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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1answer
68 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
35 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
74 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 ...
4
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1answer
103 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
523 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
114 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
119 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 ...
1
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1answer
165 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
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2answers
255 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
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2answers
47 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
votes
4answers
224 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
105 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
138 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
1answer
321 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
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1answer
70 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
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2answers
63 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 ...
1
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1answer
47 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 ...
3
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2answers
312 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 ...
19
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5answers
6k 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
94 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
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1answer
72 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 > ...
5
votes
3answers
564 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"' >> ...
3
votes
3answers
73 views

capture output from command without interference

How can I test whether a command's output is an empty string without interfering with said output? Example: command | ??? if [ $? = 0 ] && [ -n "$output_from_command"]; then ... I'd ...
8
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3answers
383 views

Why does the less-than sign not work as a replacement for cat in bash?

I heard about "useless use of cat" and found some suggestions, but the following outputs nothing in my bash shell. < filename Using cat works as expected though. cat filename I'm using Fedora ...
11
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2answers
193 views

Output order with process substitution

This is what I usually do to run grep and wc on a file without having to scan it twice <file.txt tee >(grep LITERAL) >(wc -l) >/dev/null However, this yields EXEC LITERAL 32 ...
2
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1answer
3k views

nohup: ignoring input and redirecting stderr to stdout

I am starting my application in the background using nohup as mentioned below - root@phx5qa01c:/bezook# nohup java -jar ./exhibitor-1.5.1/lib/exhibitor-1.5.1-jar-with-dependencies.jar -c file ...
3
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2answers
195 views

Bash if script is called from terminal echo stdout to terminal, if from cron do not echo output

I would like to have a service watchdog script echo the status to the screen if called like ./watchdog.sh but if it is run by cron, there is no need to echo output. What is the proper method? Where ...
3
votes
1answer
207 views

ProxyCommand without socat, nc or Bash's TCP redirection?

ssh_config's ProxyCommand allows to establish some connection to a proxy prior to establishing the connection to the actual target machine. Simple question: how can I leverage the dynamic or SOCKS ...
0
votes
1answer
69 views

&> redirection not working correctly

Please see the following shell transcript: $ ls input.txt test-amp-gt.sh test-both-2.sh test-both.sh test-gt.sh $ cat input.txt input file $ cat test-gt.sh #! /bin/sh cat input.txt > ...
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3answers
643 views

Line 4: $data: ambiguous redirect when using passwordbox

I want to create a passwordbox using the dialog package. #!/bin/bash data=$(tempfile 2>/dev/null) trap "rm -f $data" 0 1 2 5 15 dialog --title "Password" \ --clear \ --passwordbox "Enter your ...
0
votes
2answers
112 views

Caveats with Stdout/Stderr Redirection to Files?

I was thinking about having the programs that start on login output their stdout/stderr to files, so I can check the stdout/stderr for any of them if necessary. I also plan to overwrite the last log ...
2
votes
1answer
141 views

What does the expression $(<“dir/file”) mean in bash?

In a bash script I cannot post here I see the following expression: $(<"dir/file") From what I understand the expression $(...) evaluates a command inside (as when using backticks), but what is ...
10
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4answers
222 views

How to “combine” lines printed by multiple programs safely?

Suppose I want to execute multiple programs in parallel and combine their outputs to one pipe: sh -c ' (echo qqq; echo qqq2; echo qqq3)& (echo www; echo www2; echo www3)& (echo ...
7
votes
3answers
291 views

Redirect output from all commands to file, not just last

I want to add a header to a file with echo, then use a command to create the rest of the file. This means I'll be using two separate commands. How do I write the output from both commands to a file ...
2
votes
1answer
138 views

redirect error out to standard output

I can save the error out in the same file as standard out. I have used this method below. The problem is that the error out is "always" shown at the top. In the example given below the error relates ...
2
votes
2answers
155 views

turn off buffering for `hping` in OpenBSD

It would appear that the output from hping is fully buffered when piped to perl for further line-by-line processing, so piping hping to perl doesn't work. hping --icmp-ts example.ca | perl -ne 'if ...
15
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2answers
496 views

How can I stream data to a program that expects to read data from a file that is given as a argument?

I have a huge gzipped file and I want a program (4s-import in this case) to read it. It takes a lot of time to first unzip the file and then call the program with the path to the file as an argument. ...
6
votes
3answers
5k views

How do I completely silence a cronjob to /dev/null/?

On my Ubuntu-Desktop and on my debian-server I have a script which needs to be executed each minute (a script that calls the minute-tic of my space online browsergame). The problem is that on ...
12
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2answers
371 views

Redirecting using >|

Can someone explain the utility of using >| for redirecting output to a file instead of just >? When I was shown this technique the explanation was that this guaranteed the file was truncated ...
3
votes
1answer
321 views

What does 2>&1 in this command mean? [duplicate]

I understand that this command attempts to write to nowhere or a null device but what does 2>&1 mean here? wget -q -O - http://yourwebsite.com/wp-cron.php?doing_wp_cron > /dev/null ...
2
votes
2answers
156 views

How do I redirect only stderr?

I am having a bit of trouble doing this. I am required to run a compiled .java file and redirect only stderr to a file called error. So the .java file is named javaProgram.java. This is what I have ...
2
votes
1answer
598 views

How do I redirect all writes and reads from /sdcard/whatsapp/ to /sdcard/shared/ on android?

I am using bluestacks appplayer beta with a rooted android, I want to redirect all writes and reads from one directory to another, how do I do that? I have a terminal available to put commands in..
2
votes
2answers
214 views

What is the use of “&>>” in bash?

I was studying a bash script code where I encountered operator "&>>". I didn't understand its use. So, I referred to http://www.gnu.org/software/bash/manual/html_node/Redirections.html . It is ...
2
votes
3answers
107 views

How can a command have more than one output?

In this answer, at the very bottom, Gilles mentions that a command can have more than one output or input. Yes, there's cat foo bar | something, for having both foo and bar as inputs, and there's tee ...
2
votes
1answer
41 views

Inner logic of chained redirections

When I type cat some_file > new_file1 > new_file2 I got output from some_file in new_file2 and empty new_file1. What is the inner logic in it? More specifically what is the stdout of file? ...
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votes
2answers
460 views

Who is file owner if the file is created using sudo command?

I logged in using my username ravbholua: ravbholua@ravbholua-Aspire-5315:~$ echo $LOGNAME ravbholua I create file named a1: ravbholua@ravbholua-Aspire-5315:~$ echo>a1 ...
1
vote
1answer
100 views

Pipe not picking up stdout

I am running a java program from a OS X 10.8 bash terminal, and are trying to rederect the output it is producing. However, when either running this throug a pipe, or rederecting it to a file, the ...
3
votes
2answers
36 views

io redirection to “cross” 2 programs

How to "cross" stdin and stdout of two programs? Specifically, I have 2 programs call pgm1 and pgm2, they are interactive tic-tac-toe games. They both output a number (0to8) indicating position where ...
4
votes
3answers
465 views

Split stdin by lines

I want to invoke a command for every line of the standard input, much like xargs, but the line should be passed as standard input, not as a command-line argument: cat some-file.txt | <magic> | ...
2
votes
1answer
135 views

input output redirection in bash [duplicate]

In Ksh for redirecting i/o from a command away from standard output/error I do , [ where command is any command that produces output/error ] command 2>filename command 2>/dev/null or command ...