Shell Programming and Scripting

Look at the difference here, we use usually to make code simple

Code:

$ echo "My test row" | awk '{$1=$2 OFS $1}1'
test My test row

Code:

$ echo "My test row" | awk '{$1=$2 OFS $1;print}'
test My test row

I guess using '1' makes the program more cryptic rather than making it simple. To conserve space, programmers normally use '1' instead of print.

In awk the default action if a condition is true is to print record.

So you can use any number other than 0 to print record, this is because 0 represents false and non-zero represents true.

Code:

awk 1 filename # will print records in file
awk 5 filename # will print records in file
awk 0 filename # will not print records in file

To further explain what Akshay Hegde said, an awk program consists of pairs of the following form:

Code:

pattern { action }

If the given pattern evaluates to a non-zero value for the current input line, the statements included in the action are executed for that line. If pattern is missing, the statements in action will be performed for every input line.
If a pattern is specified and there is no { action }, the action defaults to print (which is shorthand for print $0) which prints the current line.

So, the program:

Code:

{$f = w OFS $f}1

which is equivalent to:

Code:

{$f = w OFS $f}
1

contains two pairs. The first has no pattern and sets the field named by f to the given word followed by the output field separator followed by the original contents of that field. The second pair has no action and since 1 is non-zero, prints the (modified) current line.

thanks everyone

---------- Post updated at 03:57 PM ---------- Previous update was at 03:54 PM ----------

one more query; like if we need to mentioned print then we need to mentioned inside the bracket and if we need to use 1 the out of bracket is it

Code:

echo "My test row" | awk '{$1=$2 OFS $1}1'

The 1 here replace
1 {print $0}
You can also remove the 1 since no pattern gives true and just do:
{print $0}
or
{print}

and since expression before also does not have any pattern, just the code {code}, we can put the print there too since its always true.
{$1=$2 OFS $1;print}

Do study some tutorial for awk and you will see how it works.