Questions tagged [read]

`read` is a shell utility used for reading strings from the standard input stream, or from a file descriptor.

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Linux AHCI/ATA read errors not reported

After a recent OS upgrade (to current Tumbleweed, Linux Kernel 4.16.0 from April 4th), when reading from a faulty hard disk or from damaged/scratched DVDs, I don't get anymore read errors in the ...
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0answers
117 views

'less' with header line kept at the top

Just like this question: I want to open a file with e.g., less -Sx32 file.dat, but as I scroll down, keep the top line locked in place. How can I do this with less?
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1answer
139 views

Monitoring file reads for cache warming

After adding more memory to my Linux machine I was tempted to use the cache more agressively. The thing is: I boot up my machine, go to bathroom, come back and log in. It takes like half a minute to ...
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1answer
43 views

Reading data from serial port

FYI I am running busybox. I am able to send data to my ttyS1 using the following command: stty -F /dev/ttyS1 speed 115200 cs8 -cstopb -parenb -echo echo -en 'data here' > /dev/ttyS1 But when I ...
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0answers
178 views

Max transfer size in SG_IO/SG_ATA_16

I need to pass a direct, raw ATA request to a hard drive (0x25, READ DMA EXT), to disobey max sector count (long story), and to bypass all possible OS caches, buffers, reorderings et al. ...
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0answers
709 views

High iowait while the throughput and IOPS are low

I'm new to programming & Linux. After I finished my programs(do some IO), I found iowait is very high(~65%) while the throughput(~5M/s read + ~5M/s write) and IOPS(50~100 QPS) are low. iostat -...
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98 views

evaluating dual blocking commands in a bash condition statement

I am attempting to write a loop that refreshes a terminal either 1. when the file(s) have been modified, or 2. When user input is detected second interval. I know how to do one at a time, like so: ...
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1answer
52 views

Python `read -n1 var`?

Is there a Python 3 module that allows to input a single character, without having to press Enter afterwards? Like Bash's read -n1 var?
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278 views

Random write on DISK benchmark shows high read rate on iostat

I am running a random write benchmark directly on some disks (HDD & SDD) and I am getting some weird output data on the iostat monitor. Besides the usual write rate, there is a read rate that I ...
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3answers
675 views

Printing a line at a specified offset in a file

I have a file with 50 characters on each line and 50 lines. Each line of the file contains arbitrary letters. I want to specify a character sequence number (ex: 52) and have the appropriate line of ...
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0answers
130 views

Responding to prompts automatically?

Lets say I have a script called RPS that simulates rock paper scissors. For example lets say I run the script with "$sh RPS". The script will echo "paper" and then prompt me for an input. Obviously ...
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0answers
35 views

Read numbers from a txt file as the variables, each time for each line

I just began learning to write c-shell scripts. (#! /bin/csh) I have a txt file like this. (contain four parameters of three cases) 1 2 3 4 5 6 7 8 9 10 11 12 And I want to read this file each ...
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5 views

Sniffing to Signal Coming From a Controller to Raspberry Pi

I am working on a project on Raspberry Pi to send commands to a controller. I am using ttyUSB0 port of the Rpi with RS485 to communicate with controller. Normally, there is a dos program which does ...
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1answer
55 views

Filter script output during runtime

I have a script that runs about 10 other scripts in the background that constantly generate new output. I would like to keep that initial script running and be able to simply type in it to filter all ...
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0answers
39 views

How to create program that automatically removes old lines

Say I have a simple pipeline: receive-data | write-to-file --max-lines 500 -f <file> how can I implement a program write-to-file where the max number of lines is 500 or some number? (It can ...
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0answers
45 views

append to a string in loop not working

I have a ksh script, where I am trying to read from file in a loop and append certain values to each line in the file. It is not working. Below is the code: Code snippet: input="$...
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2answers
668 views

How to read stderr from the process running in the background?

I wanna send the daemon into the background and only continue my script execution when the daemon outputs the particular line to the stderr, something among the lines: # Fictional daemon { for x ...
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0answers
118 views

Alternative to `while read line` for pipe

I have this: export var=1 kbc get pods -o=json | jq -r '.items[].metadata.name' | while read line; do echo "$line"; done; kbc get pods -o=json | jq -r '.items[].metadata.name' | xargs echo var=$...
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1answer
67 views

while read loop seems to terminate after the first line, when using two pipes?

#!/usr/bin/env bash set -euo pipefail while read -r line do echo "line via echo:" echo "$line" echo "line via sed:" sed 's/w/f/g' | sed 's/f/zzzzz/g' <<< "$line" done < /dev/...
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1answer
88 views

How to read only the last line of a live input stream in a while read loop

I have a very simple bash script that synchronizes data to a USB key as soon as new files appear. It is poorly written but it works, however I want to minimize CPU time so I used sleep but since I use ...
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1answer
506 views

Why does bash 'read' exit with status 1?

From an answer to "Bash script doesn't see SIGHUP?", I've got the following in my script: while true; do read; done And, usually, this works fine. However, when run from (tl;dr) ... something else, ...
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25 views

Reading existing screen displayed values

Using BASH, is there a way to capture characters that on currently on the screen? More specifically, I need to display a screen, with what is currently in a variable, and allow the user to cursor ...
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97 views

What is the difference between nfs_readpage and nfs_read?

Does every nfs_read always has a nfs_readpage request or does both are exclusive? Please explain. I am trying to understand this: http://www.fsl.cs.stonybrook.edu/~mchen/mountstat-format.txt
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1answer
75 views

read 1 or several lines in bash - make it work when pasting (in addition to typing manually)

I read multiple answers with varying complexities. Most are working well when the input is typed manually. For example: https://stackoverflow.com/a/20913871/1841533 . Here is my sample code, very ...
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1answer
43 views

How to backup /user/home with some requirements?

I'm currently studying scripting and I need to create an script to back up the /user/home using .bz2 compression. My teacher wants the person running the script to select the user to backup and the ...
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1answer
128 views

Cannot get interface information using read

The following link has a script to get system information: z3bra' blog Specifically, network() { read lo int1 int2 <<< `ip link | sed -n 's/^[0-9]: \(.*\):.*$/\1/p'` if iwconfig $...
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156 views

reading dates from process substitution using awk. Issue with field separator, splitting tokens incorrectly

I have the following code, thanks to @Janis for the help with the process substitution. Also, apologies for creating a new question, I haven't received any recent replies on the thread of my previous ...
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1answer
433 views

How to Interactively ask a user to change Permissions for a Specified File

I need to create a script that will allow a specified file to have its permissions changed interactively by asking the user if they would like to enable Read, Write and/or Execute one by one for each ...