##########################################################################
# Shellscript:	homework - execute command in all HOME directories
# Author     :	Heiner Steven <heiner.steven@odn.de>
# Date       :	1993-02-23
# Category   :	System Administration
# SCCS-Id.   :	@(#) homework	1.3 04/02/18
##########################################################################
# Description:
#    -	Reads user names from standard input, changes into their HOME
#	directory, and executes the given command
#    -	The command can use the environment variables
#	    H_USER	current user name
#	    H_HOME	current home directory
##########################################################################

PN=`basename "$0"`		# Program name
VER='1.3'			# Version number

: ${GREP:=grep}
: ${TMPDIR:=/tmp}		# Directory with temporary files

UserFile=$TMPDIR/ho$$.1		# Names of the users
EtcFile=$TMPDIR/ho$$.2		# Names and home directories of users
All=false			# Process all, or specified users

Usage () {
    echo >&2 "$PN - execute command in all HOME directories, $VER
usage: $PN [-a] command [arg ...]
    -a:  process HOME directories of all users

The given command will be executed with the arguments specified in the
home directory of users.

The called program can use the environment variables H_USER and H_HOME
containing the current user name and the current home directory name.
    
The user names are read from standard input. Only the first word of each
line will be used, the rest of the line will be ignored.

Examples:
    who | $PN pwd
    $PN cleanup < userlist"
    exit 1
}

#
# MAIN PROGRAM
#

if [ $# -lt 1 ]
then
    Usage
else
    case "$1" in
	-a)	All=true			# alle User bearbeiten?
		shift ;;
	-*)	Usage ;;		# unbekanntes Flag
    esac
fi

# Is standard input redirected?
if [ -t 0 ]
then isatty=true
else isatty=false
fi

# Remove temporary files after receiving an interrupt
trap "rm -f $EtcFile $UserFile" 0
trap "echo \"$PN: Interrupt; Abbruch!\"; exit 1" 1 2 3 15

# Write user name and home directory separated by a TAB character into
# temporary file

#(cat /etc/passwd; ypcat passwd 2>/dev/null) |
getent passwd |
    cut -d':' -f1,6 |			# user name and home directory
    sed -e 's/:/	/g' > "$EtcFile" || {
	echo "$PN: could not create user/directory list: $EtcFile"
	exit 1
    }

# Save user list

> "$UserFile" || {
    echo >&2 "$PN: cannot create user list file: $UserFile"
    exit 1
}

if [ "$All" = true ]
then
    # Read all users
    cut -d':' -f1 < "$EtcFile" >> "$UserFile" || {
	echo "$PN: could not create user list from passwd file"
	exit 1
    }
else
    # Print short message if we read from keyboard
    [ "$isatty" = true ] && \
    	echo >&2 "[$PN: enter user names: one name per line, ^D to terminates]"

    while read UserName Rest
    do
	test -z "$UserName" && continue	# Ignore empty lines

	# Is this a valid user name?
	"$GREP" "^$UserName	" "$EtcFile" > /dev/null || {
	    echo >&2 "$PN: cannot find user '$UserName'; ignored."
	    continue
	}
	echo "$UserName" >> "$UserFile"
    done
fi

# Ensure that interactive programs always read from the current
# standard input, even if stdin is a file/pipe. In these cases,
# standard input will be redirected to /dev/tty for the time
# the command is executed.
#
# File descriptors:
#   3 - keyboard
#   4 - $EtcFile

# Note: descriptor 0 gets lost reading from /dev/tty

if [ "$isatty" = true ]
then exec 3<&0 4<"$EtcFile" 0<&4
else exec 3</dev/tty 4<"$EtcFile" 0<&4
fi

echo >&2 "$PN: start `date`"

# Main loop: execute command in home directory

Oldwd=`pwd`
while read Name HomeDir Rest
do
    "$GREP" "$Name" "$UserFile" > /dev/null || continue	# ignore

    [ -n "$HomeDir" -a -d "$HomeDir" ] || {
	echo >&2 "$PN: user '$Name' has no valid home directory: $HomeDir"
	continue
    }

    [ -r "$HomeDir" -a -x "$HomeDir" ] || {
	echo >&2 "$PN: need read and execute permissions: $HomeDir"
	continue
    }

    cd "$HomeDir"			# cannot fail...

    echo >&2 "$PN: processing: $Name ($HomeDir)"
    H_USER="$Name"	export H_USER
    H_HOME="$HomeDir"	export H_HOME

    # Interactive programs: always read from keyboard
    exec 0<&3
    ${SHELL:-/bin/sh} -c "$@"
    exec 0<&4

    cd "$Oldwd"
done

exec 0<&3 3<&- 4<&-

echo >&2 "$PN: end `date`"