A
Aaron
is this possible in cmd without writing a batch file?
ie
c:/>cd windows;cd system32
c:/windows/system32>
Aaron
ie
c:/>cd windows;cd system32
c:/windows/system32>
Aaron
T
Torgeir Bakken \(MVP\)
Hi,Aaron said:
C:\>cd %windir% && cd system32
C:\WINNT\SYSTEM32>
&& means "Do the command after && if the command before && succeeded".
T
Todd Vargo
Torgeir Bakken (MVP) said:
I've seen this a number of times but can not figure what exactly determines
if the command before succeeded. I'm guessing an errorlevel of zero.
However, some programs return non-zero values for success too.
So what is the criteria for && to mean a program succeeded?
W
William Allen
did not complete successfully=receives an error code greater than zero
Quoted from:
http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/ntcmds_o.mspx
under sub-item Concepts, sub-sub-item Command Shell Overview
===Quote starts
&& [...]
command1 && command2
Use to run the command following && only if the
command preceding the symbol is successful. Cmd.exe
runs the first command, and then runs the second command
only if the first command completed successfully.
|| [...]
command1 || command2
Use to run the command following || only if the command
preceding || fails. Cmd.exe runs the first command, and
then runs the second command only if the first command did
not complete successfully (receives an error code greater
than zero).
===End quote
============Screen capture Windows 2000 simulated in Win95
C:\WORK>echo n|choice || echo counts as failed
[Y,N]?N
counts as failed
C:\WORK>echo n|choice && echo counts as failed
[Y,N]?N
C:\WORK>
============End screen capture
T
Todd Vargo
William Allen said:
==== Windows XP screen capture
E:\>echo test && echo success
test
success
E:\>echo /? && echo success
Displays messages, or turns command-echoing on or off.
ECHO [ON | OFF]
ECHO [message]
Type ECHO without parameters to display the current echo setting.
E:\>echo /? || echo success
Displays messages, or turns command-echoing on or off.
ECHO [ON | OFF]
ECHO [message]
Type ECHO without parameters to display the current echo setting.
success
E:\>rem /? && echo success
Records comments (remarks) in a batch file or CONFIG.SYS.
REM [comment]
success
E:\>
==== end capture
Why is displaying ECHO's help considered a failure but REM's is not? Also,
since I can set errorlevel to any value before the test and it will be
unchanged afterwards, it seems the errorlevel state is bypassed/ignored.
ISTM, Microsoft's explanation for && and || operation does not hold water.
The result above is inconsistent with the documentation.
W
William Allen
in message
....snip
There's documentation and there's documentation
As I've remarked before, part of the task of learning Batch is to
refine and further define the documentation. So, as to && and ||,
the situation appears to be:
SomeCommand && Echo success message
SomeCommand || Echo failure message
(a) If SomeCommand sets the ERRORLEVEL then:
If ERRORLEVEL set is 0: && statement executed
|| statement not executed
If ERRORLEVEL set to non-zero: || statement executed
&& statement not executed
(b) If SomeCommand doesn't change the ERRORLEVEL then:
Regardless of current ERRORLEVEL, neither success nor failure
is defined and both && and || act as a normal command separator,
in other words both && and || act as &
This refinement is more-or-less what I'd take the Microsoft
documentation to mean, although (b) is not spelled out at all
(but I guess they'd argue it's "sort of" implied
OK, so what about REM?
I'd say this is a particular case for which you've discovered a new
(bug)/(feature of command parsing) that applies to REM (REM has more
code that has to handle ignoring |, >, >>, <, ||, and && in _true_
comments, so it's feasible that there could be a REM-specific bug in
the && and || handler). So noted.
Are there any cases other than REM that appear to contradict my
(a) and (b) version of Microsoft's documentation?
....snip
There's documentation and there's documentation
As I've remarked before, part of the task of learning Batch is to
refine and further define the documentation. So, as to && and ||,
the situation appears to be:
SomeCommand && Echo success message
SomeCommand || Echo failure message
(a) If SomeCommand sets the ERRORLEVEL then:
If ERRORLEVEL set is 0: && statement executed
|| statement not executed
If ERRORLEVEL set to non-zero: || statement executed
&& statement not executed
(b) If SomeCommand doesn't change the ERRORLEVEL then:
Regardless of current ERRORLEVEL, neither success nor failure
is defined and both && and || act as a normal command separator,
in other words both && and || act as &
This refinement is more-or-less what I'd take the Microsoft
documentation to mean, although (b) is not spelled out at all
(but I guess they'd argue it's "sort of" implied
OK, so what about REM?
I'd say this is a particular case for which you've discovered a new
(bug)/(feature of command parsing) that applies to REM (REM has more
code that has to handle ignoring |, >, >>, <, ||, and && in _true_
comments, so it's feasible that there could be a REM-specific bug in
the && and || handler). So noted.
Are there any cases other than REM that appear to contradict my
(a) and (b) version of Microsoft's documentation?
W
William Allen
(replaces earlier cancelled message)
in message
....snip
Useful points. So noted.
Treating:
ECHO /? || ECHO this will be displayed
ECHO /? && ECHO this will not be displayed
as the "rule" for /? help commands, are you aware of any other /?
exceptions apart from the REM command?
And are you aware of any other apparent inconsistencies in && and ||
handling apart from the /? treatment?
Motto for documentation fans:
"The only accurate program documentation is what the program does."
in message
....snip
Useful points. So noted.
Treating:
ECHO /? || ECHO this will be displayed
ECHO /? && ECHO this will not be displayed
as the "rule" for /? help commands, are you aware of any other /?
exceptions apart from the REM command?
And are you aware of any other apparent inconsistencies in && and ||
handling apart from the /? treatment?
Motto for documentation fans:
"The only accurate program documentation is what the program does."
T
Todd Vargo
William Allen said:
I've only tested about a half dozen commands, so I'm now aware of others
yet. If I have time, I might tinker with it again but if anyone is
interested in tinkering, I still don't see why displaying /? help is
considered a failure and how it is actually determined.
ECHO foo && ECHO this will be displayed
ECHO /? && ECHO this will not be displayed
Maybe one of those MVP's out there knows something about this. ;-)