IFS and Loops in Linux Bash Script

The shell has oneenvironmentvariable, which isnamedtheInternal Field Separator(IFS). This variable indicates how the words are separated onthecommand line. TheIFSvariable is, normally or by default, a whitespace (”). TheIFSvariable is used as a word separator (token) for theforcommand. In many documents, IFS can be any one of the white spaces,:,|,:, or any other desired character. This will be useful while using commands such asread,set, andfor. If we are going to change the defaultIFS, then it is a good practice to store the original IFS in a variable.

Later on, when we have done our required tasks, then we can assign the original character back to IFS.

In the following  for_16.sh script, we are using: as the IFS character:

for_16.sh

#/bin/bash 
cities=Delhi:Chennai:Bangaluru:Kolkata 
old_ifs="$IFS"           # Saving original value of IFS 
IFS=":" 
for place in $cities 
do 
      echo  The name of city is $place 
done 

Let’s test the program:

$ chmod +x for_16.sh
$ ./for_16.sh

The following will be the output after executing the preceding commands:

Output:

The name of city is DelhiThe name of city is ChennaiThe name of city is BangaluruThe name of city is Kolkata

By default, the original inter-field separator is a whitespace. We have saved the original IFS in the old_ifs variable. We assigned a colon : and an IFS in the script. Therefore, we can use : as an inter-field separator in our test file or text string.