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From: Hongyi Zhao on 26 Nov 2009 00:46
On Wed, 25 Nov 2009 22:41:04 -0600, Ed Morton <mortonspam(a)gmail.com>
wrote:

>OK, so you don't actually want to swap anything, you want to find "line_b" and
>move it to earlier in the file, specifically right after "line_a", right? try this:
>
>tac file | awk '/line_b/{b=$0 RS; next} /line_a/{printf "%s",b} 1' | tac

Let me give a minimal example:

$ cat test_swap2lines.txt
some_others1
line_b
some_others2
line_a
some_others3

I want to obtain the following result:

some_others1
some_others2
line_a
line_b
some_others3

But, your above code will give something like this:

$ tac test_swap2lines.txt | awk '/line_b/{b=$0 RS; next}
/line_a/{printf "%s",b
} 1' | tac
some_others1
some_others2
line_a
some_others3

In the result given by your code, the line_b is removed from the
result, which is not the result I want.

Best regards.
--
..: Hongyi Zhao [ hongyi.zhao AT gmail.com ] Free as in Freedom :.
From: w_a_x_man on 26 Nov 2009 04:47
On Nov 25, 11:46 pm, Hongyi Zhao <hongyi.z...(a)gmail.com> wrote:
> On Wed, 25 Nov 2009 22:41:04 -0600, Ed Morton <mortons...(a)gmail.com>
> wrote:
>
> >OK, so you don't actually want to swap anything, you want to find "line_b" and
> >move it to earlier in the file, specifically right after "line_a", right? try this:
>
> >tac file | awk '/line_b/{b=$0 RS; next} /line_a/{printf "%s",b} 1' | tac
>
> Let me give a minimal example:
>
> $ cat test_swap2lines.txt
> some_others1
> line_b
> some_others2
> line_a
> some_others3
>
> I want to obtain the following result:
>
> some_others1
> some_others2
> line_a
> line_b
> some_others3
>
> But, your above code will give something like this:
>
> $ tac test_swap2lines.txt | awk '/line_b/{b=$0 RS; next}
> /line_a/{printf "%s",b} 1' | tac
>
> some_others1
> some_others2
> line_a
> some_others3
>
> In the result given by your code, the line_b is removed from the
> result, which is not the result I want.

Using Ruby:

# Read the file.
gets(nil)
# Remove Line B.
sub!( /.*line_b.*\n/, "" )
# Remember Line B.
b = $&
# Insert Line B after Line A.
puts sub( /line_a.*\n/, '\&' + b )
From: Hongyi Zhao on 26 Nov 2009 07:25
On Thu, 26 Nov 2009 01:47:17 -0800 (PST), w_a_x_man
<w_a_x_man(a)yahoo.com> wrote:

>Using Ruby:
>
># Read the file.
>gets(nil)
># Remove Line B.
>sub!( /.*line_b.*\n/, "" )
># Remember Line B.
>b = $&
># Insert Line B after Line A.
>puts sub( /line_a.*\n/, '\&' + b )

Very good, thanks a lot, you let me know a succinct and powerful tool.

Best regards.
--
..: Hongyi Zhao [ hongyi.zhao AT gmail.com ] Free as in Freedom :.
From: Hongyi Zhao on 26 Nov 2009 07:37
On Thu, 26 Nov 2009 01:47:17 -0800 (PST), w_a_x_man
<w_a_x_man(a)yahoo.com> wrote:

>Using Ruby:
>
># Read the file.
>gets(nil)
># Remove Line B.
>sub!( /.*line_b.*\n/, "" )
># Remember Line B.
>b = $&
># Insert Line B after Line A.
>puts sub( /line_a.*\n/, '\&' + b )

Is it possible to edit the input file in place by uisng ruby, i.e.,
just like the -i OPTION for sed?

Best regards.
--
..: Hongyi Zhao [ hongyi.zhao AT gmail.com ] Free as in Freedom :.
From: w_a_x_man on 26 Nov 2009 16:37
On Nov 26, 6:37 am, Hongyi Zhao <hongyi.z...(a)gmail.com> wrote:
> On Thu, 26 Nov 2009 01:47:17 -0800 (PST), w_a_x_man
>
> <w_a_x_...(a)yahoo.com> wrote:
> >Using Ruby:
>
> ># Read the file.
> >gets(nil)
> ># Remove Line B.
> >sub!( /.*line_b.*\n/, "" )
> ># Remember Line B.
> >b = $&
> ># Insert Line B after Line A.
> >puts sub( /line_a.*\n/, '\&' + b )
>
> Is it possible to edit the input file in place by uisng ruby, i.e.,
> just like the -i OPTION for sed?

Yes.
ruby -i.bak -pe'gsub( "c", "x" )' data

This makes a backup file named "data.bak" and replaces
each "c" with "x".

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