How can I concat results in the here document?

Question

I have this script:

while read $item;
do
    # Some bash logic here
done <<< "$({ cat /path/to/some/file; echo; })"

Now I want to also use find to find the name of some directories, and pass that alongside the cat to the while loop.

In other words, I want to:

• cat a file
• find some directories
• Concatenate the results
• Feed them as here-document to the while loop

I'm stuck at this point.

I though of duplicating the while logic, which is not a good method. I also thought of reusing the logic inside the while loop using functions.

However, concatenating stuff in here-document might seem to be the correct way to do it.

Answer 1

Actually <<< "$({ cat /path/to/some/file; echo; })" is a here-string containing a quoted command substitution rather than a here-document. As Kamil Maciorowski has already pointed out, you already know how to concatenate the results of the two commands cat /path/to/some/file and echo inside the command substitution, and you could do the same with cat and find:

... <<< "$(cat /path/to/some/file; find . -name '*foo*')"

I omitted the inner { ... } since the commands are already grouped by $( ... ).

However it would be more natural IMHO to use process substitution to concatenate the outputs. To see how that works, start from simple input redirection

while IFS= read -r item
do
    # Some bash logic here
done < /path/to/some/file

which redirects the contents of the file to the loop via stdin; then

while IFS= read -r item
do
    # Some bash logic here
done < <(cat /path/to/some/file)

which converts the output of cat /path/to/some/file to a pseudo-file that you can redirect in the same way. Now it's a simple matter to add another stdout-generating command to the process list:

while IFS= read -r item
do
    # Some bash logic here
done < <(cat /path/to/some/file; find . -name '*foo*')

See for example

• What is more efficient or recommended for reading output of a command into variables in Bash?

• Why does a Bash 'while' read loop with a command substitution herestring not read the entire input?

Note that in all cases, the syntax is read item not read $item.