Question

I am encountering a very weird situation when wrapping a bash script call in echo $(). This is strange enough that I don’t know what code to present, so I will describe the general situation. I have a script, which we will call “run.sh”, and it has some output. This is generally formatted quite nicely, with whitespace and line breaks.

I am trying to compare this output with a value that I got when I ran it once previously. To do this, the code compares the “new” value with the old by checking if these two are the same, i.e.:

expression=$(./runProcess.sh "$process");
expected=$(cat UnitTests/expect-process-$process);
if [ "$expression" == "$expected" ]; then

Clearly to get a value of “old” to compare with future testings I need to compute $(./runProcess.sh) by hand. When I do this, I get a version of the output with significantly less whitespace. However it is clearly wrong, because the contents of ls turn up in the middle of it. By that I mean that I get the following type of output running these two commands:

./runProcess.sh g,g:

R2With2Gluons =

    + ncol*i_*pi_^2*A*g^2 * (
       - 17/24*d_(mu1,mu2)*d_(m1,m2)*p1.p1
       - 31/8*d_(mu1,mu2)*d_(m1,m2)*p1.p2
       - 17/24*d_(mu1,mu2)*d_(m1,m2)*p2.p2
       + 7/12*d_(m1,m2)*p1(mu1)*p1(mu2)
       + 1/24*d_(m1,m2)*p1(mu1)*p2(mu2)
       + 89/24*d_(m1,m2)*p1(mu2)*p2(mu1)
       + 7/12*d_(m1,m2)*p2(mu1)*p2(mu2)
       );

 0.01 sec out of 0.01 sec


echo $(./runProcess.sh g,g):
R2With3Gluons = + coeff(m1,m2,m3)*ncol*pi_^2*A*g^3 Auto Diagrams UnitTests colourCalc.frm form.set functions.frm output.frm process.frm process.mid qgraf2form.frm qgrafProcessor.py runProcess.sh runProcesses.sh test vertices.frm ( + 35/24*d_(mu1,mu2)*p1(mu3) - 35/24*d_(mu1,mu2)*p2(mu3) - 35/24*d_(mu1,mu3)*p1(mu2) + 35/24*d_(mu1,mu3)*p3(mu2) + 35/24*d_(mu2,mu3)*p2(mu1) - 35/24*d_(mu2,mu3)*p3(mu1) ); 0.40 sec out of 0.40 sec

And here is ls:

ls:
Auto              form.set          process.mid       runProcesses.sh
Diagrams          functions.frm     qgraf2form.frm    test
UnitTests         output.frm        qgrafProcessor.py vertices.frm
colourCalc.frm    process.frm       runProcess.sh

I can provide exact examples if necessary, but I hope this is illuminating enough. Why could this possibly be happening? I’m using bash on OS X Mountain Lion.

Answer 1

Use more quotes!!!

Try:

echo "$(./run.sh)"

instead. (Yes, with quotes).

Try:

old=$(./run.sh)
echo "$old"

you’ll have the correct output (with $old in quotes). Now, regarding your test, use, as advised by sampson-chen:

[[ "$old" == "$(./run.sh)" ]]

(you don’t need to quote the variables or the command substitution when assigning the variable old, but, as a general rule, you can use quotes every time). ((see Gordon Davisson’s excellent comments to this post, that I’ve actually upvoted, with a few caveats about globs and quoting variables inside [[ ... ]])).

Edit. As you’ve edited your post, I see you’re using an inefficient cat. Instead of:

expected=$(cat UnitTests/expect-process-$process)

please use

expected=$(< "UnitTests/expect-process-$process")