conditions syntax in bash

condition_syntax_bash.sh

## check the return of a command
if command; then
  [...]
fi

## check by string comparison / numerical  / file existence / or more

if [[ CHECK ]]; then
  [...]
fi

# CHECK can be one of :
# string1 = string2 => string are equals
# string1 != string2 => string are not equals
# val1 -eq val2 => numbers are equals
# val1 -neq val2 => numbers are not equals
# val1 -gt val2 => val1 is greater than val2
# val1 -gte val2 => val1 is greater than or equal to val2
# val1 -lt val2 => val1 is lower than val2
# val1 -lte val2 => val1 is lower than or equal to val2
# etc etc
# all comparator can be found with `man test`