Adding # to the first line

[leblinux]

Dears,

Does sed or other command edit the 1st line and comments it? Meaning adds "#" to the first line in a file for example?

Summary: Insert # to the first line.

Before: Comment me please.
sed command or another command

After: #Comment me please.

------And if possible a way to remove the "#" using command line.

Thanks.

[Irithori]

sed  '1s/\(.*\)/#\1/' <FILE>

Deleting the # is left as a exercise

[leblinux]

sed  '1s/\(.*\)/#\1/' <FILE>

Deleting the # is left as a exercise

it throws the correct output but doesn't save the file.

[Irithori]

If you verified the output, then use the -i flag.
sed will then edit in-place.

[marion50]

Dears,

Does sed or other command edit the 1st line and comments it? Meaning adds "#" to the first line in a file for example?

Summary: Insert # to the first line.

Before: Comment me please.
sed command or another command

After: #Comment me please.

------And if possible a way to remove the "#" using command line.

Thanks.

To insert as asked do

sed -i "1s/^/#/" FILE

where 1 is the 1st line and ^ is the first character of line

To remove the first # of the 1st line do

sed -i "1s/#//" FILE

[Irithori]

That is faster and simpler. Nice

Nitpicker: The remove expression should check for the start of the line, aka: "1s/^#//"
Or better yet: optional tabs/whitespaces before the # : "1s/^\([ \t]\)*#//"