coreutils: Padding and other flags
21.1.4 Padding and other flags
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Unless otherwise specified, ‘date’ normally pads numeric fields with
zeros, so that, for example, numeric months are always output as two
digits. Seconds since the epoch are not padded, though, since there is
no natural width for them.
The following optional flags can appear after the ‘%’:
‘-’
(hyphen) Do not pad the field; useful if the output is intended for
human consumption. This is a GNU extension.
‘_’
(underscore) Pad with spaces; useful if you need a fixed number of
characters in the output, but zeros are too distracting. This is a
GNU extension.
‘0’
(zero) Pad with zeros even if the conversion specifier would
normally pad with spaces.
‘+’
Pad with zeros, like ‘0’. In addition, precede any year number
with ‘+’ if it exceeds 9999 or if its field width exceeds 4;
similarly, precede any century number with ‘+’ if it exceeds 99 or
if its field width exceeds 2. This supports ISO 8601 formats for
dates far in the future; for example, the command ‘date
--date=12019-02-25 +%+13F’ outputs the string ‘+012019-02-25’.
‘^’
Use upper case characters if possible. This is a GNU extension.
‘#’
Use opposite case characters if possible. A field that is normally
upper case becomes lower case, and vice versa. This is a GNU
extension.
Here are some examples of padding:
date +%d/%m -d "Feb 1"
⇒ 01/02
date +%-d/%-m -d "Feb 1"
⇒ 1/2
date +%_d/%_m -d "Feb 1"
⇒ 1/ 2
You can optionally specify the field width (after any flag, if
present) as a decimal number. If the natural size of the output of the
field has less than the specified number of characters, the result is
written right adjusted and padded to the given size. For example, ‘%9B’
prints the right adjusted month name in a field of width 9.
An optional modifier can follow the optional flag and width
specification. The modifiers are:
‘E’
Use the locale’s alternate representation for date and time. This
modifier applies to the ‘%c’, ‘%C’, ‘%x’, ‘%X’, ‘%y’ and ‘%Y’
conversion specifiers. In a Japanese locale, for example, ‘%Ex’
might yield a date format based on the Japanese Emperors’ reigns.
‘O’
Use the locale’s alternate numeric symbols for numbers. This
modifier applies only to numeric conversion specifiers.
If the format supports the modifier but no alternate representation
is available, it is ignored.
POSIX specifies the behavior of flags and field widths only for ‘%C’,
‘%F’, ‘%G’, and ‘%Y’ (all without modifiers), and requires a flag to be
present if and only if a field width is also present. Other
combinations of flags, field widths and modifiers are GNU extensions.