Command output to a file with batch scripting

Question

I am trying to generate an xml file. I compare two images using a command which returns a number. But when I try to redirect its output to a file, it prints the number with a newline character.

        echo a.jpg >> "result.txt"
        compare -metric NCC "a.jpg" "b.jpg" "c.jpg" 2>> "result.txt"

Expected output like:

        a.jpg 1

But it outputs:

        a.jpg
        1

I tried to get the result from the command and tried to concatenate with the a.jpg but I couldn't have managed.

        for /f "tokens=1 delims=" %%a in ('compare -metric NCC "a.jpg" "b.jpg" "c.jpg"') do set result=%%a
        echo %result% 
        REM outputs 1ECHO is off.

what does for /f "tokens=1 delims=" %%a in ('compare -metric NCC "a.jpg" "b.jpg" "c.jpg"') do echo test %%a say? — Stephan
– Stephan, Commented Jun 23, 2015 at 19:41
It says 1ECHO is off but that means result variable hasn't been initialized right? — ozcanovunc
– ozcanovunc, Commented Jun 23, 2015 at 19:43
Sorry I tested the wrong cote btw. Your code outputs 1 only. But when I delete the test %%a part, the output stays same which is interesting. — ozcanovunc
– ozcanovunc, Commented Jun 23, 2015 at 20:29

Stephan · Accepted Answer · 2015-06-23 20:47:06Z

2

now I know, what happens:

compare -metric NCC "a.jpg" "b.jpg" "c.jpg" 2>> "result.txt"

your desired output is on STDERR, not on STDOUT (very unusual). But for captures STDOUT only.

It should be possible do adapt the forconstruct, but it's simpler to use:

<nul set /p "=a.jpg " >> "result.txt"
REM this line writes a string without linefeed

compare -metric NCC "a.jpg" "b.jpg" "c.jpg" 2>> "result.txt"
REM this line appends the STDERR of the "compare" command to the line

answered Jun 23, 2015 at 20:47

Stephan

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2 Comments

ozcanovunc Over a year ago

That worked but why do we need <nul,what is the aim of using it? (I am new to batch programming btw)

Stephan Over a year ago

set /p is intended to ask the user for input. We mis-use it for writing a line without linebreak; to simulate an empty user input, we redirect the NUL device to it. Try set /p "x=Give me Input: " You'll notice, that your input keeps on the same line, just after the "give me input" prompt. It's a bit like cheating, but works well and is commonly used.

norekhov · Accepted Answer · 2015-06-23 20:31:39Z

2

First command adds a newline. Use it like this to avoid it and get output in one line.

echo|set /p=a.jpg >> "result.txt"

answered Jun 23, 2015 at 20:31

norekhov

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