
55 views

Need Explanation For Multiple Arguments And Input Redirection With Cat

Files along with their contents:- ~$cat a aaa aaa aaa ~$cat b bbb bbb bbb ~$cat c ccc ccc ccc Commands that I need explanation:- ~$cat 0< a aaa aaa aaa ~$cat 0< a b bbb bbb bbb ~$cat 0< a ...
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1answer
56 views

Process substitution and cat: can't read stdin

The process substitution <(cat) doesn't work. Why? head <(cat) cat: -: Input/output error I can use an extra file descriptor, but I don't understand why the above doesn't work. # Using file ...
0
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1answer
57 views

Cron to find exec cp and redirect output with time / date per line?

I try to setup a cron task to run a set of basic shell commands. I need to look to any files created on the last day, then copy to another folder and generate a log stating, line by line, the date ...
0
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1answer
118 views

How to resolve this “ambiguous redirect”

I have a script with a function in it: function install_log() { echo "$1" >> $INSTALL_LOG_OUTPUT 2>&1 } This function is working as it should. It is a function to write something ...
0
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0answers
28 views

Redirecting output of a pipe to a file [duplicate]

I'm executing the following command blkcat /dev/sdg3 0 724566015 | grep -n 'USE `.*`;' that produces output on screen. If I type that command: blkcat /dev/sdg3 0 724566015 | grep -n 'USE `.*`;' ...
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run command line contains redirection >> inside Guest VM

Another alternative of running ls -l /home for example in Guest VM called myvm ,is to run on the host the following command : vboxmanage --nologo guestcontrol myvm --username root --password xxxx ...
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2answers
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For input redirection, are there functional differences between bash/zsh <<<“$(<file)” and the traditional <file?

I'm asking only about the usage which would have the similar effect as traditional input redirection from a file. <<<"$(<file)" as far as I can tell is equivalent to <file It ...
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Why process does not (seem to) exist before fifo read

I have a trivial Python script: #!/usr/bin/python import os, sys sys.stderr.write('I am %s' % os.getpid()) sys.stderr.flush() print "hello" sys.stderr.write('I am done') When I run this script ...
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81 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 ...
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519 views

How to redirect the output of a command to an already existing file without deleting its contents? [duplicate]

I am making a backup of some files and am creating a checksum file, checksums.txt, to later check the integrity of my data. However pasting each checksum manually into the file is inconvenient since ...
3
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2answers
54 views

can not access standard output from a command

I'm using this command format: cmd0 > >(cmd1) 2> >(cmd2) Cmd2 needs to echo data back to zenity as it processes some data, but zenity never hears the echos. It seems the echos are lost ...
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2answers
51 views

redirecting script variable to log file without losing stderr

When setting "set -x" inside bash script, or if you run your script with bash -x, you will get all the arguments printed to the screen together with the stdout. Is it possible to have stderr and ...
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1answer
55 views

Redirect all output with prompt to a file

What is the shortest way to redirect: $PROMPT, last executed command, stdout and stderr into single file? Of course, we might use &> to redirect stdout and stderr into single file and then add ...