define awk -F... please

[mary talpas]

I see from the lesson that we use edquota -p gimli 'awk -F': $3 > 499(print$1)' /etc/passwd' to change others users quotas to match gimli but can some explain this part of the command:
'awk -F': $3 > 499(print$1)' /etc/passwd'

thanks.
mary

[marcromansky]

awk is a program within the linux operating system.
essentially here, awk reads the file /etc/password, takes every third column entry that is greater than 499 (-F: $3 > 499 in the script) and prints the 1st column

what it is doing is printing a list of usernames (1st column in /etc/passwd) with UIDs(column 3) greater than 499

[quote="mary talpas"]I see from the lesson that we use edquota -p gimli 'awk -F': $3 > 499(print$1)' /etc/passwd' to change others users quotas to match gimli but can some explain this part of the command:
'awk -F': $3 > 499(print$1)' /etc/passwd'

thanks.
mary[/quote]

[Jonathan Simms]

Hi Mary,

awk, as it is generically called, is a scripting language developed by Aho, Weinberger, and Kernighan.

awk -F: '$3 > 499' '{ print $1 }' /etc/passwd

-F: is telling awk to use the colon character as a field delimiter.

'$3 > 499' This is essentially saying take the third field and see if it's greater than 499. It is using the colon character for parsing here. Looking at /etc/passwd we can see that the field we wish to use in this evaluation is the third one over, which is the UID or user id. The UID field being the third field is $3.

Accordingly $0 would print the whole line, $1 prints the username, $2 the x for passwd, $3 UID etc.

'{ print $1 }' is saying if there are UIDs greater than 499 print the first field, which is $1, which is the username.

/etc/passwd is the file we are examining.

Hope that helps.

Jonathan

[Jonathan Simms]

Haha Marc you got it first. I took too long writing.

[mary talpas]

THANK YOU

[marcromansky]

I conveniently ditched the delimitter piece so I could get it in faster!

[quote="Jonathan Simms"]Haha Marc you got it first. I took too long writing.[/quote]