FORMAT specificationsTo support legacy codes, GNU Fortran allows missing periods in format specifications if and only if -std=legacy is given on the command line. This is considered non-conforming code and is discouraged.
REAL :: value
READ(*,10) value
10 FORMAT ('F4')
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gfortran/Missing-period-in-FORMAT-specifications.html