Questions tagged [stdin]
stdin is the name of the default input file descriptor of a process. Since there is really nothing special about `stdin`, you *should not* use this tag. Use the [io-redirection] tag for questions on how to redirect input, use [file-descriptors] for questions on how to manage file descriptors, use [lock] for questions of file locking, and use [files] for general questions on file operations.
309
questions
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1
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154
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When and where are the standard in, out, and error file descriptors first opened in linux?
Where are stdin, stdout, and stderr (the fds) first opened? Is it the kernel that does it? And when and where are the symlinks /dev/std{in,out,err} made? Where is the code that does it?
I assume it is ...
- 39
0
votes
1
answer
110
views
Is standard streams just variables?
When I run command, e.g. test -l --hello check:
shell save the command to variables, $0="test", $1="-l", $2="--hello" and $3="check"
shell execute ...
- 27
0
votes
0
answers
25
views
How to check if stdin have data without IO blocking (docker)?
If I execute echo this | docker run -i alpine cat, I get this.
If I execute docker run -i alpine cat, I get blocked terminal, because cat reads stdin, but there is nothing there.
I can check opened ...
- 111
0
votes
0
answers
32
views
Simultaneous input from fifo and terminal in bash
I am running ffmpeg inside a script and I want to be able to quit ffmpeg either by pressing 'q' in the terminal it's running in (default behaviour) or by inputting 'q' into a fifo file, whichever I ...
0
votes
1
answer
37
views
Calling vim in subprocess after running cat
I am trying to create a bash function vim_run which operates as follows:
user pipes command output into vim_run
user can edit output
user exits vim and the contents of that buffer are now executed ...
- 3
1
vote
1
answer
54
views
Creating PKCS#12 container from input from stdin
I want to create a PKCS#12 (a.k.a PFX) container for a private key and a certificate using openssl.
My key and cert are contained in a single (unecnrypted) file:
$ cat d.pem
-----BEGIN CERTIFICATE-----...
- 290
0
votes
0
answers
31
views
Bash script ignores all terminal input following an underscore [duplicate]
Goal
My server manages jobs using SLURM. Each job in the queue has a job ID, which can be either a single integer or two integers separated by an underscore, e.g., 123_4. You can use scontrol show job ...
- 1
1
vote
2
answers
157
views
Capture and redirect stdin (user input) for runtime of script
I can redirect the stdout/stderr of everything in a script like this:
#!/bin/bash
exec > stdout_file
echo example
But now I want the stdin of the whole script to be written into a file. I tried it ...
- 111
2
votes
1
answer
394
views
Stop stdin while command is running
How to stop stdin while command is running in ash (not bash)?
For example:
sleep 10
type echo hello while sleep is still running
observe hello is in stdout after sleep finishes
Desired:
sleep 10
...
- 376
0
votes
1
answer
43
views
Why are commands reading from /dev/stdin get a status "[1]+ Stopped" when sent to background?
I have tried running the following commands:
cat
base64 /dev/stdin
md5sum /dev/stdin
tail /dev/stdin
In all cases when I do:
^Z
$ bg
$ jobs
I get the status: [1]+ Stopped instead of [1]+ Running.
...
- 779
0
votes
3
answers
280
views
Why does < exist to redirect to stdin? [closed]
Question
Why do shells implement alternative means like <<<, < <(command) and < /dev/fd/* to redirect something to stdin when pipes do exist?
Example
The | way (classic pipes)
echo '...
- 337
0
votes
1
answer
133
views
Pipe zip & unzip together to form the identity function
Update: On closer inspection of the man page it appears that it is not yet supported by unzip to read archives from standard input. The man page refers the user to funzip instead. I guess this makes ...
- 131
5
votes
3
answers
304
views
Processing a continuous single line of data with stream processing in bash pipeline?
I am debugging an embedded server that outputs a continuous single line of text to a specified network port. There is no newline anywhere in the stream but it is text data and I would like to format ...
- 193
0
votes
1
answer
114
views
Detect whether input is coming from the terminal
I have a shell script that can read from a file or from standard input. Currently, if you don't give it a file or pipe text into it, it starts accepting input at the command prompt.
Instead, I would ...
- 1,822
1
vote
1
answer
237
views
How might I only write stdout to file if exit code is 0?
The sponge command "soak[s] up standard input and write[s] to a file", which lets us pipe from and to the same file. I want to do something similar, where I pipe to a sponge-like utility, ...
- 123
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votes
0
answers
20
views
Can I safely start reading a file while it is being sent over scp?
I am copying a large sql backup to a server using scp. It takes a couple of minutes to copy. When it has finished copying, I plan to restore a database using that backup using (modulo details) mysql &...
- 329
0
votes
3
answers
240
views
save tar stdout to files using pipelines
I try to download a archive to a remote computer using SSH and also extract the archive on the remote client due to it having better performance.
I have a very simple script that downloads the archive ...
- 111
42
votes
1
answer
6k
views
What's wrong with var=$(</dev/stdin) to read stdin into a variable?
We've seen a few posts here lately that use this:
var=$(</dev/stdin)
in an attempt to read the shell's standard input into a variable.
That is however not the correct way to do it on Linux-based ...
- 525k
0
votes
4
answers
206
views
Bash: interactively enter and save large html block into a variable from the terminal
This is simple
#!/bin/bash
echo "What is your name?"
read name
echo "Your name is: $name"
But what if I don't want to treat a name but a large HTML code block with nested tags and ...
- 111
4
votes
1
answer
823
views
Why I need to type press Enter key to finish this command? [duplicate]
I'm a new Linux user and I was doing some experiments and trying to understand Process Substitution. I believe I already have a basic understanding of it. But here is a case that I don't know why. I'm ...
- 965
0
votes
1
answer
1k
views
Send more than one line to an executable using bash
So python has a convenient function as part of pwntools where one can sendline() to an executable. How can I emulate this functionality in bash?
Example
#whatever.py
x = input("First input please:...
- 325
0
votes
1
answer
40
views
Text (from file) to running program
I have degenerative bone disease in my hands and would like to make YouTube videos that look like I am typing in a text editor such as Sublime or Kate (KDE).
How can I make a text editor receive a ...
- 157
0
votes
0
answers
1k
views
Bash: echo command into tty
I've a service written in Python that can receive commands and does things, here is how it is built:
print("\nWelcome!\n")
for line in sys.stdin:
cmd=line.rstrip()
...
- 721
0
votes
1
answer
99
views
How to make a list of values out of a webpage?
In this webpage there is a list of MediaWiki special pages (i.e. pages of the Special: namespace) and I wish to make a simple text list of all these names automatically.
I assume that a matching ...
- 113
1
vote
1
answer
376
views
Configure zsh to display my stdin in green
I wanted a simple way of displaying errors in red, and inputs in green in zsh.
I found this response, that works well, but it doesn't implement the input color. I'm not really a unix developper, so I ...
- 41
4
votes
1
answer
1k
views
sed: replace multi-line block with standard input
Given is input_file:
1
2
START
foo
END
3
Goal is to replace content inside including START ... END block with multi-line content from stdin:
1
2
hello
world
3
What I tried:
sed '/^START$/,/^END$/d;...
- 43
1
vote
1
answer
467
views
How do I read n bytes from file descriptor 0 to a file? Bytes can be any value [duplicate]
I need to read a specific number of bytes from fd0 and write them to a file. The bytes can have any value.
I assume I can't use dd since it stops at the EOF byte. Using if=/dev/stdin won't work since ...
- 13
0
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0
answers
30
views
How does a tool like grep recognize end-of-input when reading from stdin [duplicate]
How does a tool like grep know when the end of file is reached, when reading from stdin (like in foo | grep)?
The EOF byte could belong to the original file, so it can't rely on that. Does it rely on ...
- 13
1
vote
2
answers
664
views
Dangers of piping to stdin of process in another terminal
Out of malicious curiosity I opened 2 terminals, each running the bash shell. In the first I type :
$ echo $$
11458
and in the second :
$ echo -n "echo this command" >> /proc/11458/fd/...
- 313
0
votes
1
answer
436
views
Pipe output of two commands into another script as arguments
ntopng can handle multiple network interfaces and I've a script that takes the name of the interface and outputs it in to stdout. I can pipe this output into ntopng
my_packet_tracer.sh | ntopng -i -
...
- 155
2
votes
2
answers
3k
views
wc command with no FILE argument (reading from standard input)
Regarding wc (word count) command... I am trying to understand the following (from man wc which I have quoted below plus added a longer quote at end of my question)
With no FILE, or when FILE is -, ...
1
vote
1
answer
2k
views
How to use clipboard-cli on Wayland?
I am using this module gtts-cli for text to speech conversion.
more info here-> https://gtts.readthedocs.io/en/latest/cli.html
Basic syntax is
$ gtts-cli 'hello' --output /tmp/hello.mp3 && ...
- 27
0
votes
1
answer
795
views
stdin buffer - what is it?
While reading the "Kubernetes in Action" book I saw the following excerpt (p. 124):
Listing 5.2 Enabling standard input for a container
apiVersion: v1
kind: Pod
metadata:
name: kiada-...
- 271
6
votes
4
answers
2k
views
How to visualize EOF in bash
/dev/null is a special Linux file which discards everything written to it, and which provides EOF when read.
I would like to read /dev/null to obtain and visualize this EOF. If I try:
$ cat /dev/null |...
- 4,821
2
votes
1
answer
234
views
No output: busybox find . -exec sh -c ' readlink -f "$1" | tail -n +2 ' sh {} \;
I got access to only Busybox 1.31.1
I originally wanted to remove the current working directory of my output (the single dot).
Example:
/prueba$ ls
uno dos tres
When I:
$ busybox find .
.
./uno
./dos
...
- 143
2
votes
1
answer
2k
views
Prompt for ssh password if needed, then pipe into the ssh session
As an experiment, I'm trying to write a script where I pipe a ZIP file into unzip on my server via ssh, however, what if I didn't have my SSH keys set up, and was prompted for a password? I'd still ...
- 21
0
votes
1
answer
232
views
in AIX ksh the command "mail" reads from STDIN and stops a loop wherein it is
using ksh on an AIX 7.2 system
I have the following inputfile:
line1
line2
line3
I have the following code (rather simplified)
cat infile | while read strA ; do
echo "strA: $strA"...
- 1
4
votes
2
answers
343
views
In GNU screen, how to read from stdin and save into a register?
I'm using GNU screen and I want to save input from stdin into a register to slowpaste it later. I tried a workaround with a temp file (which I can read into a register with readreg afterwards) and to ...
- 2,980
2
votes
2
answers
2k
views
Send keypress to non-GUI program
I try to manipulate ssh process by another process.
Image i run ssh root@XXXX and the pid is 12345. I want to run a program to tell the ssh session to run ls command, i tried echo ls > /proc/12345/...
- 123
1
vote
1
answer
335
views
How do I keep stdin open when launching an executable via a Desktop Entry File (i.e. .desktop)?
I have a desktop application that relies on stdin.
If I run it in the terminal, it runs great and quits when stdin closes (CTRL+D). I also have a systemd activation socket set up which can launch ...
- 12.7k
1
vote
2
answers
1k
views
Spawn a terminal and redirect its stdout to original process
I'm trying to spawn a new terminal, execute a few commands and pipe their output to stdin of the original process. A mwe of what I'm trying to do is the following bash one-liner:
$ xterm -e sh -c &...
- 387
5
votes
1
answer
1k
views
How to redirect a command's `stdin` as well as `stdout` to the output
Suppose I have the Python script:
#!/usr/bin/env python
input('Y/n: ')
print('Next line')
After I press Y, I want both the terminal and my output.txt containing:
Y/n: Y
Next line
Running the ...
- 723
8
votes
2
answers
5k
views
KeepassXC-cli: Send password to stdout
I would like to authenticate to neomutt using keepassxc. I could not find a way to send password to neomutt's stdin. How can i do that ?
I imagine something like this:
keepassxc-cli exportpass ...
- 1,205
1
vote
1
answer
659
views
Use piped content in a python script passed as heredoc
I am aware that here-doc goes to stdin. I saw that here-doc takes precedence in going to stdin before what's coming from the pipe (see below).
But maybe there's a trick to make it work?
All in all I ...
- 21
1
vote
1
answer
598
views
How to access stdin/stdout from detached program?
I am trying to understand how to access stdin an stdout for a process.
I have a remote machine accessible only by SSH and I want to run a terminal based program in the background. That is, I fire up ...
- 111
1
vote
2
answers
513
views
Is there any way to de-couple stdin into multiple input sources?
I am looking for a way to have two stdins to a bash script, namely one that is interactive and another which could leverage redirection
Say I need to invoke a program which asks for credentials of the ...
- 11
1
vote
2
answers
2k
views
How to pipe a number into bc elegantly?
Is there a more elegant way than using xargs -Ix for the following?
echo "283" | xargs -Ix bc -l -e "scale=2; l( x )/l(10)"
- 166
8
votes
1
answer
835
views
Why is the file descriptor opened and read only once?
Why can it be used only 1 time when we open the file descriptor ourselves and redirect it to stdin?
Please take a look at the example below to understand what I want to say. After reading it once with ...
- 1,310
0
votes
1
answer
30
views
What would the value of hyphen actually look like in this instance used to refer to stdin for this archive command?
I am following a guide to learn terminal commands and have encountered the use of hyphens to refer to stdin in the following command used to find all files named 'file-A' within the directory ...
- 115
1
vote
1
answer
487
views
sh script, loop until stdin is closed - how can I test it?
I'm trying to pas an input stream through a pipe and want to catch a condition in which a downstream pipeline program might fail in which case I need to restart it. So I put it into a loop:
step1 |...
- 399