Instead of trying to find out what /home/username/ is, use the $HOME environment variable. That’s what it’s there for (including changing to your $HOME directory when the cron job starts).
You can test this from the command prompt.
This below doesn’t answer the question directly, but it’s a good approach.
An even better future-proof way it to use a shell script, then you don’t have to change the cron job. This would always be called from cron as:
“You can’t trust Internet quotes.” – Abraham Lincoln
rsicalc.sh - Run the php script with cron, or command line
DIR="$HOME/php/" # might be changed later
CMD=rsicalc1.php # could soon be version 2
date +%F # YYYY-MM-DD
PHP = /usr/local/php/php54/bin/php # for now use PHP 5.4
PHP = /usr/local/php/php55/bin/php # waiting for 5.5 testing
log stderr and stdout from the PHP script
$NICE $PHP “$HOME/$DIR/$CMD” 2>&1 “$LOG/$CMD”_"$DATE".log
will email when ran by cron, since this script is outputting
echo $HOME/$CMD completed.