mjhjmtu

To sum it up....

This works:

awk 'BEGIN FS=":"; 
 print $1 $3 $5; ' /etc/passwd

But this doesn't:

awk 'BEGIN FS=":"; 
 echo $1 $3 $5; ' /etc/passwd

I would like to know why.

The structure of awk execution is: pattern action statements

Actions

    Action statements are enclosed in braces, and . Action statements
consist of the usual assignment, conditional, and looping statements
found in most languages. The operators, control statements, and
input/output statements available are patterned after those in C.

• 
  

  print is I/O statement of awk.

  
  
  

  From manpage:

  
  
  

  print Print the current record. The output record is terminated with the value of ORS.
  

  
  


• 
  

  Visit manual>The print Statement:

  
  
  

  
  

  The print Statement

  
  
  

  Use the print statement to produce output with simple, standardized formatting. You specify only the strings or numbers to print, in a list separated by commas. They are output, separated by single spaces, followed by a newline. The statement looks like this:

  
  
  

  print item1, item2, …
  

  
  

  
  

Visit man awk for more details.

Also note that:

PATTERNS AND ACTIONS
 AWK is a line-oriented language. The pattern comes first, and then the action. Action statements are
 enclosed in and . Either the pattern may be missing, or the action may be missing, but, of course, not
 both. If the pattern is missing, the action is executed for every single record of input. A missing action
 is equivalent to

 print 

 which prints the entire record.

awk doesn't have echo keyword/statement.

$ man awk | grep echo | wc -l
0