Orsdxy

Here is output of:

sudo iwlist scan 2>/dev/null |grep ESSID | sed 's/.*ESSID:"(.*)".*/1/' 2>/dev/null

Yash Shah

CoreFragment

CoreFragment_5G

CoreFragment

dlink

Yash Shah

COMFAST

Appbirds_Technologies

SYMBIOSIS

20096641

CoreFragment_5G

AMBER_AP1

REDWING LABS_5G

While same thing written in script is not working same.

Here is a function in which I used above command.

for ssid_name in $(sudo iwlist scan 2>/dev/null |grep ESSID | sed 's/.*ESSID:"(.*)".*/1/' 2>/dev/null)

do

    echo "$ssid_name";

done

}

I got output like this :

Yash

Shah

CoreFragment

CoreFragment_5G

CoreFragment

Yash

Shah

REDWING

LABS

COMFAST

Appbirds_Technologies

SYMBIOSIS

CoreFragment_5G

REDWING

LABS_5G

Note: when there is a space in putput it take as a new line.

I'm working on ubuntu 18.04.

First, note that it is not one command behaving differently. In your code snippet, standard output is written by two quite different commands.

Your first one prints sed's output, while in your second one:

1. The output of sed is substituted (by the command substitution $(...)) after in;


2. The resulting string is expanded into a list of elements;


3. Each item is in turn assigned to ssid_name and printed by echo.

Expansion in point 2 is performed according to the value of the internal field separator (IFS), whose default value is <space><tab><newline>. Thus, your solution works because it lets for split the substituted string on newlines only.

As an aside on your answer, note that $'n' is not portable - even if that syntax ($'string') is supported in many shells.

You can nevertheless use an assignment like this:

IFS='

'

An alternative construct for processing lines of input is using read in a while loop:

sudo iwlist scan 2>/dev/null | grep ESSID | sed 's/.*ESSID:"(.*)".*/1/' 2>/dev/null |

while IFS= read -r i; do

    printf '%sn' "$i"

done

Here, too, each line of sed's output is split according to the value of IFS - that in this example is set to the null string exactly to prevent any effects of word splitting - but lines would be kept separated by read regardless of IFS.

By adding following line in code before for loop, work perfactly in my case.

IFS=$'n'

Better use a while loop with read instead of a for loop.

sudo iwlist scan 2>/dev/null |grep ESSID | sed 's/.*ESSID:"(.*)".*/1/' 2>/dev/null | while IFS= read -r ssid_name

do

    echo $ssid_name

done

see also https://mywiki.wooledge.org/BashFAQ/001