bashheredoc

How can I write a heredoc to a file in Bash script?


How can I write a here document to a file in Bash script?


Solution

  • Read the Advanced Bash-Scripting Guide Chapter 19. Here Documents.

    Here's an example which will write the contents to a file at /tmp/yourfilehere

    cat << EOF > /tmp/yourfilehere
    These contents will be written to the file.
            This line is indented.
    EOF
    

    Note that the final 'EOF' (The LimitString) should not have any whitespace in front of the word, because it means that the LimitString will not be recognized.

    In a shell script, you may want to use indentation to make the code readable, however this can have the undesirable effect of indenting the text within your here document. In this case, use <<- (followed by a dash) to disable leading tabs (Note that to test this you will need to replace the leading whitespace with a tab character, since I cannot print actual tab characters here.)

    #!/usr/bin/env bash
    
    if true ; then
        cat <<- EOF > /tmp/yourfilehere
        The leading tab is ignored.
        EOF
    fi
    

    If you don't want to interpret variables in the text, then use single quotes:

    cat << 'EOF' > /tmp/yourfilehere
    The variable $FOO will not be interpreted.
    EOF
    

    To pipe the heredoc through a command pipeline:

    cat <<'EOF' |  sed 's/a/b/'
    foo
    bar
    baz
    EOF
    

    Output:

    foo
    bbr
    bbz
    

    ... or to write the the heredoc to a file using sudo:

    cat <<'EOF' |  sed 's/a/b/' | sudo tee /etc/config_file.conf
    foo
    bar
    baz
    EOF