how to write an empty line in file from a variable?

Question

In Windows Command Line I normally write empty line in a file with

echo; >> file

However, what I have now is a variable

$param1%

If I want echo to write it in the file I have to do

echo %param1% >> file

HERE IS WHERE THE PROBLEM START :

If I'd like an empty like I'd make

set param1=;

However since the ; is not in contact with the echo word the command is

echo ; >> file

which write the ; in the file...

I need the variable to sometime contains text, and sometime nothing. How can I do it?

Loïc MICHEL · Accepted Answer · 2015-07-10 14:53:24Z

1

if "%param1%"=="" echo;>>file else echo %param1%>>file

answered Jul 10, 2015 at 14:53

Loïc MICHEL

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Comments

JosefZ · Accepted Answer · 2015-07-10 19:46:04Z

1

If a param1 variable does not exist (the same as set "param1="), then %param1% results to:

In a .bat script: %param1% results to an empty string (a string of zero length);
In a CLI window: %param1% results to the %param1% string.

In a .bat script use (note no spaces surrounding %param1%)

>> file (echo;%param1%)

In a CLI window use

>>file (if not defined param1 (echo;) else echo;%param1%)

Note proper using of parentheses in if-else! For instance, check interesting result of next command:

if  ""=="" echo;"THEN branch">>file else echo;"ELSE branch">>file

Output:

==>if  ""=="" echo;"THEN branch">>file else echo;"ELSE branch">>file

==>type file
"THEN branch" else echo;"ELSE branch"

answered Jul 10, 2015 at 15:43

JosefZ

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