Why does for /f not ignore blank lines? - windows

Question

I'm trying to get a simple value from a for /f loop in a batch file.
Using the command wmic path win32_localtime get dayofweek gives me the output:
C:\sendemail>wmic path win32_localtime get dayofweek
DayOfWeek
1
C:\sendemail>
So, using the following batch script, I should be able to return a result of "1":
set cmd=wmic path win32_localtime get dayofweek
for /f "tokens=1 skip=1" %%Z in ('%cmd%') do set _myday=%%Z
echo Var is %_myday%
But I don't, it sets the variable at least twice, as seen here :
C:\sendemail>set cmd=wmic path win32_localtime get dayofweek
C:\sendemail>for /F "tokens=1 skip=1" %Z in ('wmic path win32_localtime get dayofweek') do set _myday=%Z
C:\sendemail>set _myday=1
:\sendemail>set _myday=
C:\sendemail>echo Var is
Var is
C:\sendemail>
At first, I wondered why, then I realised the loop is processing the two blank lines... which it shouldn't be. according to this: http://ss64.com/nt/for_cmd.html
Skip SKIP will skip processing a number of lines from the beginning of
the file. SKIP includes empty lines, but after the SKIP is complete,
FOR /F ignores (does not iterate) empty lines.
Either, it's not working normally, or those lines are not blank, and are filled with something...
At any rate, how do I get just the day of the week result out of this, and ignore the rest?

Answer 1

About the lines contents, yes, the output from wmic includes at the end of each line an additional carriage return character that is detected by the for command. That is the reason for your non empty lines.
You can try with
for /f "tokens=2 delims==" %%Z in ('
wmic path win32_localtime get dayofweek /value
') do for /f %%Y in ("%%Z") do set "_myday=%%Y"
The code is asking wmic to return the information in key=value format and using the equal sign to tokenize the input records. As we request only the second token, for will only process lines that return at least two tokens, lines having a key (first token), an equal sign (delimiter) and a value (second token)
But, the additional carriage return at the end of the line is also included in the value of the variable.
When the variable is used with normal syntax (%_myday%) it is not seen, but with delayed expansion (!_myday!) the additional carriage return will be echoed.
To remove this additional character from the variable, a second for command has been used in the posted code.

Answer 2

This slight midification will work:
#ECHO OFF
set cmd=wmic path win32_localtime get dayofweek
for /f "tokens=1 skip=1" %%Z in ('%cmd%') do (
set _myday=%%Z
GOTO BREAK
)
:BREAK
echo Var is %_myday%
PAUSE
Simply jump out of the loop after reading the desired line.

Answer 3

The above is a good approach and intitially I applied it successfully. Because of another need to capture a WMI variable and load into an environment variable, I wanted some that would be a native command line. I stumbled on this...
for /F "skip=2 tokens=2 delims=," %%i IN ('wmic timezone get Bias /format:csv') do (echo var Bias=%%i; > %TZONEDB%mid.htm )
The core is that using the CSV format makes skip work (no trailing blanks) and gives you easily parsed output.
ed g

Answer 4

I recently had the issue discussed here and whilst previous answers helped I wanted to retrieve several variables for subsequent testing. At first I used code similar to the following example (just not on explorer.exe and with different variable names. The following variable names have been deliberately chosen to match variable name restrictions in the later code).
setlocal
for /F "skip=2 tokens=2,3,4 delims=," %%a in ('
wmic /node:"MyFileServer-pc" process where Name^="explorer.exe"
get HandleCount^,
ParentProcessId^,
ThreadCount
/format:csv
') do (
set ProcHandleCount=%%a
set ProcParentProcessId=%%b
set ProcThreadCount=%%c
)
echo HandleCount %ProcHandleCount%, ParentProcessID %ProcParentProcessId%, ThreadCount %ProcThreadCount%
However, I dislike this solution as wmic always returns results in the order in which it internally iterates them disregarding the order in which they are presented to the wmic command, So the command wmic process where Name^="explorer.exe" get ThreadCount^,HandleCount^,ParentProcessId still returns ThreadCount last. This makes the previous code error prone when fetching multiple parameter value pairs and a hassle to get the ordering correct.
So instead I used the following code, which achieves the same result avoiding the need to care about the ordering of wmic parameters. It is also very easy to add additional parameters still with no need to care about ordering.
setlocal
for /F "tokens=1,2delims==" %%a in ('
wmic /node:"MyFileServer-pc" process where Name^="explorer.exe"
get HandleCount^,
ParentProcessId^,
ThreadCount
/value
') do #set Proc%%a^=%%b
echo HandleCount %ProcHandleCount%, ParentProcessID %ProcParentProcessId%, ThreadCount %ProcThreadCount%
In the above code, the variable naming is provided by the parameter of each returned parameter=value pair from wmic plus a fixed prefix, automatically matching returned parameter and value pairs. Note the use of a prefix, in this case 'Proc', without at least a one character prefix returned wmic blank lines cause errors. If different environment variable names are needed then the first solution allows freedom in naming and allows for shorter names but is more error prone when multiple values are required.
For what little it's worth... the following code avoids the variable prefixes and silences errors. More unique variable names would usually be desired.
(
for /F "tokens=1,2delims==" %%a in ('
wmic /node:"MyFileServer-pc" process where Name^="explorer.exe" get HandleCount^,ParentProcessId^,ThreadCount /value
') do #set %%a=%%b
) 2>nul
These examples use the wmic parameter /node:"MyFileServer-pc" to get remote process info but work equally for simpler wmic commands.

Answer 5

I always use this batch template when processing wmic output:
setlocal enableextensions enabledelayedexpansion
for /f "delims and such" %%a in ('wmic path win32_localtime get dayofweek 2^>nul ^<nul') do (
set VAR=%%a
CALL :RMCRLF VAR
if "!VAR!" NEQ "" (
rem If we get here, then it's a non-empty line
rem ... Do something ...
)
)
GOTO :EOF
:RMCRLF
:: All this does is clean stray carriage returns/line feeds off of a variable,
:: which wmic is notorious for injecting into its output.
set RMCRVAR=%1
IF NOT DEFINED RMCRVAR GOTO :EOF
CALL set %RMCRVAR%=%%%RMCRVAR%%%
GOTO :EOF
They key here is the "function" (if you will) :RMCRLF. It will strip the pesky carriage returns off of a variable so you can check for true emptiness of the string, and then decide to skip the empty line.