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Chapter 51 Miscellaneous Useful Programs and Curiosities |
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51.10 The date Command
All UNIX systems come with a program called date . It shows you the time from the system clock ( 51.2 ) . (So, the time is only as accurate as your system's clock.) For example:
%dateFri Dec 13 08:06:39 PST 1996
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date
|
If you need parts of that date, you can split the line into pieces.
There are examples in articles
16.18
,
21.3
,
and
2.5
.
Most newer versions of
date
(including the one on the Power Tools
disc) will also let you set the format of the date.
To do that, type a single argument that starts with a plus (
+
)
and has format specification characters in it.
Check your online manual page for a list of format specification
characters.
The argument has to be all one word, so you'll usually need to put
quotes (
8.14
)
around it.
Here's a simple example: |
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%date +'Today is %d %h 19%y.'Today is 13 Dec 1996.
You'll usually use this in a shell script or
alias (
10.2
)
.
Because
date
can mix any other text with the dates it outputs,
you can do some surprising and useful things.
Greg Ubben uses it to construct arithmetic
expressions for performing calculations on dates.
For example, since
date +%U
isn't available on all systems,
the following computes the week number of the year
(Sunday as the first day) and makes it available in the Bourne shell
as
$weekno
:
expr `...` |
weekno=`expr \`date +"%j / 7 + ( ( %w + 6 ) %% 7 < %j %% 7 )"\`` |
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For some other "real-life" examples, see articles 16.16 , 18.3 , and 21.14 .
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| 51.9 Making a "Login" Shell |
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51.11 Making an Arbitrary-Size File for Testing |
