Diff command in bash

Question

Every time i run the following bash command, i get an error:

Here's the code:

sort -b ./tests/out/$scenario > $studentFile
sort -b ./tests/out/$scenario > $profFile
$(diff $studentFile $profFile)
  if [ $? -eq 0 ]
      then 
          echo "Files are equal!"
      else
          echo "Files are different!"
      fi

Here's the error:

./test.sh: 2c2: not found

I basically want to sort two files, and then check if they are equal or not. What i don't understand is what this error means and how i can get rid of it. Any help will be greatly appreciated.

Thanks!

Any spaces, stars, or other special characters in the filenames or paths? — user000001
– user000001, Commented May 31, 2015 at 15:48

pasaba por aqui · Accepted Answer · 2020-07-30 18:57:49Z

7

Short answer: use

diff $studentFile $profFile

instead of:

$(diff $studentFile $profFile)

Long answer:

diff $studentFile $profFile

will provide an output of several lines, first one, in your example, is "2c2". If you enclose the diff command in $(), the result of this expression is an string with the concatenation of all the lines, "2c2 ...". In your script, this result is executed by bash as new command, with the result of "command not found: 2c2".

Compare, by example:

$(diff $studentFile $profFile)

and:

echo $(diff $studentFile $profFile)

*** Addendum ***

if diff $studentFile $profFile > /dev/null 2>&1
then
  echo "equal files"
else
  echo "different files"
fi

is a possible way of reach the expected result.

edited Jul 30, 2020 at 18:57

answered May 31, 2015 at 15:48

pasaba por aqui

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3 Comments

laker02 Over a year ago

Sorry i forgot the last part of the code i've edited it!

Kusalananda Over a year ago

Same problem there: remove all $( ... ) around the diff commands.

laker02 Over a year ago

Thanks, turned out it was an easy fix!

Kusalananda · Accepted Answer · 2016-06-22 07:46:40Z

2

Your command

$(diff $studentFile $profFile)

executes the result of running the diff command on the two files. The 2c2 that your shell complains about is probably the first word in the output from diff.

I'm assuming that you simply want to see the output from diff:

diff $studentFile $profFile

If you want to compare the file for equality in a script, consider using cmp:

if cmp -s $studentFile $profFile; then
    # Handle file that are equal
else
    # Handle files that are different
fi

The diff utility is for inspecting differences between files, while cmp is much better suited for just simply testing if files are different (in a script, for example).

For more specialized cases there is the comm utility that compares lines in sorted files.

edited Jun 22, 2016 at 7:46

answered May 31, 2015 at 15:50

Kusalananda

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3 Comments

laker02 Over a year ago

Sorry i forgot the last part of the code i've edited it now !

Kusalananda Over a year ago

Uh, why? That's a strange requirement.

Kusalananda Over a year ago

cmp is much more efficient than diff. I would say use diff when you want to see the difference in a nicely formatted way, but use cmp if you just want to compare for equality.

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