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

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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
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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
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1answer
23 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
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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
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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
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2answers
42 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
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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
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1answer
86 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
127 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
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1answer
40 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
548 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
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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 ...
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0answers
50 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
59 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
90 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
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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 ...
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2answers
101 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
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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
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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'" ...
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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
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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 ...
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81 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
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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
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1answer
102 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
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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
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1answer
49 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 ...
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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 ...
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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
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1answer
92 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
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1answer
44 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
317 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 ...
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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
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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
109 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
533 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 ...
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0answers
37 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
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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
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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
0
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1answer
38 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* > ...
1
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1answer
56 views

How to create dynamic process substitution based on the input (multiple FIFOs)?

I'm trying to create multiple process substitutions based on the output from the other command, however I'm not sure how I can achieve that. As sample scenario, I've given list of files: touch a.txt ...