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

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17
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2answers
399 views

What does 'exec {fd}</dev/watchdog' do in Bash

That is literal, {fd} isnt a placeholder. I have a script that does this, and does not source in anything, nor does it reference {fd} anywhere else. Is this valid bash? exec {fd}</dev/watchdog
0
votes
1answer
22 views

Having extra parameters in piping or redirection

I have two programs and I want to pipe them into each other but they take extra parameters: prog1 <inputfile> <outputfile> min max prog2 <inputfile> <outputfile> min max ...
25
votes
5answers
2k views

Why pipe to cat only to redirect? [duplicate]

I occasionally see things like: cat file | wc | cat > file2 Why do this? When will the results (or performance) differ (favourably) from simply: cat file | wc > file2
3
votes
1answer
25 views

Executing awk on each file found with find, then redirecting the result to a new filename

I am trying to take the results from find and then execute awk to print the first two columns. Then I want to redirect those results to a new file name for each file, using the existing file name with ...
4
votes
1answer
86 views

Capture output without redirection and leave it on terminal too

I need to capture output of a daemon that also includes a on-demand mode and behaves differently depending on if output goes to tty or not. Just redirecting stdout anywhere makes it go into logging ...
0
votes
1answer
34 views

Sort file “foo” and use redirection “>” to save output into the same “foo” file [duplicate]

i have a text file ~/foo: a b c a b c i use sort foo -u, and that works correctly. I can use redirection operator ">" to save output into other file (f.e.: sort foo -u > bar), but when i want to ...
1
vote
2answers
42 views

run command with sudo su in script and redirect stdin and stdout

I need to run command as another user and write to its stdin and read from its stdout. I can run command as another user only via opening new shell: sudo su anotheruser but with new opened shell i ...
5
votes
2answers
43 views

posix placement of stdin redirection (<in cmd vs cmd <in)

I always write stdin redirection after the command, because for me it's more natural to have first the command and then the redirections (if any): some-command < input-file > output-file For ...
4
votes
2answers
47 views

Capturing output/redirection of commands chained by &&

I have a series of commands a,b,c which I am chaining together with &&: a && b && c. I want to catch the output of all the commands to both stdout and stderr. a && b ...
6
votes
1answer
87 views

Extra output on input redirection

I have a folder with three files: $ ls a b c If I pipe the output of ls to wc, I get the right result: $ ls | wc -l 3 However, when I specify the input to wc as the output of ls, I get extra ...
4
votes
1answer
129 views

Pass BASH array to diff like file contents

I have two bash arrays, say: arr1=( 1 2 3 ) arr2=( 1 2 A ) and I want to compare them using diff. How could I pass the arrays as if they were the contents of a file? I tried a few variations, but ...
2
votes
1answer
42 views

Do not wait until the return for Shell redirection

I would like to redirect the output of a script (Python or any other kind) to a file. Easy to do with > or >>. But with these two the output seems to be written in the file only once the script ...
4
votes
3answers
550 views

Behaviour of “|” pipe in linux with “>” output redirection

I am executing command ls > a.txt | sort > b.txt This command is doing the below things : executing ls sorting it creating a.txt and storing sorted output to a.txt creating b.txt , but its ...
2
votes
1answer
35 views

Terminal - redirection of output to file is cutted

I am using command: ./cpp-generator > ~/log.log But when I open the log.log the file is short. It ends in the middle of word. But if I run just: ./cpp-generator in terminal is whole, full ...
1
vote
0answers
51 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 ...
2
votes
1answer
60 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 ...
2
votes
1answer
91 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 / ...
15
votes
4answers
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 ...
1
vote
2answers
102 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
votes
1answer
108 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
votes
4answers
54 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
33 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
votes
0answers
21 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
31 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
votes
0answers
85 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
27 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
votes
1answer
103 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. ...
5
votes
2answers
131 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 ...
6
votes
1answer
50 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 ...
1
vote
0answers
62 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 ...
1
vote
2answers
70 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
vote
1answer
93 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 ...
1
vote
1answer
45 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"; ...
1
vote
1answer
36 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 ...
2
votes
2answers
45 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 ...
0
votes
1answer
24 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
319 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
54 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
37 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 ...
0
votes
2answers
84 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
52 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
58 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 ...
0
votes
3answers
111 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 ...
4
votes
4answers
535 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 ...
1
vote
0answers
39 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: ...
0
votes
1answer
45 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 ...
0
votes
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
0
votes
1answer
39 views

A generic cron wrapper that records all output

I am hoping to write a cron wrapper that records all output in a folder $CRON_LOG_DIR. It would be used as, e.g., follows: * * * * * $CRON_WRAPPER "<job name>" "command" which would record ...
4
votes
1answer
112 views

Problem with paste and standard output in linux

I have two files that I am trying to merge, one file is: linux$ cat temp2 linear_0_A_B linear_0_B_A 103027.244444 102714.177778 103464.311111 102876.266667 103687.422222 103072.711111 103533.244444 ...
0
votes
2answers
58 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* > ...