read gets skipped in here-document

Question

I have a script test1.sh. It has rwx permissions for all users. It contains this text :

echo "You are in test1.sh"
read -p "Enter some text : " text1
echo "You entered : $text1"
bash <<!
        echo "You are now in a here-document"
        read -p "Enter some more text : " text2
        echo "You also entered : $text2"
        echo "End of the here-document"
!
echo "End of test1.sh"

When I run it as sh test1.sh, the second read statement is skipped completely. Here is the output :

$ sh test1.sh
You are in test1.sh
Enter some text : hello
You entered : hello
You are now in a here-document
End of the here-document
End of test1.sh

When I run it as ./test1.sh, both statements are skipped.

$ ./test1.sh
You are in test1.sh
./test1.sh[11]: read: no query process
You entered :
You are now in a here-document
End of the here-document
End of test1.sh

If I change test1.sh to use /dev/tty,

echo "You are in test1.sh"
read -p "Enter some text : " text1
echo "You entered : $text1"
bash <<!
        echo "You are now in a here-document" > /dev/tty
        read -p "Enter some more text : " text2 < /dev/tty
        echo "You also entered : $text2" > /dev/tty
        echo "End of the here-document" > /dev/tty
!
echo "End of test1.sh"

then I get :

$ sh test1.sh
You are in test1.sh
Enter some text : hello
You entered : hello
You are now in a here-document
Enter some more text : bye
You also entered :
End of the here-document
End of test1.sh

The second text didn't get printed.

If I edit the file to use stdin and stdout,

echo "You are in test1.sh"
read -p "Enter some text : " text1
echo "You entered : $text1"
bash <<!
        echo "You are now in a here-document" > /dev/stdout
        read -p "Enter some more text : " text2 < /dev/stdin
        echo "You also entered : $text2" > /dev/stdout
        echo "End of the here-document" > /dev/stdout
!
echo "End of test1.sh"

, I get this output :

$ sh test1.sh
You are in test1.sh
Enter some text : hello
You entered : hello
You are now in a here-document
You also entered :
End of the here-document
End of test1.sh

I couldn't input any text for the second read statement

I want to read input from each read statement into text1 and text2 respectively and I want both $text1 and $text2 to be echo-ed. Could you please tell me what is wrong?

Answer 1

When you're processing the here-document, standard input is the rest of the here-document. So in the first script, the second read line is reading the echo line that comes after it. Since that line is being read by read , it doesn't get executed by the shell.

I think the reason for the error in your second script is because you didn't put #!/bin/bash at the beginning of the script. Without that, the script is executed by sh instead of bash , and it doesn't understand the -p option to read .

In the third script, the reason $text2 doesn't get echoed is because variables in a here-document are expanded by the shell reading the here-document. But the variable $text2 is set in the child shell process. You can solve this with <<'!' -- putting quotes around the end-marker means that the here-document should be treated as a literal string, and variables should not be expanded.

In the last script, redirecting input from /dev/stdin doesn't do anything, because that's where input is already coming from.

Answer 2

Consider the first script:

echo "You are in test1.sh"
read -p "Enter some text : " text1
echo "You entered : $text1"
bash <<!
        echo "You are now in a here-document"
        read -p "Enter some more text : " text2
        echo "You also entered : $text2"
        echo "End of the here-document"
!
echo "End of test1.sh"

Where is the standard input of the bash coming from? Answer: the here document. So the read tries to read from standard input too. The chances are that the shell has read everything so the read comes up empty.