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Shell Programming and Scripting

Script to move the first line of a file to the end

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Top Forums Shell Programming and Scripting Script to move the first line of a file to the end
# 15  
Old 12-31-2008
Quote:
Originally Posted by methyl
It is possible to write scripts which might work efficiently but are unintelligible to newbies. The previous post with "IFS" is a classic.

That line is the only way to guarantee reading an entire line. No one but a total newbie should have any problem with it.

There used to be a line command that did the same thing, but that is rarely found these days.
# 16  
Old 12-31-2008
Quote:
Originally Posted by cfajohnson
That line is the only way to guarantee reading an entire line. No one but a total newbie should have any problem with it.
I have to agree. I any case to know the purpose of, and have some concept of the effect of the manipulation of IFS is something that a new scripter would be well advised to learn. It can make some tasks truly trivial.
# 17  
Old 01-01-2009
When manipulating records with shell it is good practice to never put the record into a shell variable. We've had examples on this board where the data has changed because the record contained characters recognised by the shell (e.g. reverse solidus).
Obviously with known valid data there is no problem.
# 18  
Old 01-02-2009
sed -n '1 {
h
}
1 !{
$ !{
p
}
$ {
p
x
p
}
}' a.txt
# 19  
Old 01-02-2009
Hi.

Useful for small files, the simple editor, ed, has a move command:
Code:
#!/bin/bash -

# @(#) s1       Demonstrate editing file in place with script-able line editor, ed.

echo
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1) ed
set -o nounset
echo

FILE=${1-data1}

cp original $FILE
echo " Data file $FILE:"
cat $FILE

echo
echo " Messages from ed:"
ed $FILE <<EOF
1m$
w
q
EOF

echo
echo " Modified data file $FILE:"
cat $FILE

exit 0

Producing:
Code:
% ./s1

(Versions displayed with local utility "version")
Linux 2.6.11-x1
GNU bash
GNU ed version 0.2

 Data file data1:
/home/user/Music/file1.mp3
/home/user/Music/file2.mp3
/home/user/Music/file3.mp3
/home/user/Music/file5.txt
/home/user/Music/file7.wav
/home/user/Music/file11.ogg
/home/user/Music/file13.m4a

 Messages from ed:
191
191

 Modified data file data1:
/home/user/Music/file2.mp3
/home/user/Music/file3.mp3
/home/user/Music/file5.txt
/home/user/Music/file7.wav
/home/user/Music/file11.ogg
/home/user/Music/file13.m4a
/home/user/Music/file1.mp3

See man ed for details on the editing commands ... cheers, drl
# 20  
Old 01-07-2009
move command will do
eg : a.txt
a
b
c
d
e
f

execute this script :


vi - a.txt <<END
:mv 1 $
:x
<<END
# 21  
Old 01-07-2009
Hi, palanisvr.

Even after correcting the here document from:
Quote:
Originally Posted by palanisvr
vi - a.txt <<END
:mv 1 $
:x
<<END
to:
Quote:
Originally Posted by palanisvr
vi - a.txt <<END
:mv 1 $
:x
END
I cannot get your script to work correctly with the vi that I use. Please post all the the output from your script, and please use CODE tags to enhance readability. Thanks ... cheers, drl
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