Add leading 0 in sed substitution

Question

I have input data:

foo 24
foobar 5 bar
bar foo 125

and I\'d like to have output:

foo 024
foobar 005 bar
bar foo 125
         


        

Answer 1

Add the max number of leading zeros first, then take this number of characters from the end:

echo 55 | sed -e 's:^:0000000:' -e 's:0\+\(.\{8\}\)$:\1:'

00000055