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

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13
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3answers
422 views

How to log whatever I enter in terminal to file

I am a novice just learning Fedora 13. I just wanted to know if its possible to redirect whatever I type in the terminal to a file, so that I would be able to see from the file, that a particular ...
5
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2answers
346 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 Ctrl-C ...
1
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0answers
22 views

Recording shell output for interactive commands

While looking into a shell redirection problem, I found a couple of answers that pointed me to the script command. As I understand it, script just records in- and output of the terminal, and allows me ...
4
votes
1answer
633 views

KSH styling text based menu using STDERR

Is it possible to format the STDERR in order to have a better looking menu using the select command? I have a simple select select oChoice in $(<tempMenu.menu) ; do case "$oChoice" in ...
1
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2answers
87 views

How to while read line with a pipe

I am currently trying read a csv file with BASH. The 10th [$f10] value of the csv file must be greater then 0 for a given machine class and machine ID [m_class] and [m_id] (these are user defined) . ...
2
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1answer
82 views

What are the Linux shells that allow network traffic management (sending/receiving data to/from `/dev/tcp/host/port`) via redirectors?

Following this Bash tutorial, I have succeded in obtaining the code of a web page issuing simple commands by using this method: $ exec 3<>/dev/tcp/www.google.com/80 $ echo -e "GET / ...
2
votes
1answer
52 views

Continously writing terminal output to text file

I am running a small cli python app in terminal. It loops infinitely and outputs text to the terminal. I want to output the text to a file, and I can do that with the following command python [my cli ...
15
votes
5answers
1k views

How can the standard input of one program be passed as an arg to another?

Let's say a program exists, which takes two arguments; input file and output file. What if I don't wish to save this output file to disk, but rather pass it straight to stdin of another program. Is ...
4
votes
1answer
2k views

“>/dev/null 2>&1” in `if` statement

I don't understand the below if condition. I know that /dev/null 2 > &1 is sending output to error stream (please correct me if I am wrong). But I don't get it when it is in an if condition ...
2
votes
1answer
105 views

I/O redirection shortcut doesn't work when at the end of a command line

I've been getting myself comfortable with I/O redirection. I've become aware of the &> shortcut for 2>&1. I believe it also works as >&. There may be a nuance to that of which I'm ...
0
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4answers
53 views

Excluding specifics lines from being redirected [closed]

Let's say I am executing a script like this : /a/b/c/script.sh >> abc.log This will mean that all the contents/execution of script will be re-directed to abc.log. If I want a particular line ...
0
votes
1answer
32 views

Redirect stdin for multiple shell functions [closed]

I'm surprised nobody has asked this before - maybe I'm just that dumb? How to I force this script to do what I intended? #!/bin/bash function One() { IFS='' read -r -n1 CHAR echo "One: '$CHAR'" ...
0
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0answers
17 views

writefile() to file descriptor produces output with alignment issue

The command that produces weird output: $ vim -ec 'call writefile(["line1","line2"],"/proc/self/fd/9") | qall!' 9>&1 1>/dev/null 2>&1 line1 line2 $ Same command ...
0
votes
1answer
28 views

More succinct alternative to “lsof -p $(pidof postgres| sed -r 's/ /,/g')”

pidof returns a space separated list of pids. lsof -p requires a comma serparated one. This can be solved with sed via: lsof -p `pidof postgres| sed -r 's/ /,/g'` However, the extra pipe seems a ...
0
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0answers
58 views

extract text to csv file from output of reading multiple files into specific rows

I am trying to write a bash script to generate a csv file from text within multiple pdf documents. I have a script for converting pdf to text, but not for generating the csv file. Each text document ...
0
votes
1answer
19 views

Redirect all GnuPG output to /dev/null

I'm doing key generation in a sort of batch mode with GnuPG (don't ask why): echo -e 'addkey\n4\n2048\n120d\nsave' | gpg --command-fd 0 \ --edit-key $master_key_id >/dev/null 2>&1 I ...
4
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1answer
91 views

using pipe to run command in background

I was reading this question on rpi and noticed an interesting line that got me thinking: mkfifo tcp.stream nc -l -p 1234 > tcp.stream | omxplayer --live tcp.stream Notice the io redirection. ...
1
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0answers
45 views

Captive portal detection, popup implementation?

Based on hostapd, I m building a captive portal. - My Linux Machine provides a Wifi access. - iPad's and Android clients-tablets connect this Wifi. Generally, any client OS check if a url is ...
6
votes
1answer
41 views

zsh I/O redirection: redirecting and then piping; what is going on?

Can somebody explain what is going on in this command: echo foo >&2 | grep foo Zsh (5.0.2) prints foo twice. One seemingly to stdout and one to stderr, since running these commands: { echo ...
5
votes
2answers
118 views

Silent GnuPG password request with bash commands

I'm trying to hide the "output" of a gnupg command, but it seems that it is always printed. the command is: echo "thisprogramwørks" | gpg -q --status-fd 1 --no-use-agent --sign --local-user D30BDF86 ...
1
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2answers
68 views

How do I get the output of a program already running?

I have a python program that outputs to stdout and a log file. However, the person I am making this for wants to know if I can set it up so that he can see the output of the file, while it is ...
1
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1answer
53 views

zsh: Disable “file exists:” warning with redirection

How can I override the file exists: warning from zsh? > echo > newfile.txt > echo > newfile.txt zsh: file exists: newfile.txt In these cases I prefer my shell to not complain and ...
9
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2answers
3k views

Does `Segmentation fault` message come under STDERR?

I ran an executable in bash ./code > log It shows occasional error messages on terminal whereas all printf statements go into log file. I re-run it like below ./code >& log Now, the ...
24
votes
1answer
715 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 ...
1
vote
1answer
40 views

How to put “rm -i” in an iteration?

echo "$MOUNTPOINTLIST" | while read onelinefortouch; do touch "${onelinefortouch}testfileforwrite"; done echo "$MOUNTPOINTLIST" | while read onelineforrm; do rm -i "${onelineforrm}testfileforwrite"; ...
2
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2answers
40 views

One-liner to sort and uniq two outputs

I'm currently doing this to sort and uniq the output of two different commands: tshark -r sample.pcap -T fields -e eth.src -e ip.src > hello tshark -r sample.pcap -T fields -e eth.dst -e ip.dst ...
1
vote
1answer
25 views

How to redirect tarsnapper output to /dev/null?

I use tarsnapper's make command for managing tarsnap backups like this: tarsnapper -c /usr/local/etc/tarsnapper.conf make Which works like it should and I get an output like this Creating backup ...
0
votes
1answer
17 views

How to redirect the time a task takes to complete into a log file, given that such task is already redirecting?

I have a shell script running a python task, whose stdout is being redirected to a log file: python script.py >> log.txt I wish to also log the time this task takes to complete, into the same ...
5
votes
5answers
283 views

How to use output redirection dynamically?

I'm trying to add a debug option to a script of mine. Normally I want to hide any output, like warnings etc, so I put >/dev/null 2>&1 behind a lot of commands. Now, when I want to debug my ...
2
votes
1answer
51 views

Piping a file that's being written and discarding the contents?

A software writes its logs on a file ("tonsOf.log"). Those logs are mostly useless and I process them later on with some pattern matching (line by line). So, for say 1 GB of logs, I end up with 40KB ...
3
votes
3answers
36 views

Create 2 similar-name files with content from 2-line output of a command

I perform cmd and it outputs 2 lines of text: $ cmd foo bar I need to write these to: `/long/path/x.{load,conf} Writing to this destination requires superuser privilege, which rules out manually ...
5
votes
3answers
15k views

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 ...
0
votes
2answers
58 views

sponge from moreutils - what's the difference to shell redirect? useful examples?

> brew install moreutils ==> Downloading https://homebrew.bintray.com/bottles/moreutils-0.55.yosemite.bottle.tar.gz ...
0
votes
3answers
49 views

What is `>&` in simple terms? [duplicate]

What does $ command 1>&2 do? As I understand it this runs the command but with the STDOUT redirected to the STDERR. But I'm not sure exactly how >& works. I have seen it as $ command ...
0
votes
1answer
52 views

Why doesn't this simple piping with awk work? [duplicate]

I'm trying to follow this answer but I can't make it work. I simplified it down as much as I could to try work out what's going on (just running this at the terminal for now): rsync --progress -iav ...
-9
votes
1answer
106 views

UNIX homework question regarding piping output, I don't understand what it's asking?

Basically, I need to come up with a command that sends the contents of a file xxx into a program yyy, then the output is piped to the input of another program zzz, where the output is appended to a ...
13
votes
2answers
39k views

How can I assign the output of a command to a shell variable?

I want to assign the result of an expression to a variable and concatenate it with a string, then echo it. Here's what I've got: #!/bin/bash cd ~/Desktop; thefile= ls -t -U | grep -m 1 "Screen Shot"; ...
0
votes
2answers
57 views

Write permissions inside of shell script

I am using a Debian 7 Server. I created a shell script to be executed by crontab to save a mysqldump every day. mysqldump *database* -u *mysql-user* -p*mysql-password* > ...
51
votes
5answers
33k views

How can I send stdout to multiple commands?

There are some commands which filter or act on input, and then pass it along as output, I think usually to stdout - but some commands will just take the stdin and do whatever they do with it, and ...
1
vote
1answer
39 views

Using `perf` repeatedly with file input

perf can be used to analyze the performance of a program. Say you want to test the performance of a program prgrm, with input from a file, you can run: perf stat prgrm < inp.dat Now when you ...
0
votes
3answers
78 views

Throw away standard output and error

I have redircted my ouput using /dev/null in bash script but it is still throwing an error. Code is following ps -p $proc | fgrep $proc> /dev/null if [ $? -ne '0' ] ; then ...... fi below is ...
27
votes
4answers
17k views

Reading lines from a file with bash: for vs. while

I'm trying to read a text file and do something with each line, using a bash script. So, I have a list that looks like this: server1 server2 server3 server4 I thought I could loop over this using ...
4
votes
4answers
440 views

grep command not working in conditional statement

I've a bash script that's supposed to go over all the filenames and print them only those that contain a certain letter (let's say it's 'o'). What I've done: command=`ls -l` for file in $command do ...
2
votes
1answer
140 views

< and << in UNIX /Linux

What are the operators <<and < used for in Linux? For example cat << abc.txt
0
votes
1answer
43 views

need to get the command information over ssh and the input from file

I am writing a script to get the command information of the remote machine usinf while and for loop. PFB the script. But the script ends by giving the single command information only. I have multiple ...
10
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4answers
3k views

Can I make `cut` change a file in place?

The man page doesn't give me much hope, but I'm hoping it's an undocumented (and/or GNU-specific) feature.
1
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0answers
35 views

Inherit IO redirections from a script to another

When I redirect the output of a script within a script, I expect the redirection to be applied to the called script as well as the program called within it. A: ./B 2>> error.log B: ...
2
votes
5answers
2k views

How can I run a process in a terminal window and then hide that window?

I want to run python ~/program/proxy.py in a terminal when I boot up. And then hide this terminal window (because it is just a proxy program, and I don't want to see the debug info). So how can I get ...
11
votes
1answer
4k views

SSH causes while loop to stop

I have finally managed to boil down a problem I have been struggling with for a few weeks. I use SSH with "authorized keys" to run commands remotely. All is fine except when I do it in a while loop. ...
0
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0answers
52 views

How to rewrite the comand using I/O redirections?

Is there any way to rewrite the following command using only I/O redirections and not pipes ? ls -l | grep User | wc -l | tail -l