A format specification can also include modifiers that can control how much of the item's value is printed and how much space it gets. The modifiers come between the `%' and the format-control letter. In the examples below, we use the bullet symbol "*" to represent spaces in the output. Here are the possible modifiers, in the order in which they may appear:
printf "%-4s", "foo"prints `foo*'.
printf "%4s", "foo"prints `*foo'. The value of width is a minimum width, not a maximum. If the item value requires more than width characters, it can be as wide as necessary. Thus,
printf "%4s", "foobar"prints `foobar'. Preceding the width with a minus sign causes the output to be padded with spaces on the right, instead of on the left.
printf "%.4s", "foobar"prints `foob'.
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, you pass them 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
Both programs output `**abc'.
Earlier versions of
awk did not support this capability.
If you must use such a version, you may simulate this feature by using
concatenation to build up the format string, like so:
w = 5 p = 3 s = "abcdefg" printf "%" w "." p "s\n", s
This is not particularly easy to read, but it does work.
C programmers may be used to supplying additional `l' and `h'
printf format strings. These are not valid in
awk implementations silently ignore these flags.
If `--lint' is provided on the command line
(see section Command Line Options),
gawk will warn about their use. If `--posix' is supplied,
their use is a fatal error.
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