[ale] Move last line of a file to first line

[Ed Cashin]

Thanks for mentioning the non-stream editor!  They made sed for streams,
because ed is for files.  It is at times like this when I sincerely regret
the way distros are beginning to omit ed for the first time in decades.

There's an ed move command called "m".  Move this line to that line.  The
one liner below does the same thing as this interactive session

$m0
w
q

ecashin at reynolds:~$ head /etc/passwd | nl > ~/tmp/a
ecashin at reynolds:~$ cp ~/tmp/a ~/tmp/b
ecashin at reynolds:~$ printf '$m0\nw\nq\n' | ed ~/tmp/b
414
414
ecashin at reynolds:~$ diff -u ~/tmp/a ~/tmp/b
--- /home/ecashin/tmp/a 2012-03-28 21:40:25.000000000 -0400
+++ /home/ecashin/tmp/b 2012-03-28 21:41:44.000000000 -0400
@@ -1,3 +1,4 @@
+    10 news:x:9:9:news:/var/spool/news:/bin/sh
      1 root:x:0:0:root:/root:/bin/bash
      2 daemon:x:1:1:daemon:/usr/sbin:/bin/sh
      3 bin:x:2:2:bin:/bin:/bin/sh
@@ -7,4 +8,3 @@
      7 man:x:6:12:man:/var/cache/man:/bin/sh
      8 lp:x:7:7:lp:/var/spool/lpd:/bin/sh
      9 mail:x:8:8:mail:/var/mail:/bin/sh
-    10 news:x:9:9:news:/var/spool/news:/bin/sh
ecashin at reynolds:~$

On Wed, Mar 28, 2012 at 12:41 PM, Richard Bronosky <Richard at bronosky.com>wrote:

> Be careful doing this with large files. You are storing the whole file
> in memory.
>
> I would do this in 2 passes.
>
> # First get the last line into a new file. (assuming the file in
> question is passed in as the first argument)
> tail -n1 $1 > $1.mod
> # Second add the rest of the file, less the last line.
> sed '$d' $1 >> $1.mod
>
> This is working with streams. It requires an additional $filesize of
> disk space, but it does not require $filesize of RAM.
>
> If you want to be really efficient, use ed. ;-)
> # This will trim the last line of the file in place, but I'm not
> taking the time to figure out how to add it to the beginning.
> ed "$1" << EOF
> $
> d
> w
> EOF
>
> On Mar 28, 2012 11:19 AM, "Lightner, Jeff" <JLightner at water.com> wrote:
> >
> > I found this works:
> >
> > awk '{a[NR]=$0} END {print a[NR]; for (i=1;i<NR;i++) print a[i]}'
> originalfile >newfile
> >
> >
> >
> > Where you replace originalfile and newfile with real file names.
> >
> >
> >
> >
> >
> >
> >
> > ________________________________
> >
> > From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of
> Lightner, Jeff
> > Sent: Wednesday, March 28, 2012 11:10 AM
> > To: Atlanta Linux Enthusiasts
> > Subject: [ale] Move last line of a file to first line
> >
> >
> >
> > We have variable length text files being received in which the “header”
> line we use in automated processing is the last line of the file rather
> than the first line.
> >
> >
> >
> > What is the best way to move that last line of a text file to be the
> first line?
> >
> >
> >
> > Please answer the question as asked and don’t suggest making the file be
> in the correct order when we receive it or changing the automated
> processing to read the last line first.  Assume those aren’t options.
> >
> >
> >
> > What I came up with was to do tail -1 >newfile and head -<number of
> lines – 1> but was thinking there ought to be a better way.
> >
> >
> >
> > I see sed can deal with last line, first line and insertion but the
> examples I’m finding address either/or not moving last line to first line.
> >
> >
> >
> >
> >
> >
> >
> >
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-- 
  Ed Cashin <ecashin at noserose.net>
  http://noserose.net/e/
  http://www.coraid.com/
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