Run a bash command until diff between two files is non-empty [duplicate]

Question

I have a two versions of a program, say : normalProgram and bruteProgram.

I have an input generator for both of these : programGenerator

Now I want to do this:

Put the output of ./programGenerator into input.txt : ./programGenerator > input.txt
Redirect input.txt as the input of normalProgram : cat input.txt | ./normalProgram
- Put the output of ./normalProgram into op1.txt : (cat input.txt | ./normalProgram) > op1.txt
Similar thing for ./bruteProgram :
- (cat input.txt | ./bruteProgram) > op2.txt
Now I want to compare op1.txt and op2.txt : diff op1.txt op2.txt

The whole command will look like this:

./programGenerator > input.txt &&
(cat input.txt | ./normalProgram) > op1.txt &&
(cat input.txt | ./bruteProgram) > op2.txt &&
diff op1.txt op2.txt

So this is a one time command.

I want to run this until diff op1.txt op2.txt gives a non-empty response.

I tried putting diff op1.txt op2.txt as the condition for until (or while, just to check whether the conditional is correct)

But this didn't work, and I got an error that, that is not a correct conditional.

Example:

while [diff normalOp.txt bruteOp.txt]
do
echo "hello"
done

This is giving me the error:

zsh: bad pattern: [diff

Possible duplicate of "Bash conditional based on exit code of command". Also, if you did need to use square brackets, you'd need spaces around them. Finally, (cat input.txt | ./normalProgram) > op1.txt can be simplified to ./normalProgram < input.txt > op1.txt (which is also more efficient). — Gordon Davisson
– Gordon Davisson, Commented Jan 8, 2023 at 6:18

Mooncrater · Accepted Answer · 2023-01-08 05:36:21Z

0

I just had to remove the square brackets from the condition:

while diff normalOp.txt bruteOp.txt  
do
echo "hello"
done

And this started working.

The exact bash command in this case would be:

while diff op1.txt op2.txt
while> do
while> ./programGenerator > input.txt   
while> (cat input.txt | ./normalProgram) > op1.txt
while> (cat input.txt | ./bruteProgram) > op2.txt
while> done

edited Jan 8, 2023 at 5:36

answered Jan 8, 2023 at 5:30

Mooncrater

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1 Comment

user5774952 Over a year ago

The syntax error was one problem, but your current logic is "while diff produces some output, do a thing." What you have stated in the question would be "while diff produces no output, do a thing." This is for Bash, but should be similar in Zsh, though you could also make it simpler using until instead of while.

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