bash testing

Prefer [[ (extended test command) to [ because [[ supports regex and substring matching and has better error handling.

EG:

    if [ $(cmd that errors with no std out) != 200 ]; then
      ...
    fi

Will produce a message [: !=: unary operator expected but the script will still complete successfully.

    if [[ $(cmd that errors with no std out)  != 200 ]]; then
      ...
    fi

Will raise and error and stop.

[[ is only available in bash and zsh.

Examples

[[ -z "$query_execution" ]] True if the length of string is zero. [[ -n "$sql" ]] True if the length of string is nonzero.