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20

How to save output from command (eg. diff) into a variable

rated 0 times [ 20] [ 0] / answers: 1 / hits: 49492 / 2 Years ago, fri, february 25, 2022, 2:29:50

I want to test if there is any output from the diff (test if files are same), if none echo "Passed $x" else echo "Failed $x". I came up with some intermidiate step (save the output from diff to a file then read from file)

diff "./helloworld$x.out" "./output/helloworld$x.out" > tmp.txt;

output="`cat tmp.txt`";



if [ "$output" = "" ];

  then

    echo "Passed $x";

  else

    echo "Failed $x";

  fi;

I'm sure the code can be improved? Main question is: is it possible to save the output from diff directly into a variable?

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3 Years ago

answered 2 Years ago jectedrin · Accepted Answer

This works:

if diff "./helloworld$x.out" "./output/helloworld$x.out" >/dev/null; then

    echo "Passed $x";

else

    echo "Failed $x";

fi

If you use a variable instead of echo you could drop the else branche: set the variable to false before the if and save 2 lines of code.

If you want to actually put the result into a variable use:

some_var="$(diff "./helloworld$x.out" "./output/helloworld$x.out")"

Including my test to see if it does actually work:



rinzwind@discworld:~$ touch 1

rinzwind@discworld:~$ touch 2

rinzwind@discworld:~$ more test

if diff 1 2 >/dev/null; then

    echo "Passed $x";

else

    echo "Failed $x";

fi

rinzwind@discworld:~$ ./test

Passed 



rinzwind@discworld:~$ vi 2

rinzwind@discworld:~$ more 2

2

rinzwind@discworld:~$ ./test

Failed

On the >/dev/null part: >/dev/null 2>&1 will send output to >/dev/null and 2>&1 will send standard errors to the same file (&1 means 'use first parameter') in front of this command (so it also uses /dev/null).

sidenote: sdiff will show a side-by-side diff listings:



sdiff 1 2 

1                               1

2                               2

3                               3

4                               4

5                                  5

7                               7

                                  > 8

9                               9

10                              10