Using variables in printf format

Question

Suppose I have a file like this:

$ cat a
hello this is a sentence
and this is another one

And I want to print the first two columns with so

Answer 1

If you use * in your format string, it gets a number from the arguments

awk '{printf "%*-s%s\n", 17, $1, $2}' file
hello            this
and              this

awk '{printf "%*-s%s\n", 7, $1, $2}' file
hello  this
and    this

---

As read in The GNU Awk User’s Guide #5.5.3 Modifiers for printf Formats:

The C library printf’s dynamic width and prec capability (for example, "%*.*s") is supported. Instead of supplying explicit width and/or prec values in the format string, they are passed in the argument list. For example:

w = 5
p = 3
s = "abcdefg"
printf "%*.*s\n", w, p, s

is exactly equivalent to:

s = "abcdefg"
printf "%5.3s\n", s