How to Use a Heredoc Inside a Bash Function: Syntax and Examples

Many developers encounter issues when trying to use a heredoc inside a Bash function. The error message often looks like this:

./script.sh: line X: Syntax error: end of file unexpected (expecting "}")

The issue typically occurs when:

Using #!/bin/sh instead of #!/bin/bash
Improper indentation in the heredoc block
Missing or incorrect heredoc delimiter

Here's the proper way to use a heredoc in a Bash function:

#!/bin/bash

my_function() {
    cat <<'HEREDOC'
This is the heredoc content
It can span multiple lines
HEREDOC
}

my_function

Always use #!/bin/bash shebang for Bash-specific features
The closing delimiter (HEREDOC in this case) must be at the beginning of the line
Quoting the delimiter (<<'HEREDOC') prevents variable expansion

Example with variable substitution:

#!/bin/bash

generate_report() {
    local user=$1
    cat <


Example with indented heredoc (Bash 4+):
#!/bin/bash

indented_output() {
    local prefix="    "
    cat <<-INDENTED
    ${prefix}This line is indented
    ${prefix}So is this one
INDENTED
}

indented_output


Check for hidden whitespace characters after the delimiter
Ensure your script uses Unix line endings (LF) if developed on Windows
Verify Bash version with bash --version


When implementing heredocs in bash functions, the most common error occurs due to incorrect shell interpreter declaration. Your script uses #!/bin/sh which may point to dash (not bash) on Ubuntu systems.
#!/bin/bash
# Always use bash for advanced features

my_function() {
    cat <<HEREDOC
This is proper heredoc content
- Supports parameter expansion
- Preserves indentations
HEREDOC
}

For clean code formatting while maintaining functionality:
#!/bin/bash

indented_heredoc() {
    # Using <<- to strip leading tabs (not spaces)
    cat <<-END
        This line has tabs
        $USER can see variables
        END  # Must be at line start with tab
}

#!/bin/bash

# 1. Variable substitution
dynamic_heredoc() {
    local greeting="Hello"
    cat <<MSG
${greeting}, $USER!
Today is $(date)
MSG
}

# 2. Passing to commands
pipe_example() {
    grep "important" <<CONFIG
server_ip=192.168.1.1
important_flag=true
backup_dir=/var/log
CONFIG
}


Unexpected EOF: Ensure closing delimiter is at line start with no trailing spaces
Parameter expansion fails: Use double quotes or escape special chars
Indent problems: For stripped indents, use <<- and tabs only