Question

I want to insert 4 blanks in a text named test.

sed 's/^/  \{4\}/'  test  

Why it can’t work?how can i do?

how about i want to add 10 blanks or 20 blanks?

sed 's/^/    /' test  #can work ,but not well done

Answer 1

nneonneo explained why your script didn’t work. It is fairly well known how to pad lines on the left with spaces to achieve lines of a fixed width, but adding the same number of blanks to the left a line for every line in sed is a different problem.

If you can bear to use something other than sed,

Or you can use ruby

ruby -e 'ARGF.each {|l| puts (" " * 4) + l}' test

Or you can use awk:

awk '{for (i=0; i<4; i++) printf(" "); print $0}' test

Or perl:

perl -ne 'printf "%s%s", (" " x 4), $_' test

EDIT: I would like to see a pure sed solution. Using the conditional branch (t) seems useful for padding, but not to do what you ask.