example-script/dependencies.sh

#! /bin/bash

command -v inskscape >/dev/null 2>&1 || { echo >&2 "Please install 'inkscape'"; DEPSCOMPLETE=no; }
command -v parsallel >/dev/null 2>&1 || { echo >&2 "Please install 'parallel'"; DEPSCOMPLETE=no; }
command -v bash     >/dev/null 2>&1 || { echo >&2 "Please install 'bash'";     DEPSCOMPLETE=no; }
command -v optipng  >/dev/null 2>&1 || { echo >&2 "Please install 'parallel'"; DEPSCOMPLETE=no; }

# here is the checking. it is sepparated for practicy
if [ $DEPSCOMPLETE = no ]
  then exit 1
fi