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Clavin June
Clavin June

Posted on • Originally published at clavinjune.dev on

Unix Heredoc Cheatsheet

#unix #linux #shell #beginners

Photo by @kellysikkema on Unsplash

Syntax 

[cmd] <<[-] delimeter [cmd]
    contents
delimeter
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All contents will be passed to the cmd as an input, examples below will use EOF as a delimeter and cat as a command, you can change to whatever you want.

With Variable 

cat <<EOF
    echo "$HOME"
EOF
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result:

    echo "/home/clavinjune"
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Escape Variable

Use \$ instead of $ to escape specific variable

cat <<EOF
    echo "$HOME"
    echo "\$HOME"
EOF
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result:

    echo "/home/clavinjune"
    echo "$HOME"
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Escape All Variables

Use 'EOF' instead of EOF to escape all variables

cat <<'EOF'
    echo "$HOME"
    echo "\$HOME"
EOF
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result:

    echo "$HOME"
    echo "\$HOME"
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Remove Leading Tab

Use <<- instead of << to remove leading tabs

cat <<-EOF
    echo "$HOME"
    echo "\$HOME"
EOF
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result:

echo "/home/clavinjune"
echo "$HOME"
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Add More Pipeline 

cat <<EOF | grep june
    echo "$HOME"
    echo "\$HOME"
EOF
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result:

    echo "/home/clavinjune"
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Write To a File 

cat <<-'EOF' > /tmp/foo
    echo "$HOME"
    echo "\$HOME"
EOF
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result:

$ cat /tmp/foo 
echo "$HOME"
echo "\$HOME"
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Thank you for reading!

Top comments (1)

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andywu1998 profile image
andywu1998 •

so nice, thanks for sharing. expect to update~

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