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

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4
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1answer
329 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 ...
1
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1answer
2k 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
89 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
votes
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 ...
1
vote
1answer
143 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
149 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
103 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 ...
1
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4answers
68 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
130 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
votes
1answer
153 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
votes
3answers
785 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 ...
1
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1answer
222 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
249 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
vote
1answer
749 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
68 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
875 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
419 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
231 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
2k 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
83 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
354 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
97 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
votes
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 ...
27
votes
5answers
22k 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
140 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
104 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 > ...
12
votes
3answers
3k 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
97 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 ...
9
votes
3answers
671 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
votes
2answers
245 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 ...
5
votes
1answer
10k 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
votes
2answers
319 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 ...
4
votes
1answer
649 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
185 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
2k 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
174 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
255 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
votes
4answers
253 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
800 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
439 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
199 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
votes
2answers
603 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. ...
21
votes
4answers
33k 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 ...
13
votes
2answers
632 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
9k 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
387 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
323 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
155 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 ...