In zsh, an unquoted word starting with = is replaced by the path of a command

Fact

With the EQUALS option, which is on by default, zsh expands =name at the start of a word to the full path of the command name: echo =ls prints /bin/ls. So a separator such as echo ===== looks up a command called ==== and aborts the line with zsh: ==== not found. bash prints the equals signs.

Why it matters

Scripts and one-liners written against bash fail under zsh, the default shell on macOS, as soon as they print a banner (echo ======) or pass a bare =value argument, and the error names neither the option nor the expansion. Output printed after the failing echo in the same && chain never appears.

How to apply

• Quote such words: echo '=====', printf '%s\n' '=value'.
• In zsh scripts that must pass =word arguments unquoted, setopt no_equals.
• A not found naming a string of = signs is this expansion, not a missing program. See also [[unquoted-url-fails-in-zsh]].