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

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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
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1answer
205 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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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
181 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
267 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
257 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
859 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
479 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
205 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 ...
16
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2answers
617 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. ...
22
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4answers
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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 ...
13
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2answers
637 views

What does redirection with >| do?

When should you use >| for redirecting output to a file instead of just >? The explanation given when I was shown this was that it guaranteed the target file was truncated first. But I thought ...
4
votes
1answer
10k 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
460 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
1k 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
329 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 ...
3
votes
3answers
165 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
44 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? ...
3
votes
2answers
834 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
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1answer
158 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
54 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
703 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
410 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 ...
7
votes
3answers
282 views

How to run a command while logging output to a file?

I have a console application that needs to be run as part of the deployment of a new application version on my server. This console application is designed to output to the console, and cannot be ...
5
votes
1answer
123 views

Replacing stdout with stderr

Is it possible to redirect the output from a command to replace the text sent to stdout with the text from stderr? $ ./script this line is redirected to stdout this line is redirected to stderr $ ...
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votes
3answers
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Restoring output to the terminal after having issued “exec &>filename”

I am trying to execute the following: exec &>filename After this I am not able to see anything including what I typed, alright. I frantically try , exec 1>&1 and exec 2>&2 , ...
0
votes
1answer
42 views

Output redirect complexities

I'm trying to have a script exit with an error in the event it can't reach an X server: xset -q &> /dev/null || { echo "The Display Server is BROKEN. Aborting."; exit 1; } However, I'm getting ...
16
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2answers
474 views

Why does this command create an enormously large file?

I was experimenting today with some append operations and, in my curiosity, ran this (where file1.txt was non-empty and file2.txt was empty): $ cat file1.txt >> file2.txt >> file1.txt ...
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2answers
718 views

What stream does perf use?

What stream does the perf command use!? I've been trying to capture it with (perf stat -x, -ecache-misses ./a.out>/dev/null) 2> results following http://stackoverflow.com/q/13232889/50305, ...
5
votes
1answer
124 views

Is it possible to create sticky redirection from stdout/stderr

Consider such code: echo hello >> log.txt echo world >> log.txt I execute command with stdout redirection. Is it possible to create sticky redirection? Something like this: redir ...
2
votes
1answer
133 views

Redirecting an active port

Environment: Web server that requests pages on a specific port from an application server. Problem: If a page request comes into the application server during the restart of a certain web application ...
3
votes
1answer
211 views

Pipeline and redirection understanding

Please explain this script (from ABSG. Ch. 20): exec 3>&1 # Save current "value" of stdout. ls -l 2>&1 >&3 3>&- | grep bad 3>&- # ...
13
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4answers
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Is it possible for a sysadmin to eavesdrop on his/her users' terminals?

When logged in to a machine, I can find out each user's pseudo-terminal device(s) from the output of w. Being a sysadmin, is it possible for me to eavesdrop on this terminal without the user being ...
4
votes
2answers
1k views

What does “sh a.sh <&0 >&0” mean?

It's a question about bash shell command. "sh a.sh <&0 >&0" What dose it mean? Especially, I'm not very clear about what does &0 mean?
2
votes
1answer
179 views

xargs and < and > to the same files

I want to run git stripspace on all my source code files, on each build (or precommit or just manually), to remove extraneous whitespace, and later maybe to format the code in a standard way, So ...
10
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Is this a typo in Bash manual's redirection section?

Note that the order of redirections is significant. For example, the command ls > dirlist 2>&1 directs both standard output and standard error to the file dirlist, while ...
3
votes
2answers
128 views

Is it possible to create a “file” that can be used by any process without actually saving the file on disk?

Suppose I do a grep that gives me a lot of results. I want to use the output of grep and pass it to a command that takes a filename as it's first argument. For example - myCommand filename.txt I ...
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votes
3answers
1k views

Pipe command output to input of running/backgrounded command

In Bash 4.X It it possible to do something like: command that expects input & echo some output | %1 Where %1 represents the first backgrounded command?
0
votes
1answer
70 views

Resume input from user after file is read [duplicate]

I have a program that reads user input—moves, it's a boardgame—from the user. Like so: $ game enter your move: # etcetera The first N moves I need to repeat each time, so I put them in a text ...
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vote
3answers
667 views

How to capture the standard output of a script that depends on the user for some input?

There is a script that requires me to enter the password before it continues: bash-3.2$ ./script.sh <parameter_list> Enter the password for the Database: .. .. I am interested in capturing ...
4
votes
3answers
2k views

How to stop redirection in bash

I use : exec >script.log 2>&1 in my script to redirect all output to a file. At the end of the script I would like to print a message to the screen. How do I stop the redirection?
9
votes
1answer
9k views

Redirect both stderr and stdout to /dev/null with /bin/sh

Tried all sorts of ways to redirect both stdout and stderr to /dev/null without any success. I have almost my entire life run bash which i've never had this issue with but for once in BSD i'm stuck ...
3
votes
2answers
123 views

Diverting a file write to process

I have an OSX GUI application which I can't change - it writes new CVS lines to a log file when it completes a job. I'd like to work with these new lines, but they are constantly being added. Is ...
0
votes
1answer
310 views

no stderr output when using stdbuf -o 0 |& tee log

I want to log the standard output and error info from running my program, using the following command: stdbuf -o 0 ./myprogram|& tee mylog it works fine in one computer, I can see both ...
11
votes
1answer
14k views

How to redirect stdout and stderr to a file and display stderr to console?

I know how to redirect to a file, and use tee; on a basic level. So $ alias outanderr='bash -c "echo stdout >&1; echo stderr >&2"' # A fake "application" displaying both output and ...
12
votes
3answers
469 views

When to use redirection to stderr in shell scripts

I know that well-behaved utilities like grep output "normal" messages to stdout, and error messages to stderr. $ grep '^foo' file1 file2 file1:foo grep: file2: No such file or directory When I'm ...
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2answers
229 views

Do redirection operators always open file descriptors in parallel?

1. Consider snippet#1: $ cat test.txt > test.txt cat: test.txt: input file is output file It seems that cat makes its input file descriptor point to test.txt and then when it tries to set its ...
2
votes
3answers
756 views

How to use arguments with 'find -exec'? [duplicate]

I'm trying to generate static html files for all php scripts inside dir: find . -name "*.php" -exec php {} > {}.html \; But it just dumps all results to {}.html. How to do it properly? And how ...
20
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3answers
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How to append multiple lines to a file with bash

I am writing a bash script to look for a file if it doesn't exist then create it and append this to it: Host localhost ForwardAgent yes So "line then new line 'tab' then text" I think its a ...
3
votes
1answer
355 views

Running time command with cron

So I have a crontab that have this line: 30 16 * * * (time sysbench --test=cpu --cpu-max-prime=20000 run) 2>> ~/cpu.out I use this because time output goes by default to stderr and I want to ...