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SHELL

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Samuel Gomes edited this page Nov 8, 2022 · 1 revision

The SHELL statement allows a program to run external programs or command line statements in Windows, macOS and Linux.

Syntax

SHELL [DOSCommand$]

SHELL [_DONTWAIT] [_HIDE] [DOSCommand$]

Description

  • If the DOSCommand$ STRING parameter isn't used, the "command console" is opened and execution is halted until the user closes it manually.
  • If _DONTWAIT is used, the QB64 program doesn't wait for the SHELLed program/command to end.
  • When the _HIDE action is used, the _CONSOLE window is hidden and screen info can be "redirected" (using redirection characters like >) to a file (recommended).
  • Commands are external commands, according to the user's operating system, passed as STRING enclosed in quotes or string variables.
  • Commands can be a mixture of STRING and string variables added together using the + concatenation operator.
  • Command text can be in upper or lower case. Use single spacing between items and options.
  • QB64 automatically uses CMD /C when using SHELL, but it is allowed in a command string. Note: CMD alone may lock up program.
  • Note: Some commands may not work without adding CMD /C to the start of the command line.
  • QB64 program screens will not get distorted, minimized or freeze the program like QBasic full-screen modes would.
  • QB64 can use long path folder names and file names and SHELL command lines can be longer than 124 characters.
  • In Windows, use additional CHR$(34) quotation marks around folder or file names that contain spaces.
  • For other operating systems, both the quotation mark character and the apostrophe can be used to enclose a file name that contains spaces.
  • NOTE: Use CHDIR instead of CD as SHELL commands cannot affect the current program path.

QBasic

  • QBasic BAS files could be run like compiled programs without returning to the IDE when SYSTEM was used to END them.
  • A user would invoke it with SHELL "QB.EXE /L /RUN program.BAS"

Example(s)

When working with file or folder names with spaces, add quotation marks around the path and/or file name with CHR$(34).

SHELL _HIDE "dir " + CHR$(34) + "free cell.ico" + CHR$(34) + " /b > temp.dir" 
SHELL "start Notepad temp.dir" ' display temp file contents in Notepad window

Contents of temp.dir text file:


Free Cell.ico

Opening a Windows program (Notepad) to read or print a Basic created text file.

INPUT "Enter a file name to read in Notepad: ", filename$
SHELL "CMD /C start /max notepad " + filename$  ' display in Notepad full screen in XP or NT   

'SHELL "start /min notepad /p " + filename$ ' taskbar print using QB64 CMD /C not necessary

Explanation: Notepad is an easy program to open in Windows as no path is needed. Windows NT computers, including XP, use CMD /C where older versions of DOS don't require any command reference. The top command opens Notepad in a normal window for a user to view the file. They can use Notepad to print it. The second command places Notepad file in the task-bar and prints it automatically. The filename variable is added by the program using proper spacing.

  • Start is used to allow a Basic program to run without waiting for Notepad to be closed.
  • /min places the window into the task-bar. /max is full-screen and no option is a normal window.
  • Notepads /p option prints the file contents, even with USB printers.

Function that returns the program's current working path.

 currentpath$ = Path$ ' function call saves a path for later program use
 PRINT currentpath$

 FUNCTION Path$   
   SHELL _HIDE "CD > D0S-DATA.INF"   'code to hide window in **QB64**
   OPEN "D0S-DATA.INF" FOR APPEND AS #1  'this may create the file
        L% = LOF(1)          'verify that file and data exist
   CLOSE #1   
   IF L% THEN                       'read file if it has data
     OPEN "D0S-DATA.INF" FOR INPUT AS #1
     LINE INPUT #1, line$           'read only line in file
     Path$ = line$ + "\"            'add slash to path so only a filename needs added later
     CLOSE #1
   ELSE : Path = ""                 'returns zero length string if path not found
   END IF
   KILL "D0S-DATA.INF"              'deleting the file is optional
 END FUNCTION

Explanation: The SHELL "CD" statement requests the current working path. This info is normally printed to the screen, but the > pipe character sends the information to the DOS-DATA.INF file instead(QB64 can use _HIDE to not display the DOS window). The function uses the OPEN FOR APPEND mode to check for the file and the data(INPUT (file mode) would create an error if file does not exist). The current path is listed on one line of the file. The file is opened and LINE INPUT (file statement) returns one line of the file text. The function adds a "" so that the Path$ returned can be used in another file statement by just adding a file name. Save the Path$ to another variable for later use when the program has moved to another directory. In QB64 you can simply use the _CWD$ statement for the same purpose of the example above.

Determining if a drive or path exists. Cannot use with a file name specification.

LINE INPUT "Enter a drive or path (no file name): ", DirPath$
IF PathExist%(DirPath$) THEN PRINT "Drive Path exists!" ELSE PRINT "Drive Path does not exist!"
END

FUNCTION PathExist% (Path$)
  PathExist% = 0
  IF LEN(Path$) = 0 THEN EXIT FUNCTION 'no entry
  IF LEN(ENVIRON$("OS")) THEN CMD$ = "CMD /C " ELSE CMD$ = "COMMAND /C "
  SHELL _HIDE CMD$ + "If Exist " + Path$ + "\nul echo yes > D0S-DATA.INF"
  OPEN "D0S-DATA.INF" FOR APPEND AS #1
  IF LOF(1) THEN PathExist% = -1             'yes will be in file if path exists
  CLOSE #1
  KILL "D0S-DATA.INF"               'delete data file optional
END FUNCTION

Explanation: IF Exist checks for the drive path. \Nul allows an empty folder at end of path. Echo prints yes in the file if it exists. In QB64 you can simply use the _FILEEXISTS statement for the same purpose of the example above.

Snippet 1: When looking for printers this command gives you a file list with the default printer marked as TRUE:

SHELL _HIDE "CMD /C" + "wmic printer get name,default > default.txt"

Created file's text:


Default  Name                           
  FALSE    Microsoft XPS Document Writer 
  TRUE     HP Photosmart C7200 series     
  FALSE    HP Officejet Pro 8600         
  FALSE    Fax

Explanation: LINE INPUT could be used to find the printer names as STRING variables.

Snippet 2: Here is the code to set the default printer to the "HP Officejet Pro 8600":

SHELL _HIDE "CMD /C" + "wmic printer where name='HP Officejet Pro 8600' call setdefaultprinter"

After executing this program, and then running the first snippet again, we see the following contents of the text file:


Default  Name 
  FALSE    Microsoft XPS Document Writer 
  FALSE    HP Photosmart C7200 series     
  TRUE     HP Officejet Pro 8600         
  FALSE    Fax

More examples

See examples in:

See Also

Extra reference

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