Sponsored Content
Top Forums UNIX for Beginners Questions & Answers Behaviour of echo commands used by Linux admins Post 303023888 by kraljic on Tuesday 25th of September 2018 07:51:22 AM
Old 09-25-2018
Behaviour of echo commands used by Linux admins

version info : Fedora 28 (Kernel version: 4.16.12-300)
shell : bash

Using echo command , if I redirect a text like "Chocolate" to a file , all the contents in the file are overwritten as shown below.

Code:
[root@john215 ~]# cat /tmp/someTest 
Hello world 
One more Hello world 
myLine3 
 
[root@john215 ~]# echo Chocolate > /tmp/someTest 
[root@john215 ~]# cat /tmp/someTest 
Chocolate 
[root@john215 ~]# file /tmp/someTest 
/tmp/someTest: ASCII text

But, I have seen Linux system admins using echo commands like below to scan for new LUNs.

Why is "/sys/class/scsi_host/host1/scan" file not being overwritten with "- - -" or "1" by the echo commands below ?

Code:
 
# echo "1" > /sys/class/fc_host/host/issue_lip 
# echo "- - -" > /sys/class/scsi_host/host1/scan

Source:

1.8. Scanning Storage Interconnects - Red Hat Customer Portal


Code:
# file /sys/class/scsi_host/host1/scan 
/sys/class/scsi_host/host1/scan: writable, regular file, no read permission

 

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
xpacmdnew(3)							SAORD Documentation						      xpacmdnew(3)

NAME
XPACmdNew - create a new XPA public access point for commands SYNOPSIS
#include <xpa.h> XPA XPACmdNew(char *class, char *name); DESCRIPTION
Create a new XPA public access point for commands that will share a common identifier class:name. Enter this access point into the XPA name server, so that it can be accessed by external processes. XPACmdNew() returns an XPA struct. It often is more convenient to have one public access point that can manage a number of commands, rather than having individual access points for each command. For example, it is easier to command the ds9 image display using: echo "colormap I8" | xpaset ds9 echo "scale log" | xpaset ds9 echo "file foo.fits" | xpaset ds9 then to use: echo "I8" | xpaset ds9_colormap echo "log" | xpaset ds9_scale echo "foo.fits" | xpaset ds9_file In the first case, the commands remain the same regardless of the target XPA name. In the second case, the command names must change for each instance of ds9. That is, if a second instance of ds9 called DS9 were running, it would be commanded either as: echo "colormap I8" | xpaset DS9 echo "scale log" | xpaset DS9 echo "file foo.fits" | xpaset DS9 or as: echo "I8" | xpaset DS9_colormap echo "log" | xpaset DS9_scale echo "foo.fits" | xpaset DS9_file Thus, in cases where a program is going to manage many commands, it generally is easier to define them as commands associated with the XPACmdNew() routine, rather than as separate access points using XPANew(). When XPACmdNew() is called, only the class:name identifier is specified. Each sub-command is subsequently defined using the XPACmdAdd() routine. SEE ALSO
See xpa(7) for a list of XPA help pages version 2.1.14 June 7, 2012 xpacmdnew(3)
All times are GMT -4. The time now is 05:46 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy