I thought that batch files would allow for empty variable to be output as a null string (""). If I set var1 to nothing, I thought I should
set "var1="
echo Variable value is: %var1%
I thought I'd get this:
Variable value is:
I actually get this as the output:
Variable value is: %var1%
Why isn't the var1 variable evaluating a blank string? For the record, I tested this with a new CMD instance in Windows 7.
Related
I would access the value of a variable. The name of the variable I want to access is stored in another variable and/or passed by argument to the batch.
So, I want to achieve two things:
calling batch with desired variable name as argument (and batch accessing the var directly):
--> command line==batch.bat myVar
{batch file:}
echo (what is in variable myVar)
calling batch with variable name that holds another varibale's name and output that other variable:
Let's assume that the variable "var_name" exists and has the value "APPDATA"
--> command line==batch.bat var_name
{batch file==}
echo (what is in variable APPDATA)
Not 100% sure why you need this, but I am assuming you want something like:
#echo off & setlocal enabledelayedexpansion
set "var=appdata"
for %%i in (!%1!) do (
echo original val from variable "%1" = "%%i"
echo secondary val from variable "%%i" = "!%%i!"
)
Here, I have set a temp value for var to be appdata. When running scriptname.cmd var you'll get the relevant results for both variables var and its value appdata
echo %time:~-5% returns a 5-character string, such as
18.09
However, i cannot seem to set that string to a variable:
set start = %time:~-5%
echo %start%
returns
10:07:18.09
what's simple way to get those last 5 chars into a variable?
thx
Windows doesn't like space next to =. So try this ...
set start=%time:~-5%
echo %start%
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?
if "%param1%"=="" echo;>>file else echo %param1%>>file
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"
I am new to linux shell script. i want that my script read a property file and save the value in any variable , the same which i can pass in same script..
as i wrote script is not fulfilling my requirement:
!/bin/bash
. test1
flat
if [ "$1" == test1 ]; then
flat=$1; /assign value to var flat
echo "flat"
fi
test1 is property file which includes :
la=12
tu=15
now i want when i run:
./myscript la
it read it from property file and store the value in flat variable.
Please help me.
You just need to use indirect referencing, but to do so, you need to store the value of the special parameter $1 in a regular parameter first.
!/bin/bash
. test1
var="$1"
# Only assign to flat if the variable specified in var is defined
if [ -n "${!var:-}" ]; then
flat="${!var}"; # assign value to var flat
echo "flat"
fi
First, ${!var} expands to the value of the variable whose name is in var. If var is "foo", it's the same as $foo. If var is "baz", it's the same as $baz.
${var:-default} expands to the value of var if it is set and has a non-null value. Otherwise, it expands to whatever you have after the ':-', in this case the string default. If there is no string, it uses the null value. So ${var:-} would expand to the null string if var was not set (or was already the null string).
Combining the two, ${!var:-} takes the variable var, and uses its value as a variable name. It then tries to expand that variable, and if it isn't set or is null, expand to the null string. So if var is la, it expands to the value of la. If var is re, and there is no variable re set, it expands to the null string.
Finally, the -n operator tests if its argument is non-zero length. In other words, it checks that the result of trying to expand the variable whose name is in var is not the null string. If that's true, then expand it again (yes, it's a little redundant) and assign its value to flat.
As the answer is written above, the variable flat is undefined if the argument to the script is not the name of a variable set in test1. If you don't mind flat being set regardless (say, flat=""), you don't need the if statement. You can just use one line to set the value of flat:
#!/bin/bash
. test1
var="$1"
flat="${!var:-}"
If I understood correctly you want to achieve an indirect variable dereferencing (see e.g. this example).
The solution is to use eval:
eval flat=\$$1
I want to assign the alpha numeric value to one variable in Batch scripting.
I tried following one but getting error.
setlocal
set test = \765514e2aad02ca658cc56cdb7884947 *E:\\test1
echo %test%
endlocal
Error:
C:\Users\bgannu>setlocal
C:\Users\bgannu>set test = \765514e2aad02ca658cc56cdb7884947 *E:\\test1
C:\Users\bgannu>echo 0
0
C:\Users\bgannu>endlocal
The syntax for set is set [[/a [expression]] [/p [variable=]] string]
The = has to be directly after your variable so you need to change:
set test = \765514e2aad02ca658cc56cdb7884947 *E:\\test1
to:
set test=\765514e2aad02ca658cc56cdb7884947 *E:\\test1
Otherwise your variable name would have a space at the end. You can easily try this out:
> set bar = foo
> echo %bar%
%bar%
> echo %bar %
foo
Note that both the variable name and its content got a space.
Lose the /A. the /A is used for arithmetic.
C:\test>set var=\765514e2aad02ca658cc56cdb7884947 *E:\\test1
C:\test>echo %var%
\765514e2aad02ca658cc56cdb7884947 *E:\\test1