awk command doubt

What is awk?
NF?
FS?
OFS?
$0?
-F?
' '?

NF - number of fields
FS - Field Separator
$0 - refers to the complete line , whereas $1 refers to field 1

how to use awk to locate lines longer than 100 and smaller than 150 characters.......?

awk ' { if (length > 100 && length < 150) print }' filename

I have edited this now.Must be spacing problem.It is working for me!

[335723@oracleclient ~]$ awk '{length 5 && length < 10 ) print }' aaa.txt
awk: {length 5 && length < 10 ) print }
awk: ^ syntax error

help me out...........

Where is the if clause ? And inside if the condition is enclosed in ()

What is the use of BEGIN pattern in awk cmd?
Can any1 explain with an example??

BEGIN block ll be executed once the execution of awk file starts.
END block ll be executed once the exection ends.
Other blocks ll be executed for all ur inputs.

Example

Code:

$ cat sample.awk
BEGIN { print "WELCOME TO UNIX" }
{ print $1 }
END { print "THANK U.. VISIT AGAIN... " }

$ awk -f sample.awk
WELCOME TO UNIX
orange colour
orange
candle light
candle
THANK U.. VISIT AGAIN...


Hey thanks..
understood

Can someone post more examples of awk command usage with explanation?

awk basically reads one line at a time, matches the particular pattern specified.If the match is found, it performs the action on that line!

Eg :- awk '/gold/ {print}' coins.txt

If gold is found in any line of the file 'coins.txt' , then print all lines in coins.txt containing gold.

What does awk -f sample.awk do ?

What is the purpose of -f ?

'-f' means awk program is saved in a separate file and argument followed by -f is the name of the awk script file. multiple -f can also be used.