findstr returns nothing in windows batch script

Question

In windows cmd, temp dir is set to

 C:\spec>echo %temp%
 C:\Users\mahmood\AppData\Local\Temp

also there is a file %temp%\specdev.txt which contain

 C:\spec>type %temp%\specdev.txt
 c:\cpu

Now when I execute this command

findstr -r "^[a-zA-Z]:$" %temp%\specdev.txt >nul 2>&1

it doesn't return anything!!

C:\spec>findstr -r "^[a-zA-Z]:$" %temp%\specdev.txt >nul 2>&1

C:\spec>

What is the problem?? Can you explain what does this command do? it is part of a batch script.

Answer 1

You cannot see any results because all console outputs are redirected to NUL: the last part of the command >nul redirects standard output to NUL and 2>&1 redirects error output to standard output (therefore, NUL).

Because this command is part of a script, it does not mean it is useless: FINDSTR sets the global environment variable %ERRORLEVEL% to 0 when it finds a match and set it to 1 when doesn't find. Thus, a script can send all output to NUL (not to clog user screen) and check %ERRORLEVEL% to verify the results.

About the pattern this command is searching for, "^[a-zA-Z]:$" means that it searches for a line that only contains a single letter from "a" to "z" (uppercase and lowercase) and ends with a colon ":". Thus, the file %temp%\specdev.txt you described will not match the expression.

Answer 2

The problem is that the string doesn't match the regular expression, which matches lines that consist of nothing but a single letter followed by ':' character.

So now the question is, what pattern do you really want to match? Maybe you want:

"^[a-zA-Z]:"

which will match lines that start with a letter followed by a ':' (but can then have other characters following that on the line). But I suspect you want something more complex.

Answer 3

Try this code instead:

findstr -r "^[a-zA-Z]*$" %temp%\specdev.txt >nul 2>&1