Question

This is a small question I know. We are writing a Bash highlighter in Ruby and need to implement heredoc highlighting. The two formats I have seen are this. Note the space before the EOF

cat <<EOF
Hello
World
EOF

cat << EOF
Hello
World
EOF

The question is, is it incorrect/unofficial/bad practice to use a space before the first EOF?

• gnu.org/software/bash/manual/bashref
• linux.die.net/man/1/bash
• tldp.org/LDP/abs/html/here-docs.html
• wikipedia.org/wiki/Here_document

Answer 1

The POSIX Shell Command Language specification explicitly specifies that the file-descriptor number, if any, “immediately precede the redirection operator”; but it makes no similar requirement that the redirection operator immediately precede the word. The token recognition rules imply that any spaces would be discarded between the redirection operator and the word, so I think that any correct implementation should accept such spaces. (Admittedly, this would be more reassuring if it weren’t that the same token recognition rules imply the same thing about spaces between the file-descriptor number and the redirection operator.)

Although the Bash Reference Manual‘s examples for heredocs don’t include a space before the word, it does give other examples with redirections that do include a space before the word, and nothing in either the POSIX spec or the Bash Reference Manual gives any reason to think of heredocs’ word as being different in this respect from the word in any other kind of redirection, so I don’t think it should be thought of as bad practice. I think your syntax-highlighter should support both, unless one of the goals of the project is to enforce some sort of standard style for such things.