bash, echo redirection not to the last line but first

Xeratul · 09-03-2012, 01:37 AM

Hi,

What would be an elegant method to add $var to the beginning of a file?

for instance one does to add a line:
echo $var >> file.txt

echo $var >> file.txt <-- elegant but here at beginning?
so that it reads:
$var

thanks

konsolebox · 09-03-2012, 01:56 AM

Using sed:

Code:

sed -i "1i $var" file

Not sure if it would work regardless of the variable's contents. Haven't tested it much yet. 'sed 1s' works as well but it's less easy.

David the H. · 09-03-2012, 02:05 AM

You can't use redirections for this. Not directly, at least.

sed is one way. But ed is another good choice, as it's a proper text editor.

Code:

var='new stuff to insert'

printf '%s\n' '0i' "$var" '.' 'w' | ed -s file

How to use ed:
http://wiki.bash-hackers.org/howto/edit-ed
http://snap.nlc.dcccd.edu/learn/nlc/ed.html
(also read the info page)

The other option is to do something like this:

Code:

echo "$var" > newfile
cat oldfile >> newfile
mv newfile oldfile