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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CUT-DIFF(1)							  Cutter's manual						       CUT-DIFF(1)

NAME
cut-diff - show difference between 2 files with color SYNOPSIS
cut-diff [option ...] file1 file2 DESCRIPTION
cut-diff is a diff command that uses diff feature in Cutter. It shows difference with color. It's recommended that you use a normal diff(1) when you want to use with patch(1) or you don't need color. OPTIONS
--version cut-diff shows its own version and exits. -c [yes|true|no|false|auto], --color=[yes|true|no|false|auto] If 'yes' or 'true' is specified, cut-diff uses colorized output by escape sequence. If 'no' or 'false' is specified, cut-diff never use colorized output. If 'auto' or the option is omitted, cut-diff uses colorized output if available. The default is auto. -u, --unified cut-diff uses unified diff format. --context-lines=LINES Shows diff context around LINES. All lines are shown by default. When unified diff format is used, 3 lines are shown by default. --label=LABEL, -L=LABEL Uses LABEL as a header label. The first--label option value is used as file1's label and the second --label option value is used asfile2's label. Labels are the same as file names by default. EXIT STATUS
The exit status is 0 for success, non-0 otherwise. TODO: 0 for non-difference, 1 for difference and non-0 for errors. EXAMPLE
In the following example, cut-diff shows difference between file1 and file2: % cut-diff file1 file2 In the following example, cut-diff shows difference between file1 and file2 with unified diff format: % cut-diff -u file1 file2 SEE ALSO
diff(1) Cutter February 2011 CUT-DIFF(1)