Batch programming tip#08 (part 3): Reading from a file - Looping

This post will bring an end (I think) to this thread about file reading using batch.

To use the loop command on a file we simply add /F in our FOR loop construct like so:

@echo off

:init_vars
if exist file1.txt goto action
echo Oops. file1.txt doesn't exist. Please create it or change file name.
goto eof

:action
for /F %%l in (file1.txt) do (
echo Content: %%l
)
goto eof

:eof
echo Press any key to close window...
pause > nul
goto blackhole

:blackhole

This will probably work with most configuration files you might use. There is one additional parameter that's really useful though, especially if your lines contain spaces. The FOR loop will by default only return the first token up to a delimiter character. The default delimiter characters are space and tab. This means the script above will only return the first word of any line containing spaces.

To avoid this (usually unwanted) behaviour, use the delims parameter and set it to empty as in the following code:

@echo off

:init_vars
if exist file1.txt goto action
echo Oops. file1.txt doesn't exist. Please create it or change file name.
goto eof

:action
for /F "delims=" %%l in (file1.txt) do (
echo Content: %%l
)
goto eof

:eof
echo Press any key to close window...
pause > nul
goto blackhole

:blackhole


Notice how we have added to our for construct:
for /F "delims=" %%l in (file1.txt) do

You can set "delims=" to whatever you want in effect, you could for instance use comma instead: "delims=,".

Well, I think that's it, you can of course take file reading much further if you want. In that case, you might want to check Rob van der Woude's comprehensive page about NT FOR syntax. Enjoy!

More shortly about how to loop through directories.

Thoughts in the meantime?

Batch programming tip#08 (part 2): Reading from a file - Looping

So, let's see how we can loop through information.
The following script is the same as the previous but I have added a loop construct which will loop through our file_content variable (the first line of the file).

@echo off

:init_vars
if exist file1.txt goto action
echo Oops. file1.txt doesn't exist. Please create it or change file name.
goto eof

:action
set /P file_content=<file1.txt
for %%l in (%file_content%) do (
echo Content: %%l
)
goto eof

:eof
echo Press any key to close window...
pause > nul
goto blackhole

:blackhole

The loop construct is simple: for %%varname in (%var%) do ( ..[action]..)
The parentheses around the %var% are not in there just for form, you really need to remember them or your batch will crash.

To test it try using a file that contains a first line with spaces in it (e.g. The quick brown fox jumps over the lazy dog) and you will see that each word of the first line of the file will appear on a line of its own.

Excellent, the next step will be to loop through all the lines in a file.

Thoughts in the meantime?