Need explanation of script


 
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Old 11-25-2007
Need explanation of script

Hi
All,


Can anybody explain what this script is doing?

#!/bin/sh
who | cut -d " " -f1 | sort -u > userlist1
while true ; do
sleep 60
who | cut -d" " -f1 | sort -u >userlist2
for username in `cat userlist1` ; do
if ! grep "^$username$" userlist2 > /dev/null ; then
echo "$username has logged out"
fi
done
for username in `cat userlist2` ; do
if ! grep "^$username$" userlist1>/dev/null; then
echo "$username hass logged in"
done
mv userlist2 userlist1;
done

Thanks,
Vishal
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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)

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