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# 1  
Old 06-09-2011
fields in AWK

I feel like a real leech now, 3 questions in 3 days, but hopefully when I get my head around all of this I can contribute back to this community!

Anyway, so a couple of you guys have gotten me onto AWK and I've been researching it a little over the last couple of hours, now I'm somewhat sure I know the answer to this question, I'm just chasing confirmation.


In AWK $0 will grab an entire line (record) $1 will grab the first field, $2 grabs the second etc

I'm curious as to what exactly constitutes a field.

Personally I think a field is just 1 character, but part of me thinks that it would be 1 string.

With the following data for example:

Quote:
700k ../acushare.err
Now, printing $0 should print that entire line
What does printing $1 output? 7? or 700k?

Mid way through creating this thread I attempted to test this theory myself, but i couldn't quite use the right command apparrently.

I tried the following:

1.
 
Code:
awk 'BEGIN { print $1 }' data_SAMPLE1_test
output: blank line

2.
Code:
awk 'BEGIN { print $1 }' data_SAMPLE1_test > new111
output: empty file

3.
Code:
awk 'BEGIN { print $0 }' data_SAMPLE1_test > new111
output: empty file

I also tried print by itself with no luck.

Which I guess means I'm asking a new sub-question here, why is my command not working?



So.. long and short of it, an hour or so research and I'm still complete and utter noob!

Any and all help as always is greatly appreciated Smilie

Last edited by Aussiemick; 06-09-2011 at 10:48 PM.. Reason: extra info
# 2  
Old 06-09-2011
By default, a field is a sequence of characters delimited by spaces and tabs. So, everything up to the first tab/space is field 1. Any spaces and tabs following that field are a delimiter. Multiple spaces and tabs in a row do not create empty fields. Also, by default, leading and trailing whitespace are ignored during field splitting.

You can change the delimiter using the -F option or by setting the FS AWK variable.

The reason your code isn't working is because the BEGIN pattern is executed before AWK reads the first line of the file. Remove 'BEGIN' and it should work as you intend.

Should you ever find yourself needing to read lines in a BEGIN pattern, you need to explicitly use getline.

Regards,
Alister
This User Gave Thanks to alister For This Post:
# 3  
Old 06-10-2011
Awesome, yeah I have a space between the file size (700k) and filename (data_sample1_test) on purpose and hoped that each field was infact each string/delimited by spaces.

Also the reason I used BEGIN was because when I was playing with a Hello World script I came across on wikipedia I took out the BEGIN and somehow created an infinite loop where whenever I typed anything, it would be followed by Hello, World! until I forced a stop.


Thanks very much for the reply alister.

---------- Post updated at 12:46 PM ---------- Previous update was at 11:22 AM ----------

I understand what I did to create this infinite loop thing, as I just tried what you said and it happened again.
Was just a silly mistake on my part, and technically I suppose it's not an infinite loop at all, I'm just outputting the result straight to linux (i think)

So it was literally the difference between giving it a file to access from or not giving it a file
Accessing from data_SAMPLE1_test
Code:
awk ' { print $0 }' data_SAMPLE1_test > new111

Not accessing a file
Code:
awk ' { print $0 }' > new111

I know that must seem extremely stupid and/or simple, but I guess I'm so new to this language it didn't occur to me straight away Smilie
 

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