Questions tagged [io-redirection]
I/O redirection is used in shell scripting. This feature enables to take the output of a command and redirect it as an input for another command. Or command can take the input from a file instead of the keyboard. The whole process helps connect commands in various ways.
0
votes
2answers
93 views
What happens when redirecting with 3>&1 1>/dev/null?
I'm playing around with file descriptors to better grok them and I'm failing to understand the following.
$ grep "..." 3>&1 1>/dev/null
1
12
13
123
321
3
The above does not show in the ...
0
votes
1answer
32 views
Redirecting to both screen and file
I'd like to redirect all of the output of the commands I ran to a file, in addition to having them printed on the screen.
I want this to happen automatically, I don't want to pipe into tee everytime ...
25
votes
3answers
1k views
Is it safe to redirect stdout and stderr to the same file without file descriptor copies?
I start off in empty directory.
$ touch aFile
$ ls
aFile
Then I ls two arguments, one of which isn't in this directory. I redirect both output streams to a file named output. I use >> in order ...
28
votes
5answers
2k views
How to redirect stdout to a file, and stdout+stderr to another one?
How can I achieve
cmd >> file1 2>&1 1>>file2
That is, the stdout and stderr should redirect to one file (file1) and only stdout (file2) should redirect to another (both in append ...
2
votes
1answer
33 views
Difference between Piping and Reading Input
What is the difference between cmd1 > tmp && cmd2 < tmp and cmd1 | cmd2, besides the creation of a tmp file (obviously) ?
If my comprehension of pipe is right, I expect cmd2 to read ...
4
votes
1answer
199 views
stdout and stderr redirection to different files
How can I redirect stdout to 2 different files and stderr to another, different file?
I want something like <my_cmd> 1> file1 file2 2>file3
I know:
<my_cmd> | tee file1 file2 > /...
1
vote
2answers
28 views
Non-Root User SSH Privileged Command with File Piping
I have an a SSH server where root login is disabled. I'm hoping to run a privileged command that will want input from a file I have after being executed. I'm hoping to do all without user interaction ...
0
votes
1answer
33 views
How to send stdin to while loop using redirection operator
Not sure if I used the right words in the title, I am trying to do this:
while read line; do
echo "$line"
exit;
done; <( echo "foo\n"; exit )
but it hangs, I don't think the while loop ...
2
votes
1answer
31 views
Open output of a command using libreoffice
I am running certain commands in a loop and would like to open its output in libreoffice (calc), without storing it.
This is what I have tried:
libreoffice --calc <(process m n)
libreoffice --...
2
votes
2answers
71 views
Difference between `touch file` and `>file`
Say there is an empty directory and I run the commands >file1 and touch file2 while in that directory, but I forget which command created which file.
I don't know what command I ran first and I ...
1
vote
1answer
37 views
File Descriptors and Redirection
Several resources state the file descriptor 0 is connected to the keyboard.
I have learned that echo does not receive input from stdin (or 0).
This feels contradictory to me. When I run echo foo I'm ...
3
votes
1answer
53 views
Exit status of command in pipeline
I have come across this code but cannot understand exec >&p
edit 1 to my understanding :
#! /usr/bin/ksh
exec 4>&1 ## standard output is first saved as file descriptor 4
...
1
vote
2answers
30 views
Capture git output into variable
If I run a command in a subshell, I can collect the stdout into a variable, such as:
var=$(echo 'hello world')
echo $var
Will print 'hello world' as expected.
If I add colour and a new line, this ...
-2
votes
1answer
31 views
Allow redirection for a user [duplicate]
I'm going to permit redirections ">>" and ">" for the www-data user in sudoers
but I can't find this.
2
votes
2answers
57 views
What's the POSIX specification on behavior of built-in commands with redirections and/or piping?
Consider the following commands:
exit > /dev/null
exit | cat
On a few shells (ksh, bash, (d)ash), the behavior is the same: The first command causes the shell to quit immediately, while the ...
1
vote
0answers
23 views
Redirecting input from cron job [duplicate]
I'm using a plugin manager for vim (vim-plug), and have a cron job to perform updates:
vim +PlugUpgrade +qall &>/dev/null; vim +PlugUpdate +qall &>/dev/null
This job occasionally ...
0
votes
0answers
20 views
Redirection vs Process substitution: `echo foo | bar` vs `bar <( echo foo)` [duplicate]
What is the difference between these two constructs,
echo foo | bar
bar <( echo foo )
I thought both of them would set up STDIN the same way. However, that seems to not be the case for me (exact ...
0
votes
1answer
46 views
sed command working only when no outfile is written
I'd like to change this file eq.txt
2018-05-03T18:46:05.050Z 11.8314 44.0586 10 4.3 USGS
2018-05-01T05:16:59.270Z 11.0366 43.2334 10 4.1 USGS
2018-04-26T11:13:20.590Z -5.4109 36.5557 10 4 USGS
2018-...
0
votes
1answer
34 views
Split ssldump output into multiple files for every incoming connection
I am capturing SSL Handshake data using ssldump on the terminal, and using the command
sudo ssldump -i enp0s8 -a -A -H -n -x > new_trace
to output it into a single file. Currently, the output ...
1
vote
0answers
39 views
Shell redirection - follow name, not a descriptor
I have a shell script that is run in the background and the only thing it does is run 1 command, STDOUT of which is being appended to a file.
my_blocking_command >> my_file
I want to stop the ...
0
votes
1answer
36 views
How can I store output in bash variable and suppress output to stderr and stdout? [duplicate]
If i'm doing
oidvalue=$(snmpget -v 2c -c public localhost 1234)
This will store the output of that command in oidvalue, however as it is now, it will print some error to the screen. How can I ...
5
votes
1answer
121 views
Process substitution and redirection using tee
Suppose that you redirect, in bash, the standard output of a command cmd to a file named f.out, and the standard error to f.err, using tee to preserve console printing:
cmd 1> >(tee f.out) 2>...
0
votes
0answers
43 views
Storing output in variable for redirection [duplicate]
My question is about the application of redirecting output and input.
I have a text file that contains 30 or so trackers.
I have a torrent file I'd like to add the trackers to.
transmission-edit is ...
3
votes
2answers
60 views
Output redirection is not working with top piped to grep
When I run this command in Linux:
$ top -b -d 20 | grep "load average" -A 20 > top.log
top.log is always empty.
But when I run this command:
$ top -b -d 20 | grep "load average" -A 20 | tee top....
1
vote
2answers
42 views
Partial Redirection with additional Piping
There's an auto generated file on a remote location that is constantly changing, I can only view the remote file via ssh user@ip cat luckyNumbers it tells me today's lucky numbers and also passes ...
1
vote
0answers
61 views
Log python http server output to file
I want to start a python webserver in the background and log all of its output to file.
Instead the the servers output appears in the terminal.
Even tho i guess this is pretty basic ... I've got no ...
2
votes
1answer
50 views
redirect awk exec results to another folder [duplicate]
Trying to capitalize the content of the files that match the filename pattern "_base.txt"; then output the results to another folder with the original filename plus the "_cap.txt" in the end.
I plan ...
2
votes
1answer
67 views
concurrent processing in bash using process expansion, and redirection
Apart from possible races that have to be controlled by using proper synchronisation, it's possible in bash to feed a data source concurrently into multiple pipelines and collect all their outputs ...
2
votes
1answer
65 views
Redirect standard error of one command to standard input of another command
I wish to redirect standard error of one command to standard input of another command like
g++ filename.cpp 'redirection' less
0
votes
1answer
44 views
“nohup cat” — write the complete content to the log file rather to concatenate file
I used the below command
nohup cat fastp-filtered/OZBenth*_R1.fastp.fq.gz > fastp-filtered-merged4racon/merge_R1.fq.gz > merge_R1.out.log 2>&1 &
but unfortunately, the output went ...
0
votes
2answers
26 views
Overwrite file with stdoutput from cron execution
I have this cron in my crontab
00 01 * * * /srv/python/proj/acquisizione/acquisizioneAOK.sh >> /home/crontab_logs/acquisizioneAOK.out 2>&1; mailx -s "Cron output: acquisizioneAOK" ...
0
votes
1answer
44 views
Permanently redirect stderr to stdout
I have a bash script with many commands, some of which might generate error messages. often, the error messages and output messages are mixed in an apparently incorrect order (for example, I see the ...
0
votes
0answers
34 views
send hex as characters to output to remote end
I'm doing a project for a microcontroller that involves sending and receiving special (non-printable character) data through its serial port.
I found myself a simulator (ucsim) so I can test things ...
0
votes
0answers
23 views
save input and output data has passed in adb
i want save all input and output commands has executed in adbd I tried to pull adbd file in sbin folder and extract it to modify and Implement of the idea to write a few lines for create file and do ...
0
votes
2answers
24 views
Showkey with timestamp
How can I record keyboard actions with the timestamp, either to console, or preferably to a file?
I have showkey output like:
keycode 28 release
keycode 30 press
keycode 30 release
keycode 48 ...
3
votes
1answer
219 views
How to use variables inside back-quotes
I have a bash script that accepts a parameter "$input" and (among other things) directs it into a program and collects the output.
Currently my line is:
OUTPUT=`./main.exe < $input`
But I get ...
0
votes
1answer
79 views
Remote overwrite crontab file with sudo
I'm trying to build a script that automatically takes a file on the remote server and replace with crontab file, but I get permission denied.
My idea is to create a shell function for it:
...
0
votes
0answers
63 views
Redirecting input bash
I have a program, that runs on only one Raspberry Pi, but could be run from multiple other computers (through SSH). When I run my program on the Pi, it runs as expected. To be able to run from crontab ...
5
votes
1answer
822 views
What's going on with this dash '-' thing?
I was trying to export the Python environment requirements and this is what I intended to do:
conda list -e > requirements.txt
However I mistakenly typed this instead:
conda list -e -> ...
0
votes
2answers
74 views
How could I know inside a script if stdout has been redirected for it?
I have a script in ksh; depending whether there is a redirection from the command line, I redirect the output via a exec 1>file. How can I test from inside the script itself if the command calling ...
0
votes
2answers
212 views
Nohup: Redirect stderr to file and dismiss stdout
Per default, nohup writes stdout to nohup.out and dismisses stderr. I would like to have it the other way around:
write stderr to a file and dismiss stdout.
0
votes
1answer
57 views
redirect created files in a directory from command line
I was wondering if there is any way to redirect created files from a .sh script to a specific directory without modifying the script itself but straight from command line.
Let's say:
I've a script ...
2
votes
1answer
113 views
Redirect script output both to console and to log
Take a look on the following
# more /tmp/myscript
#!/bin/bash
echo I AM
echo BIG GUY
echo AND ALSO SMART
# bash /tmp/myscript | tee -a >/tmp/log
why we not get the output from echo in the ...
3
votes
4answers
181 views
Why does `… | sed 's/^/stdout: /'` print on empty stdin when `… > >(sed 's/^/stdout: /')` doesn't?
I'm trying to understand what causes the difference in these 2 constructs that I thought were functionally equivalent:
$ ( echo foo >&2 ) 2> >(sed 's/^/stderr: /') | sed 's/^/stdout: /' ...
0
votes
1answer
49 views
Spaces after io redirection operator? [duplicate]
I've noticed that when writing a shell script, there's a lot of inconsistency in whether people put a space after the I/O redirection operators. For example:
foo >bar.txt
Will work, but so will ...
-1
votes
3answers
47 views
Oneliner for outputting to file only if string is matched (bash)?
I am making a script where I curl a URL and output to a file like this:
curl http://example.com/$1 > $1
Is there any way to make it dismiss anything that doesn't include, say <head>? I ...
21
votes
3answers
2k views
How does this script ensure that only one instance of itself is running?
On 19 Aug 2013, Randal L. Schwartz posted this shell script, which was intended to ensure, on Linux, "that only one instance of [the] script is running, without race conditions or having to clean up ...
1
vote
2answers
177 views
Run parallel command and redirect the output to files with specific name
I can't undestand well how the parallel command works.
I need to run this simple command: (100 times)
curl https://jsonplaceholder.typicode.com/todos/1
curl https://jsonplaceholder.typicode.com/...
5
votes
3answers
249 views
Portable way to invoke tar with a list of files from stdin
I want to create a .tgz from the content of a directory. I also want to strip the leading "./" from the tar'ed content.
I had done this as follows:
cd /path/to/files/ && find . -type f | cut -...
2
votes
1answer
21 views
Ambigious redirect error on different volumes with mysql
i want to import a database with mysql (running with MAMP):
#! /bin/bash
# variables
currdir=$PWD
dbname=TEST
dbuser=root
dbpass=root
dbpath="/applications/MAMP/Library/bin"
exname=database
if [ "$1"...
