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Top Forums UNIX for Dummies Questions & Answers Subtracting Variables which are commands Post 1771 by PxT on Thursday 29th of March 2001 10:55:10 AM
Old 03-29-2001
This gets tricky because what if their login time is 2:59, and the logout time is 3:10. 3:10-2:59=? The shell doesn't know that you are trying to subtract times, it just sees numbers with a colon in the middle. A better way to do this might be to use the 'last' command, as one of the fields it provides is the total log in time.
 

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LOGIN(3)						   BSD Library Functions Manual 						  LOGIN(3)

NAME
login, logout, logwtmp -- login utility functions (DEPRECATED) SYNOPSIS
#include <util.h> void login(struct utmp *ut); int logout(const char *line); void logwtmp(const char *line, const char *name, const char *host); DESCRIPTION
The login(), logout(), and logwtmp() functions are DEPRECATED; use pututxline(3) instead. These functions operate on the database of current users in /var/run/utmpx and the system log file. Superuser permission is required. The login() function updates the /var/run/utmpx files with user information contained in ut (after converting to a struct utmpx, as described in pututxline(3)). The logout() function removes the entry from /var/run/utmpx corresponding to the device line. The logwtmp() function adds an entry to the system log file. Since login() will add the appropriate entry during a login, logwtmp() is usu- ally used for logouts. RETURN VALUES
logout() returns non-zero if it was able to find and delete an entry for line, and zero if there is no entry for line in /var/run/utmpx. However, there is no error indication due to lack of permissions. FILES
/dev/* /var/run/utmpx SEE ALSO
pututxline(3), utmp(5), utmpx(5) BSD
December 14, 1995 BSD
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