I know we could get substring like this in batch script:
SET a=abcdefgh
ECHO %a:~3,2%
But how can I get letter by a variable index? Kind like:
SET index=3
ECHO %a:~%index%,1%
Since the substring operation needs a constant it has to be called in a subprocess, that's when CALL comes in handy:
SET _index=3
call set b=%%a:~%index%,1%%
echo (%b%)
See https://ss64.com/nt/syntax-substring.html for more details. SS64/nt is an excellent resource for anything batch related.
Related
In python, you can evaluate strings like this:
eval("true")
which returns a boolean set to True
Is there a way to pass an entire command into a batch script argument like this:
my_script.bat "my_command -do_x=5 do_y=56 ...etc"
Then have the batch script set that argument in the quotes to a variable:
set execute_script=%1
And finally run it? In python we would do:
eval(execute_script)
How can I do this in batch script?
set "execute_script=%1"
%execute_script%
probably.
The eval function in python is very useful indeed, but it has signatures that defines the eval function to perform actual evaluations dynamically. That is sadly not something cmd has by default. What we can do is to evaluate if a variable is defined, which is not of much use comapred to eval.
So creating a variable, evaluating that it is defined then executing it as a macro:
#echo off
set "string=%*"
if defined string %string%
but that is useless if you simplify it by not creating macros:
if not "%1" == "" %*
I'm sure I'm missing something stupid. I want to pass a full path variable to a perl script, where I do some work on it and then pass it back. So I have:
echo "Backing up: $f ";
$write_file="$(perl /home/spider/web/foo.com/public_html/gen-path.cgi $f)";
echo "WRITE TO: $write_file \n";
However, this gives me:
Backing up: /home/spider/web/foo.com/public_html/websites-uk/uk/q/u
backup-files-all.sh: line 7: =backup-uk-q-u.tar.gz: command not found
WRITE TO: \n
I can't work out why its not saving the output into $write_file. I must be missing something (bash isn't my prefered language, which is why I'm passing to Perl as I'm a lot more fluent in that :))
Unless your variable write_file already exists, the command $write_file="something" will translate to ="something"(1).
When setting a variable, leave off the $ - you only need it if you want the value of the variable.
In other words, what you need is (note no semicolons needed):
write_file="$(perl /home/spider/web/foo.com/public_html/gen-path.cgi $f)"
(1) It can be even hairier if it is set to something. For example, the code:
write_file=xyzzy
$write_file="something"
will result in something being placed into a variable called xyzzy, not write_file :-)
Please consider the following very simple batch script (the file is named test.cmd):
#echo off
set "var1=%~1"
echo %var1%
The script should be called with one command line parameter, should assign the string which is contained in that parameter to a variable, and should output the variable.
As expected, I get an error message when I call this script with a command line parameter which contains an ampersand (&):
C:\Batch>test "a&b"
a
'b' is not recognized as an internal or external command,
operable program or batch file.
The reason for this has been discussed in some other questions here and elsewhere, for example that one; the usual remedy is to use delayed expansion. So I changed the script accordingly:
#echo off
setLocal enableDelayedExpansion
set "var1=%~1"
echo !var1!
Now it works with the parameter from before:
C:\Batch>test "a&b"
a&b
But there is a new problem. When the command line parameter contains an exclamation mark (!), it will be dropped from the output:
C:\Batch>test a!b
ab
This behavior also has been discussed at several places, for example here; the crucial thing to note is that dropping the exclamation mark happens during the assignment, not during the echo.
Despite a lot of research, I did not find a question here which provided an elegant solution for both problems at once. That is, is there an elegant way to assign a command line parameter to a variable when that parameter contains an ampersand AND an exclamation mark?
It seems that I need the delayed expansion to treat the ampersand correctly, but this destroys the exclamation mark.
The only solution I currently see is to not use delayed expansion and to add code to explicitly quote all ampersands in the input string. This would be so ugly that I seriously think that I am missing something here.
As a side note, the reason for the problem actually seems to be that there (IMHO!) is no way to get the command line parameter in a delayed-expanded fashion. The syntax for the first parameter is %~1, there is no such thing as !~1.
Move the setLocal enableDelayedExpansion after the the set„ that's all.
#echo off
set "var1=%~1"
setLocal enableDelayedExpansion
echo !var1!
I'm trying to replace a string passed as an argument to a batch file.
This works:
set PWD="%~dp1"
set "PWD=%PWD:\=/%"
Which puts the passed argument's parent directory path inside PWD variable, and then replaces \ characters to / characters.
Is there a way to achieve this one liner by execution of just one command instead of two?
Something like this: set "PWD=%~dp1:\=/%, however, that doesn't obviously work.
Please elaborate both methods, using DelayedExpansion and not using it.
Did you test this before posting it?
Your code will produce
PWD=\=/
If it produces the "correct result" then it's because you're not clearing pwd at the end of each run (usually by a setlocal directly after the #echo off) and hence the result will be NOT of the current %~dp1 but of the previous setting of pwd.
Your code first sets pwd to be "c:\whatever..." (including the quotes) PLUS the Space before the & and then sets pwd again to the prior value of pwd with \ replaced by /.
cmd will resolve any expression involving %var% first, and then executes the result. With delayedexpansion, !var! is evaluated at run-time and %var% at parse-time.
Since string-manipulation is not allowed on metavariables, the required operation cannot be condensed into a single statement; the value must be passed through an ordinary environment variable first.
To fix your statement, use
set "PWD=%~dp1" & CALL set "PWD=%%PWD:\=/%%"
which will perform the string-manipulation in a subshell after first assigning the value to pwd - moving the quote delimits the command that will be executed - following spaces after the closing quote will not be included in the value assigned.
I'm working on a Windows batch file that will bcp three text files into SQL Server. If something goes wrong in production, I want to be able to override the file names. So I'm thinking of doing something like this.
bcp.exe MyDB..MyTable1 in %1 -SMyServer -T -c -m0
bcp.exe MyDB..MyTable2 in %2 -SMyServer -T -c -m0
bcp.exe MyDB..MyTable3 in %3 -SMyServer -T -c -m0
I would like to be able to enter default names for all three files, to be used if the positional parameters are not supplied. The idea would be either to execute
myjob.bat
with no parameters, and have it use the defaults, or execute
myjob.bat "c:\myfile1" "c:\myfile2" "c:\myfile3"
and have it use those files. I haven't been able to figure out how to tell if %1, %2 and %3 exist and/or are null. I also don't know how to set those values conditionally. Is this possible? Any suggestions would be appreciated.
To test for the existence of a command line paramater, use empty brackets:
IF [%1]==[] echo Value Missing
or
IF [%1] EQU [] echo Value Missing
The SS64 page on IF will help you here. Under "Does %1 exist?".
You can't set a positional parameter, so what you should do is do something like
SET MYVAR=%1
You can then re-set MYVAR based on its contents.
The right thing would be to use a "if defined" statement, which is used to test for the existence of a variable. For example:
IF DEFINED somevariable echo Value exists
In this particular case, the negative form should be used:
IF NOT DEFINED somevariable echo Value missing
PS: the variable name should be used without "%" caracters.
Both answers given are correct, but I do mine a little different. You might want to consider a couple things...
Start the batch with:
SetLocal
and end it with
EndLocal
This will keep all your 'SETs" to be only valid during the current session, and will not leave vars left around named like "FileName1" or any other variables you set during the run, that could interfere with the next run of the batch file. So, you can do something like:
IF "%1"=="" SET FileName1=c:\file1.txt
The other trick is if you only provide 1, or 2 parameters, use the SHIFT command to move them, so the one you are looking for is ALWAYS at %1...
For example, process the first parameter, shift them, and then do it again. This way, you are not hard-coding %1, %2, %3, etc...
The Windows batch processor is much more powerful than people give it credit for.. I've done some crazy stuff with it, including calculating yesterday's date, even across month and year boundaries including Leap Year, and localization, etc.
If you really want to get creative, you can call functions in the batch processor... But that's really for a different discussion... :)
Oh, and don't name your batch files .bat either.. They are .cmd's now.. heh..
Hope this helps.
rem set defaults:
set filename1="c:\file1.txt"
set filename2="c:\file2.txt"
set filename3="c:\file3.txt"
rem set parameters:
IF NOT "a%1"=="a" (set filename1="%1")
IF NOT "a%2"=="a" (set filename2="%2")
IF NOT "a%3"=="a" (set filename1="%3")
echo %filename1%, %filename2%, %filename3%
Be careful with quotation characters though, you may or may not need them in your variables.
Late answer, but currently the accepted one is at least suboptimal.
Using quotes is ALWAYS better than using any other characters to enclose %1.
Because when %1 contains spaces or special characters like &, the IF [%1] == simply stops with a syntax error.
But for the case that %1 contains quotes, like in myBatch.bat "my file.txt", a simple IF "%1" == "" would fail.
But as you can't know if quotes are used or not, there is the syntax %~1, this removes enclosing quotes when necessary.
Therefore, the code should look like
set "file1=%~1"
IF "%~1"=="" set "file1=default file"
type "%file1%" --- always enclose your variables in quotes
If you have to handle stranger and nastier arguments like myBatch.bat "This & will "^&crash
Then take a look at SO:How to receive even the strangest command line parameters?