CODEWITHSUNDEEP
batch-file
Peter Frey
Peter Frey

Reputation: 365

BATCH check for empty variable by STRING NAME

is there some redirect from a string to a variable in batch?

main.cmd

@setlocal enableextensions Enabledelayedexpansion 
@echo off
set log=C:\log\test.log
set my_var=foo
set vars_to_check=my_var
call check_empty.cmd "%vars_to_check%"  || goto :error_handler

check_empty.cmd

if "%1" == "" (
    echo no param. >> !log!
    exit /b 2
    )
if not defined %1 ( 
    echo the variable %1 is empty.  >> !log!
    exit /b 1 
    )
echo %1 has value %%1%%.   >> !log!
exit /b 0

Now I did run main.cmd: I did expect the echo 'my_var has value foo.'. However, I just get 'the variable "%1" is empty.' Please note the quotes around %1. Therefore, I removed the quotes from the call in main.cmd and it almost worked, as I got the message: 'my_var has value %my_var%.'. At least I am arriving at the point where the variable is realized to be defined.

The problem with avoiding the quotes is that the next step would have been: pass multiple vars and loop the check...

set vars_to_check=my_var some_other_var something_else

and now I need the quotes so I can pass the variable...

Upvotes: 0

Views: 67

Answers (1)

Stephan
Stephan

Reputation: 56180

check_emtpy.cmd:

@echo off
if "%~1" == "" echo no param. & exit /b 2
if not defined %~1 echo the variable %1 is empty.& exit /b 1
call echo %1 has value %%%~1%% & exit /b 0
  • if the parameter (variable name) is empty, return (errorlevel 2)
  • if the variable isn't defined, return (errorlevel 1)
  • return (errorlevel 0)

If you don't need the message, the last line is optional. If you can guarantee that there is always a parameter (but who could guarantee that...), the first if is optional too.

Upvotes: 3

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