Batch File - Read specific line, and save a specific string in that line as a variable

Question

Is there any way to get for /f loop (or anything else) to read a specific line?

Here is the code I have so far, it reads first word of every line.

@echo         


        

Answer 1

Since you haven't fully defined what you mean by "a specific location", I'll make some (reasonable, in my opinion) assumptions, though the method I present is equally valid no matter what your definition turns out to be.

You can get arbitrary lines and arbitrary words on that line by using a line counter variable in conjunction with tokens.

Let's assume your text file name can be found as the second argument on the fourth line of the infile.txt file. You can get that with something like:

@setlocal enableextensions enabledelayedexpansion
@echo off
set /a "line = 0"
for /f "tokens=2 delims= " %%a in (infile.txt) do (
    set /a "line = line + 1"
    if !line!==4 set thing=%%a
)
endlocal & set thing=%thing%
echo %thing%

This actually uses a few "tricks" which warrant further explanation:

• the line counter to ensure you only grab what you want from a specific line, though you could change the test !line!==4 into anything you need such as a line beginning with #, the fifth line containing the string xyzzy and so on.
• the use of setlocal/endlocal to effectively give you a scope from which variables cannot leak. This is good programming practice even for a language often not normally associated with such things :-)
• the use of endlocal & set to bypass that scope so that thing is the only thing that does actually leak (as it should).
• the use of delayed expansion and !..! variables to ensure they're correct within the for loop. Without this, the %..% will always be expand to the value they were set to when the for loop started.

Those last two bullet points are actually related. %..% variables are expanded when the command is read rather than when it is executed.

For a for loop, the command is the entire thing from the for to the final ). That means, if you use %line% within the loop, that will be evaluated before the loop starts running, which will result in it always being 0 (the variable itself may change but the expansion of it has already happened). However, !line! will be evaluated each time it is encountered within the loop so will have the correct value.

Similarly, while endlocal would normally clear out all variables created after the setlocal, the command:

endlocal & set thing=%thing%

is a single command in the context of expansion. The %thing% is expanded before endlocal is run, meaning it effectively becomes:

endlocal & set thing=whatever_thing_was_set_to_before_endlocal

That's why the use of setlocal and endlocal & set is a very useful way to limit variables "escaping" from a scope. And, yes, you can chain multiple & set stanzas to allow more variables to escape the scope.