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
Old 09-25-2018
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:
 

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 Replies)
Discussion started by: anurags
2 Replies

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... (1 Reply)
Discussion started by: srage
1 Replies

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... (12 Replies)
Discussion started by: Wrathe
12 Replies

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` ... (6 Replies)
Discussion started by: dc18
6 Replies

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... (1 Reply)
Discussion started by: rm -r *
1 Replies

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... (8 Replies)
Discussion started by: arcelivez
8 Replies

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... (2 Replies)
Discussion started by: Sundown
2 Replies

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... (2 Replies)
Discussion started by: ronron5477
2 Replies

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... (5 Replies)
Discussion started by: mohtashims
5 Replies
echo(1B)					     SunOS/BSD Compatibility Package Commands						  echo(1B)

NAME
echo - echo arguments to standard output SYNOPSIS
/usr/ucb/echo [-n] [argument] DESCRIPTION
echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output. echo is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi- ronment variables. For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows: o echo your current-working-directory's full pathname o pipe the output through tr to translate the path's embedded slash-characters into space-characters o pipe that output through wc -w for a count of the names in your path. example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w" See tr(1) and wc(1) for their functionality. The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be invoked if the user calls echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the black-slashed escape characters, and ksh's echo() also understands a as the audible bell character; however, these commands do not have an -n option. OPTIONS
-n Do not add the NEWLINE to the output. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
csh(1), echo(1), ksh(1), sh(1), tr(1), wc(1), attributes(5) NOTES
The -n option is a transition aid for BSD applications, and may not be supported in future releases. SunOS 5.11 3 Aug 1994 echo(1B)
All times are GMT -4. The time now is 10:16 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy