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%token STRING %token RIGHT_APPEND %% cmd: fg_cmd | bg_cmd ; bg_cmd: fg_cmd '&' ; fg_cmd: simple_cmd | pipe_cmd ; simple_cmd: /* empty command */ | executable | executable input_redirection | input_redirection executable | executable output_redirection | output_redirection executable | executable input_redirection output_redirection | input_redirection executable output_redirection | input_redirection output_redirection executable | executable output_redirection input_redirection | output_redirection executable input_redirection | output_redirection input_redirection executable ; executable: STRING | STRING executable; input_redirection: '<' STRING; output_redirection: overwrite_output_redirection | append_output_redirection ; overwrite_output_redirection: '>' STRING ; append_output_redirection: RIGHT_APPEND STRING ; pipe_cmd: left_cmd '|' right_cmd | left_cmd '|' middle_cmd right_cmd ; left_cmd: executable | executable input_redirection | input_redirection executable ; middle_cmd: executable '|' | middle_cmd executable '|' ; right_cmd: executable | executable output_redirection | output_redirection executable ; %% int main(int argc, char *argv[]) { yyparse(); return 0; } int yywrap() { return 1; } int yyerror(char *msg) { printf("Error encountered: %s\n", msg); }