Question

i am working on a batch script.

i want to store the count of row’s in variable.

like

set var = mysql -uroot -proot -e”select count(*) from table”;

i also tried to do it other way like

 set var= mysql -uroot -proot -e "select count(*) from table into outfile 'F:\count.txt'";

 for /f %%a in ("F:\count.txt") do ( 
set output = %%a
echo %output% 

pause 

)

In above code the variable “output” shows nothing(empty).

please help me out.

Answer 1

I can see at least two issues in your script:

1. A string in double quotes inside IN( ) is treated as a literal, not as a file path/name, unless you specify the usebackq option, which enforces different semantics, whereby either double-quoted string or non-quoted one is treated as a file name.

2. You are storing <space>%%a into the output<space> variable, not %%a into output.

After you’ve fixed those two, there will remain one (probably, just one) more issue. You are assigning a value to a variable and then evaluating the variable in the same bracketed block (which is your loop body) using immediate variable expansion (%var%). This cannot work as expected. The thing is, a bracketed block is parsed entirely as a single unit, i.e. all its commands are parsed before the first one executes. As you can guess, your %output% expression will in this case evaluate to nothing, because output is not yet assigned a value at the time of parsing. (And when it is assigned a value, it will change nothing, because the previous (empty) value will already have replaced the expression.)

You can solve this using delayed variable expansion, which, as can be guessed, uses a different timing for evaluation. First, you should enable delayed expansion by issuing the SETLOCAL EnableDelayedExpansion command, then use a slightly different syntax: !var! instead of %var%.

So, if we address all the issues mentioned above, the loop may look like this:

…
SETLOCAL EnableDelayedExpansion

FOR /F "usebackq" IN ("F:\count.txt") DO (
SET output=%%a
ECHO !output!
)