Path: utzoo!attcan!uunet!snorkelwacker!mit-eddie!uw-beaver!sumax!thebes!happym!irv
From: irv@happym.wa.com (Irving Wolfe)
Newsgroups: comp.unix.questions
Subject: Re: -F option for awk
Keywords: awk field-separator
Message-ID: <195@happym.wa.com>
Date: 15 Aug 90 13:57:33 GMT
References: <491@llnl.LLNL.GOV>
Organization: Happy Man Corp., Seattle
Lines: 40

In <491@llnl.LLNL.GOV> rjshaw@ramius.ocf.llnl.gov (Robert Shaw) writes:

>print; or print $0; don't do the right thing because the lines come
>out with spaces as the field separators instead of the character given
>to the -F option.


If you change any field, $1 to $NF, then print or print $0 re-composes $0 from
all the individual fields, stringing them together with the output separator
OFS which defaults to space unless you change it.  If you don't touch any
fields, awk should just print the originally input $0.

Thus 
awk -F: '/^i/' /etc/passwd
(here) produces
irv:-------------:101:1:0000-Irving Wolfe(0000):/u/irv:/bin/gsh
 and
awk     '/^i/' /etc/passwd
produces
irv:-------------:101:1:0000-Irving Wolfe(0000):/u/irv:/bin/gsh
exactly the same thing.

Both print the /etc/passwd lines that begin with i exactly as is.

But
awk -F: '/^i/ {$2 = "hoho"; print}' /etc/passwd
produces:
irv hoho 101 1 0000-Irving Wolfe(0000) /u/irv /bin/gsh
It will replace all the :s with spaces.

You need
awk -F: 'BEGIN {OFS = FS} /^i/ {$2 = "hoho"; print}' /etc/passwd
which produces
irv:hoho:101:1:0000-Irving Wolfe(0000):/u/irv:/bin/gsh

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