bash Reading array from file

Question

I've already read a lot of questions concerning reading and writing in ARRAY in bash. I could not find the solution to my issue.

Actually, I've got a file that contains the path of a lot of files.

cat MyFile
> ~/toto/file1.txt
> ~/toto/file2.txt
> ~/toto/file3.txt
> ~/toto/file4.txt
> ~/toto/file5.txt

I fill an array ARRAY to contain this list:

readarray ARRAY < MyFile.txt

or

while IFS= read -r line
do 
   printf 'TOTO %s\n' "$line"
   ARRAY+=("${line}")
done <MyFile.txt

or

for line in $(cat ${MyFile.txt}) ; 
    do echo "==> $line"; 
    ARRAY+=($line) ; 
done

All those methods work well to fill the ARRAY,

echo "0: ${ARRAY[1]}"
echo "1: ${ARRAY[2]}"
> 0: ~/toto/file1.txt
> 1: ~/toto/file2.txt

This is awesome. but my problem is that if I try to diff the content of the file it does not work, it looks like the it does not expand the content of the file

diff ${ARRAY[1]} ${ARRAY[2]}
diff: ~/toto/file1.txt: No such file or directory
diff: ~/toto/file2.txt: No such file or directory

but when a print the content: echo diff ${ARRAY[1]} ${ARRAY[2]}

diff ~/toto/file1.txt ~/toto/file2.txt

and execute it I get the expected diff in the file diff ~/toto/file1.txt ~/toto/file2.txt

 3c3
 < Param = {'AAA', 'BBB'}
 ---
 > Param = {'AAA', 'CCC'}

whereas if I fill ARRAY manually this way:

ARRAY=(~/toto/file1.txt ~/toto/file2.txt)

diff works well.

Does anyone have an idea? Thanks a lot Regards, Thomas

Nic3500 · Accepted Answer · 2019-10-16 11:37:37Z

1

Tilde expansion does not happen when you use variable substitution from ${ARRAY[index]}.

Put the full path to the files in MyFile.txt and run your code again.

edited Oct 16, 2019 at 11:37

answered Oct 14, 2019 at 17:28

Nic3500

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5 Comments

janos Over a year ago

I don't think how Cyrus' solution can work, because I don't think the ~ in variables will get expanded.

Nic3500 Over a year ago

Actually it works, if you do not put the " around the ${ARRAY[INDEX]} variable subsititution. So diff <(cat ${ARRAY[0]}) <(cat ${ARRAY[1]}). That is because readarray does not remove the \n characters at the end of each line.

janos Over a year ago

No, ~ is not expanded, and I think your reasoning about \n is false too ;-)

Nic3500 Over a year ago

Well try it, I am not reasoning, I experiment and deduce. with the ", I clearly see the \n character. Without it, there are no \n. Or propose a more general solution. GNU bash, version 4.4.20(1)-release (x86_64-pc-linux-gnu)

janos Over a year ago

The flaw in the reasoning is that \n being there will not cause tilde expansion. So Cyrus' solution cannot work, as long as ~ is in a variable. I would drop your sentence about Cyrus' solution. The rest of the answer (the first sentence and the last sentence) is good.

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