Inside a script you want to feed several lines of text that are written directly in the script, ending at a marker word, to a command's standard input. Which redirection operator introduces that construct?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
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The options
Not correct >>
Wrong. >> is output redirection that appends to a file. It concerns standard output, not standard input.
Not correct <<<
Wrong for multiple lines. <<< is a here-string, which feeds one single string to standard input, as in `grep root <<< "$line"`.
Not correct <
Wrong. < redirects standard input from an existing FILE; it cannot take text written inline in the script.
Correct <<
Correct. << starts a here-document: everything up to the line containing the delimiter word becomes the command's standard input.
Why
A here-document looks like `cat <<EOF` followed by the text and a line containing only EOF. Variables and command substitution are expanded inside it unless you quote the delimiter (<<'EOF'), and the <<- variant lets you indent both the body and the closing delimiter with TAB characters. The related <<< is a here-string for a single line.
Where this comes from
- Cited
- LPI exam objective 103.4
- What it says
- Use here-documents to supply inline text as standard input.
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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