linux - 我不清楚一个重定向运算符，那就是 <<

Question

<<的用法我不清楚，谁能用一个简单的例子解释一下？真的很感激。

Answer 1

cat <<'EOF'
hello $$
I'm a here document that doesn't interpolate
any $-variables because of the qutoes around
the EOF marker
EOF

echo -------

cat <<EOF
hello $$
I'm a here document that does interpolate
EOF

echo -------

cat <<x
It doesn't matter what you use as the end of file marker
x

echo -------

cat <<'x'
Quotes prevent $-interpolation
x

输出:

hello $$
I'm a here document that doesn't interpolate
any $-variables because of the qutoes around
the EOF marker
-------
hello 29843
I'm a here document that does interpolate
-------
It doesn't matter what you use as the end of file marker
-------
Quotes prevent $-interpolation