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sed in a for loop

 
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# 1  
Old 06-30-2007
sed in a for loop
dear guys,
I want to replace the beginning of some lines in a file by (,)
The sequence number of lines is located in a file named numbers
so, i used this simple script to do so, but it didn't work. it does'nt recognize the $j in the command sed

#! /bin/sh
for j in `cat numbers`
do
sed '$j s/^/,/' file
done

so what's wrong?!
thanks
# 2  
Old 06-30-2007
should be something like,

Code:
sed ''$var's/^/,/' filename

# 3  
Old 06-30-2007
with awk it would be like,

Code:
lineno=1
awk -v var=$line 'NR == var { $0 = ","$0; print; exit }' filename

Last edited by matrixmadhan; 06-30-2007 at 02:00 PM.. Reason: req forgot !
# 4  
Old 06-30-2007
thanks Matrixmadhan, i tried your first suggession, and it works, but the output is not what i want.
for example: if the for loop run 4 times, then output will display the file 4 times on the screen, every time with only one modification on a certain line.
what i want is that the output is displayed only 1 time with the 4 modifications done on it.
I hope i made my point clear.
also, I want to know the difference between $j and $var.
Thanks alot again
# 5  
Old 06-30-2007
to have one final copy...

you need to replace as and when sed performs the transformation..

it would be something like..

Code:
sed <code> filename > filename.temp
mv filename.temp filename

and at the end
file with name as <filename> will have all the modifications

There is no difference in using $var and $j. They are variables ( variable names ) you can use them as you wish to.
# 6  
Old 06-30-2007
it works
thanks for your usfull hints.
marwan
# 7  
Old 06-30-2007
Hi.

Here is a method to efficiently run sed on the data file only once. It uses sed to create a sed script file that can then be used in a single pass over the data file.

For small files, this will not make much difference, but with large data files, you will save all but one (or two) executions of sed, where n is the number of lines you are changing:
Code:
#!/bin/sh

# @(#) s1       Demonstrate creation of sed script for single-pass.

set -o nounset
echo " sh version: $BASH_VERSION" >&2

# Create the line number test file, can be in any order.

cat >numbers <<EOF
4
7
3
EOF

# Create the test data file.

cat >data1 <<EOF
one
two
three
four
five
six
seven
eight
nine
ten
EOF

# Create the sed script file with sed, for example:
# make
# 44
# into
# 44s/^/,/

sed 's|$|s/^/,/|' numbers >script

# Now efficiently run sed once instead of n times, display the
# data.

sed -f script data1

exit 0

which produces:
Code:
% ./s1
 sh version: 2.05b.0(1)-release
one
two
,three
,four
five
six
,seven
eight
nine
ten

cheers, drl
 
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