is a shell script, not a program written in GFortran.
comparison operator means "not equal to". The semicolon after the closing bracket is part of the syntax for an if
statement in most shells:
if [ condition ]; then statement(s) ; fi
shell variable contains the exit code for the last command/executable that was run. An exit code of 0 indicates that the program/command completed without errors. In other words, the if
statement seems to say: "if the previous program encountered an error and returned a non-zero exit code, do [whatever comes after then