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bash scripts

heredoc

A Here document (Heredoc) is a redirection that allows you to pass multiple lines of input to a command.

By default the contents of the heredoc are evaluated as if it were a double quoted string. To avoid evaluation, and treat special characters as literals, surround the here word with single quotes, eg:

cat <<'EOF'
               ((`\
            ___ \\ '--._
         .'`   `'    o  )
        /    \   '. __.'
       _|    /_  \ \_\_
jgs   {_\______\-'\__\_\
EOF

<<- ignores leading tabs.

To read into a variable:

read -r -d '' VAR << EOM
This is line 1.
This is line 2.
Line 3.
EOM

https://en.wikipedia.org/wiki/Here_document#Unix_shells https://stackoverflow.com/a/2500451/149412

detect interactive shell

[[ $- == *i* ]] && echo "in an interactive shell"

script dir

to get the current script dir:

"$(dirname "$(readlink -f "${BASH_SOURCE[0]:-$0}")")"

readlink converts a relative to absolute and resolves symlinks. It's similar to realpath but more ubiquitous eg: realpath doesn't ship in BSD (Darwin) whereas readlink ships in both BSD and Linux.

dirname extracts the directory part of the path.

works in both bash and zsh, either sourced or directly run:

how bash zsh
direct uses BASH_SOURCE[0] uses BASH_SOURCE[0]
sourced uses BASH_SOURCE[0] uses $0