Question

I’m trying to rename several different files in bash.
How to rename for example temp_1 to temp_01 until 09 (temp_9 to temp_09)?

I used sed but somehow didn’t work.

I tried with this:

 for i in temp_?.txt; 
 do
   j=echo $i | sed 's/[^0-9]*/0[^0-9]*/g';
   mv "$i" "$j"; 
 done 

Answer 1

Try to modify your sed command to something like

sed 's/[0-9]/0&/'

That will do the work for your example case.

Your command doesn’t work because when you are trying to reference the matched string you actually don’t: it’s done with & (for the whole match) or numbered references.