psql: Add quit/help behavior/hint, for other tool portability

Issuing 'quit'/'exit' in an empty psql buffer exits psql.  Issuing
'quit'/'exit' in a non-empty psql buffer alone on a line with no prefix
whitespace issues a hint on how to exit.

Also add similar 'help' hints for 'help' in a non-empty psql buffer.

Reported-by: Everaldo Canuto
Discussion: https://postgr.es/m/flat/CALVFHFb-C_5_94hueWg6Dd0zu7TfbpT7hzsh9Zf0DEDOSaAnfA%40mail.gmail.com

Author: original author Robert Haas, modified by me

diff --git a/src/bin/psql/mainloop.c b/src/bin/psql/mainloop.c
index a8778a57aa79f6371f9b3ac887eecc320a83d700..a3ef15058fcb66c3968c3e6f3a77632dbef2d6fd 100644 (file)
--- a/src/bin/psql/mainloop.c
+++ b/src/bin/psql/mainloop.c
@@ -216,21 +216,108 @@ MainLoop(FILE *source)
                        continue;
                }
 
-               /* A request for help? Be friendly and give them some guidance */
-               if (pset.cur_cmd_interactive && query_buf->len == 0 &&
-                       pg_strncasecmp(line, "help", 4) == 0 &&
-                       (line[4] == '\0' || line[4] == ';' || isspace((unsigned char) line[4])))
+               /* Recognize "help", "quit", "exit" only in interactive mode */
+               if (pset.cur_cmd_interactive)
                {
-                       free(line);
-                       puts(_("You are using psql, the command-line interface to PostgreSQL."));
-                       printf(_("Type:  \\copyright for distribution terms\n"
-                                        "       \\h for help with SQL commands\n"
-                                        "       \\? for help with psql commands\n"
-                                        "       \\g or terminate with semicolon to execute query\n"
-                                        "       \\q to quit\n"));
+                       char       *first_word = line;
+                       char       *rest_of_line = NULL;
+                       bool            found_help = false;
+                       bool            found_exit_or_quit = false;
 
-                       fflush(stdout);
-                       continue;
+                       /* Search for the words we recognize;  must be first word */
+                       if (pg_strncasecmp(first_word, "help", 4) == 0)
+                       {
+                               rest_of_line = first_word + 4;
+                               found_help = true;
+                       }
+                       else if (pg_strncasecmp(first_word, "exit", 4) == 0 ||
+                                        pg_strncasecmp(first_word, "quit", 4) == 0)
+                       {
+                               rest_of_line = first_word + 4;
+                               found_exit_or_quit = true;
+                       }
+
+                       /*
+                        * If we found a command word, check whether the rest of the line
+                        * contains only whitespace plus maybe one semicolon.  If not,
+                        * ignore the command word after all.
+                        */
+                       if (rest_of_line != NULL)
+                       {
+                               /*
+                                * Ignore unless rest of line is whitespace, plus maybe one
+                                * semicolon
+                                */
+                               while (isspace((unsigned char) *rest_of_line))
+                                       ++rest_of_line;
+                               if (*rest_of_line == ';')
+                                       ++rest_of_line;
+                               while (isspace((unsigned char) *rest_of_line))
+                                       ++rest_of_line;
+                               if (*rest_of_line != '\0')
+                               {
+                                       found_help = false;
+                                       found_exit_or_quit = false;
+                               }
+                       }
+
+                       /*
+                        * "help" is only a command when the query buffer is empty, but we
+                        * emit a one-line message even when it isn't to help confused
+                        * users.  The text is still added to the query buffer in that
+                        * case.
+                        */
+                       if (found_help)
+                       {
+                               if (query_buf->len != 0)
+#ifndef WIN32
+                                       puts(_("Use \\? for help or press control-C to clear the input buffer."));
+#else
+                                       puts(_("Use \\? for help."));
+#endif
+                               else
+                               {
+                                       puts(_("You are using psql, the command-line interface to PostgreSQL."));
+                                       printf(_("Type:  \\copyright for distribution terms\n"
+                                                        "       \\h for help with SQL commands\n"
+                                                        "       \\? for help with psql commands\n"
+                                                        "       \\g or terminate with semicolon to execute query\n"
+                                                        "       \\q to quit\n"));
+                                       free(line);
+                                       fflush(stdout);
+                                       continue;
+                               }
+                       }
+                       /*
+                        * "quit" and "exit" are only commands when the query buffer is
+                        * empty, but we emit a one-line message even when it isn't to
+                        * help confused users.  The text is still added to the query
+                        * buffer in that case.
+                        */
+                       if (found_exit_or_quit)
+                       {
+                               if (query_buf->len != 0)
+                               {
+                                       if (prompt_status == PROMPT_READY ||
+                                               prompt_status == PROMPT_CONTINUE ||
+                                               prompt_status == PROMPT_PAREN)
+                                               puts(_("Use \\q to quit."));
+                                       else
+#ifndef WIN32
+                                               puts(_("Use control-D to quit."));
+#else
+                                               puts(_("Use control-C to quit."));
+#endif
+                               }
+                               else
+                               {
+                                       /* exit app */
+                                       free(line);
+                                       fflush(stdout);
+                                       successResult = EXIT_SUCCESS;
+                                       break;
+                               }
+                       }
                }
 
                /* echo back if flag is set, unless interactive */