Batch not-equal (inequality) operator

Question

According to this, !==! is the not-equal string operator. Trying it, I get:

C:\> if "asdf" !==! "fdas" echo asdf
!==! was unexpected at this time.

What am I doing wrong?

Solution 1

Try

if NOT "asdf" == "fdas" echo asdf

Solution 2

Use NEQ instead.

if "asdf" NEQ "fdas" echo asdf

Solution 3

I know this is quite out of date, but this might still be useful for those coming late to the party. (EDIT: updated since this still gets traffic and @Goozak has pointed out in the comments that my original analysis of the sample was incorrect as well.)

I pulled this from the example code in your link:

IF !%1==! GOTO VIEWDATA
REM  IF NO COMMAND-LINE ARG...
FIND "%1" C:\BOZO\BOOKLIST.TXT
GOTO EXIT0
REM  PRINT LINE WITH STRING MATCH, THEN EXIT.

:VIEWDATA
TYPE C:\BOZO\BOOKLIST.TXT | MORE
REM  SHOW ENTIRE FILE, 1 PAGE AT A TIME.

:EXIT0

!%1==! is simply an idiomatic use of == intended to verify that the thing on the left, that contains your variable, is different from the thing on the right, that does not. The ! in this case is just a character placeholder. It could be anything. If %1 has content, then the equality will be false, if it does not you'll just be comparing ! to ! and it will be true.

!==! is not an operator, so writing "asdf" !==! "fdas" is pretty nonsensical.

The suggestion to use if not "asdf" == "fdas" is definitely the way to go.

Solution 4

Try:

if not "asdf" == "fdas" echo asdf

That works for me on Windows XP (I get the same error as you for the code you posted).

Solution 5

NEQ is usually used for numbers and == is typically used for string comparison.

I cannot find any documentation that mentions a specific and equivalent inequality operand for string comparison (in place of NEQ). The solution using IF NOT == seems the most sound approach. I can't immediately think of a circumstance in which the evaluation of operations in a batch file would cause an issue or unexpected behavior when applying the IF NOT == comparison method to strings.

I wish I could offer insight into how the two functions behave differently on a lower level - would disassembling separate batch files (that use NEQ and IF NOT ==) offer any clues in terms of which (unofficially documented) native API calls conhost.exe is utilizing?

View more solutions

Comments

[Anders]

this requires command extensions to be turned on (They are by default on 2000+ but can be turned off system wide or as a parameter to cmd.exe) Normally you should turn them on with setlocal, but for a simple if not equal test, just use "if not", it goes back to the good old DOS days

[user66001]

Thanks jatrim.. Most definitely helpful for those searching for an answer, rather than asking the question again. It isn't like StackExchange locks off the ability to answer/comment due to age of questions, so think this is fully acceptable.

[Goozak]

The ! are used here in case %1 is empty, thus resulting in the test !==!, which is true. You could use %1.==. instead (almost any character would do) — the purpose being to make sure that both sides of the equality test has something to test. The !==! notation is definitely NOT a not-equal sign. Better stick with if not ....

[Jouni Aro]

Yeah, I usually use 'if X%1 == X goto somewhere' to check if the script has no arguments. It's the same as 'if "%1" == "" goto somewhere', except that will fail in batch files, because "" evaluates to nothing and the whole sentence reduces to 'if %1 == goto somewhere'. I prefer X, since ! makes you think it's a special operator, whereas it's just used as an extra character to overcome the problem with an empty string. Batch files are relics from the 1980's...