how can I use sed to replace the lists that begins with (*) in a file

Question

Using sed how can I replace the lines that start with a star and replace it with numbers starting from 1?

I need to replace the (*) in the fist of a list with numbers using sed for example >

this file contain a list

*linux

*computers

*labs

*questions

to >>>>

this file contain a list

1 linux
2 computers
3 labs
4 questions

I tried using

sed -e 's/*//' file.in > file.out | sed -i = file.out

Answer 1

You can use awk:

awk '/^\*/ {sub(/\*/, ++i)} 1' <<END
A list
* one
* two
Blah
* three
END

A list
1 one
2 two
Blah
3 three

Answer 2

You can play some trick - first number lines with * only then strip * and spaces if you want

nl -bp^[*] file | sed 's/^\s*\|\s*\*//g'

Answer 3

{   tr -s \\n |
    sed =|
    sed '$!N;s/\n./ /'
} <<\INPUT
*linux

*computers

*labs

*questions
INPUT

OUTPUT

1 linux
2 computers
3 labs
4 questions

nl is the most obvious, but sed can count lines. sed is not alone in that respect:

sh <<HD
$(sed -n 's/^\*\(.*\)/echo "$LINENO \1"/p' <infile)
HD

...or...

sed -n "s/..*/OUT='&'/p" <infile | 
PS1='${LINENO#0} ${OUT#?}${IFS#??}' dash -i

...both of which print the same as before (even if it is a little silly). I use dash here explicitly because, by default, it does not enable any readline like terminal reader. If dash is your sh you can just use sh, but if bash is linked in to sh you'll need to use the --noediting for the second example to avoid it printing the OUT=... stuff to the terminal as well.

And really, for your simple example case, the entire thing can be done with nl and tr:

tr -d \* <<\INPUT| nl -s ' ' -w1 -nln
*linux

*computers

*labs

*questions
INPUT

OUTPUT

1 linux

2 computers

3 labs

4 questions

Answer 4

I would use perl instead. The syntax for this is very simlar to sed's:

perl -pe 's/^\*/$c++/e' file

Or, to start from 1:

perl -pe 's/^\*/++$c/e' file

And to edit the original file in place:

perl -i -pe 's/^\*/++$c/e' file

Answer 5

I can't come up with a solution that uses only sed, but this comes close. It uses only sed, shell builtins, and cmp and mv. With some effort and a modern shell, you could rewrite this to hold the file contents in shell variables, and not have to use cmp or mv.

#!/bin/sh
if test $# -ne 1
then
    echo usage: $0 file
    exit 1
fi
num=1    # start numbering at 1
infile="$1"
outfile="$1.out"
mv "$infile" "$outfile"    # set up so initial cmp always fails
while ! cmp -s "$infile" "$outfile" # repeat the sed until no more ^* can be found
do
    mv "$outfile" "$infile"
    # replace the first occurrence of ^* with a number and a space
    sed '0,/^\*/s//'$num' /' "$infile" > "$outfile" 
    num=$(expr $num + 1)
done
rm "$outfile"

test:

$ cat i
first line
*second
*third
fourth
*fifth
$ ./change i
$ cat i
first line
1 second
2 third
fourth
3 fifth

Answer 6

sed cannot do calculations thus this is not possible in a useful way.