REQUIREMENTS

cat - concatenate files and print on the standard output
chmod - change file mode bits
du - estimate file space usage
echo - display a line of text
find - search for files in a directory hierarchy
git - the stupid content tracker
grep, egrep, fgrep, rgrep - print lines matching a pattern 
gzip, gunzip, zcat - compress or expand files
join - join lines of two files on a common field
ln - make links between files
mkdir - make directories
mv - move (rename) files
ssh - OpenSSH SSH client (remote login program)
printf - display text according to a format string
pv - monitor the progress of data through a pipe
read - read line of input into variables
rm - remove files or directories
scp - secure copy (remote file copy program)
sed - stream editor for filtering and transforming text
sleep - delay for a specified amount of time
ssh-keygen - authentication key generation, management and conversion
sshpass - noninteractive ssh password provider
tr - translate or delete characters

OPTIONAL
systemd, init - systemd system and service manager OR cron - daemon to execute scheduled commands (Vixie Cron)
php - PHP Command Line Interface 'CLI'