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

[Richard Bronosky]

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:
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> I found this works:
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> awk '{a[NR]=$0} END {print a[NR]; for (i=1;i<NR;i++) print a[i]}' originalfile >newfile
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> Where you replace originalfile and newfile with real file names.
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> ________________________________
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> 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.
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> What is the best way to move that last line of a text file to be the first line?
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> 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.
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> 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.
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> 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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