06-11-2010
Unless you have GNU date there is no simple code to do this. CFA Johnson, a forum member, has a website with a shell script library to do date arithmetic. The code is good, but doing dates in shell in an involved.
Rolling your own date routines is not best practice. Finding yesterday when the date today is March 1 is a classic example. You have to know whether it is a leap year or not, then roll back to Feb 28 or 29.
The standard way to get yesterday:
calculate the current Julian day, subtract one, then convert Julian -> Gregorian date.
get current time in UNIX epoch seconds and subtract 86400, then convert epoch seconds to a Gregorian date.
For production systems always use known good libraries for date calculations.
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script(1) User Commands script(1)
NAME
script - make record of a terminal session
SYNOPSIS
script [-a] [filename]
DESCRIPTION
The script utility makes a record of everything printed on your screen. The record is written to filename. If no file name is given, the
record is saved in the file typescript. See WARNINGS.
The script command forks and creates a sub-shell, according to the value of $SHELL, and records the text from this session. The script ends
when the forked shell exits or when Control-d is typed.
OPTIONS
The following option is supported:
-a Appends the session record to filename, rather than overwriting it.
NOTES
script places everything that appears on the screen in filename, including prompts.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
|CSI |Enabled |
+-----------------------------+-----------------------------+
SEE ALSO
attributes(5)
WARNINGS
script can pose a security risk when used in directories that are writable by other users (for example, /tmp), especially when run by a
privileged user, that is, root. Be sure that typescript is not a link before running script.
SunOS 5.10 30 Jan 2004 script(1)