[Linux 常見問題] Bash - How to loop over the lines of a file?

Source From Here 
Question 
Say I have this file: 
- data.txt 

view plaincopy to clipboardprint?

1. hello  
2. world  
3. hello world  

This program: 
- test.sh 

view plaincopy to clipboardprint?

1. #!/bin/bash  
2.   
3. for i in $(cat $1); do  
4.     echo "tester: $i"  
5. done  

Execution result: 

# ./test.sh data.txt
tester: hello
tester: world
tester: hello
tester: world

I'd like to have the for iterate over each line individually ignoring whitespaces though, i.e. the last two lines should be replaced by: 

tester: hello world

How-To 
With for and IFS (internal field separator): 

view plaincopy to clipboardprint?

1. #!/bin/bash  
2. IFS=$'\n'     # Make newline the only separator  
3. set -f              # Disable globbing  
4. for i in $(cat "$1"); do  
5.     echo "tester: $i"  
6. done  

# echo "$IFS" | cat -vte // Original IFS includes "\t", " " and "\n"
^I$
$
# ./test.sh data.txt
tester: hello
tester: world
tester: hello world

Or with read (no more cat): 

view plaincopy to clipboardprint?

1. #!/bin/bash  
2.   
3. while IFS= read -r line; do  
4.   echo "tester: $line"  
5. done < "$1"  

Supplement 
* What is IFS in context of for looping? 
* Linux tip: Using the read command