Behaviour of echo commands used by Linux admins Post: 303023904

Sponsored Content

Top Forums UNIX for Beginners Questions & Answers Behaviour of echo commands used by Linux admins Post 303023904 by Peasant on Tuesday 25th of September 2018 10:49:30 AM

09-25-2018

Moderator

This is due sysfs being pseudo filesystem, as procfs is as well.

It's actually an interface from kernel space to user space which allows you to manipulate various options regarding your hardware or operating system values.
Options such as fibre rescan, ip4 forwarding etc are all controlled by user using those pseudo file systems.
A lot of those options have real backed configuration files (such as /etc/sysctl.conf) which will apply those on boot.

That file system is created after system is booted (or on request) and populated with your device files.
For instance, if you add additional fibre card, a sysfs will be populated with additional hierarchy for that card.

An actual echo command is predetermined, if you issue anything else error will be written.

Take the following example from my PC at home :

Code:

root# echo "- - -" > /sys/class/scsi_host/host1/scan
root# tail -f  /var/log/messages
kernel: [ 6598.240883] ata2: hard resetting link
kernel: [ 6598.555362] ata2: SATA link down (SStatus 0 SControl 300)
kernel: [ 6598.555382] ata2: EH complete
root# echo "gibberish" > /sys/class/scsi_host/host1/scan
-su: echo: write error: Invalid argument

Hope that helps
Regards
Peasant.

These 2 Users Gave Thanks to Peasant For This Post:

Peasant

View Public Profile for Peasant

Find all posts by Peasant

9 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Longer commands and strange behaviour on ksh

Hi, I was trying to customize this archaic HP-UX box. only shell available is ksh and that too seems to be pretty old and doesn't completely conform to what I read on the web about ksh. Anyway here are my issues: - I wanted to have a dynamic title on xterm or dtterm. I put the following lines...

2. Shell Programming and Scripting

Wierd behaviour setting stty echo

Hi all, Encountered a wierd behaviour which I am unable to understand. I have a function doing the follow: function RETRIEVE_PASSWORD { if (( $DC_ACCOUNT )) then clear printf "\nEnter Password for ${ConfiguredUser}" printf...

3. Shell Programming and Scripting

SSH, Remote Commands and echo, oh my!

So, HostB has a SSH trust via pre-shared keys from HostA. HostA> ssh HostB hostname HostB HostA> ssh HostB echo `hostname` HostA HostA> ssh HostB 'echo `hostname`' `hostname` HostA> ssh HostB "echo `hostname`" HostA HostA> ssh HostB echo $PS1 user@HostA:$PWD HostA> ssh HostB...

4. Shell Programming and Scripting

Advice using cut & echo combination commands

Hi, I am cutting data from a fixed length test file and then writing out a new record using the echo command, the problem I have is how to stop multiple spaces from being written to the output file as a single space. Example: cat filea | while read line do field1=`echo $line | cut -c1-2` ...

5. Linux

Linux/Weblogic Admins?

Please forgive me if I've chosen the wrong forum... but I'm just wondering how likely it is to find a Linux sys admin with a vast BEA Weblogic skillset or vice versa (a Weblogic admin with vast Linux admin skills)? The reason I ask is because our Linux Sys Admin is leaving for a position with...

6. UNIX for Dummies Questions & Answers

Having a hard time with the sed/echo commands?

Hello, well what I'm trying to do is to remove underscores from filenames and leaving empty spaces instead: arturas@Universe:/windows/Center/training$ ls big_file failas su shudu arturas@Universe:/windows/Center/training$ a=big_file arturas@Universe:/windows/Center/training$ mv $a `echo...

7. Shell Programming and Scripting

echo and grep commands

Hey im new in this...anything will be helpful... The user will input the word or phrase .... I want to search the user input in file (by lines) but not all then with this line search on another file ( with the specific line) and show to the user. Example: file1.txt ======= a aa aaa...

8. UNIX for Dummies Questions & Answers

Echo out running commands

Is there any way in a script to print out the commands being ran? In DOS script, there is the "@echo on" and "@echo off". so I have a script like this: #!/bin/ksh echo "hello there. moving files." <turn on echoing here> cp thisfile.txt thatfile.txt cp whatfile.prop whyfile.prop <turn...

9. Shell Programming and Scripting

Strange behaviour on my Linux Server.

Hi, I keep getting this error when i run my script: No matter how many times i run this rm -rf /siebel/sfs/tmp/dump it succeeds when i expect it only the first time to succeed becoz i expect the second to fail as the directory should be gone in the first run. i had earlier mentioned...

LEARN ABOUT DEBIAN

echo

ECHO(1) 							   User Commands							   ECHO(1)

NAME

       echo - display a line of text

SYNOPSIS

       echo [SHORT-OPTION]... [STRING]...
       echo LONG-OPTION

DESCRIPTION

       Echo the STRING(s) to standard output.

       -n     do not output the trailing newline

       -e     enable interpretation of backslash escapes

       -E     disable interpretation of backslash escapes (default)

       --help display this help and exit

       --version
	      output version information and exit

       If -e is in effect, the following sequences are recognized:

       \     backslash

       a     alert (BEL)

            backspace

       c     produce no further output

       e     escape

       f     form feed

       
     new line

       
     carriage return

       	     horizontal tab

       v     vertical tab

       NNN  byte with octal value NNN (1 to 3 digits)

       xHH   byte with hexadecimal value HH (1 to 2 digits)

       NOTE: your shell may have its own version of echo, which usually supersedes the version described here.	Please refer to your shell's docu-
       mentation for details about the options it supports.

AUTHOR

       Written by Brian Fox and Chet Ramey.

REPORTING BUGS

       Report echo bugs to bug-coreutils@gnu.org
       GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
       General help using GNU software: <http://www.gnu.org/gethelp/>
       Report echo translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright (C) 2011 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       The full documentation for echo is maintained as a Texinfo manual.  If the info and echo programs are properly installed at your site,  the
       command

	      info coreutils 'echo invocation'

       should give you access to the complete manual.

GNU coreutils 8.12.197-032bb					  September 2011							   ECHO(1)