shell basics 7- field separator and iterator

What is an internal field separator

Internal field separator (Internal Field Separator, IFS) is an important concept in the shell scripting. Processing
text data, it is no small role.
As a separator, IFS has a special purpose. It is an environment variable, which holds the character used to separate. It is when
the default shell environment delimited string before use. We can see the $ IFS variable, so to see this separator.

[root@dns-node2 tmp]# echo $IFS

Replace the separator thereby slicing string

Consider a situation: we need to iterate through a string type or comma-separated value (Comma Separated Value, CSV)
word. If the former, use IFS = ""; if the latter, using IFS = ",".

[root@dns-node2 tmp]# cat  testIFS.sh
#!/bin/bash
data="name,age,sex,telphone_number,location"
oldIFS=$IFS
IFS=,
for i in $data
do
    echo item: $i
done
IFS=$oldIFS

[root@dns-node2 tmp]# sh  testIFS.sh
item: name
item: age
item: sex
item: telphone_number
item: location

The above is not used to do awk specified delimiter, IFS to directly change the slicing string, it badly.
Then take a look at the following example below:

[root@dns-node2 tmp]# cat testIFS2.sh
#!/bin/bash
line="root:x:0:0:root:/root:/bin/bash"
IFS=":"
for i in $line
do
    echo $i
done

[root@dns-node2 tmp]# bash testIFS2.sh
root
x
0
0
root
/root
/bin/bash

tips

May be used to output echo sequence, for example the following data:

[root@dns-node2 tmp]# echo {1..500}
[root@dns-node2 tmp]# echo {a..z}
[root@dns-node2 tmp]# echo {A..z}