Strings

Basic

Single or multi-line - nothing special needed like in other languages.

X='Hello,
world'

echo $X

Output:

Hello,
world

Double quotes to evaluate.

X="Hello,
$(whoami)"

echo $X

Output:

Hello,
mcurrin

Heredoc

See guide.

Bash supports a _heredoc.

This term appears in other languages like PHP and is a more powerful way of writing a multi-line string.

The equivalent in JS is backtick string.

var x = `\
Line 1
Line 2
${foo}
`

x = f"""\
Line 1
Line 2
{foo}
"""

In the shell, for most cases I find using single or double quotes for a multi-line string works great. But the heredoc does have the advantage that you can use single and double quotes inside the string without escaping them, as your string terminator will be EOF for example. See below.

Note you can use anything but EOF is the common term to start and end the shell heredoc.

Evaluate

cat << EOF

Example:

cat << EOF
Line 1
Line 2
You are $(whoami)
EOF

Output:

Line 1
Line 2
You are mcurrin

Works with cat but not echo.

You can use anything at the start and end but EOF for “end of file” is the convention.

Literal

Prevent evaluation by using quotes. cat << "EOF"

Example:

cat <<- "EOF"
Line 1
Line 2
You are $(whoami)
EOF

Output:

Line 1
Line 2
You are $(whoami)

Indent

From guide

The heredoc becomes more useful than a plain string when you use remove common indentation.

Here we indent the text with tab (not spaces) and also use <<-.

if true; then
		cat <<- EOF
		Line 1
		Line 2
		EOF
fi

Output:

Line 1
Line 2

Note that EOF must not be indented.

Piping

cat <<'EOF' |  sed 's/l/e/g'
Hello
world
EOF

Output:

Heeeo
wored

Write to file.

cat <<'EOF' |  sed 's/l/e/g' > file.txt
Hello
world
EOF