If you are a user who often deals with terminals, you must have noticed that the output ends a line with a highlighted percent symbol on occasion with a variety of applications. Maybe you would think it was because the output was cancelled early (ctrl+c, for example) or something similar, but it doesn’t seem to do this in bash, just do in zsh/fish.
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This happens because it is a “partial line”. The specific feature of zsh (and now fish as well) to let you clearly see unterminated lines in a command’s output. And by default zsh goes to the next line to avoid covering it with the prompt.
When a partial line is preserved, by default you will see an inverse+bold character at the end of the partial line: a “%” for a normal user or a “#” for root. If set, the shell parameter PROMPT_EOL_MARK can be used to customize how the end of partial lines are shown.
In traditional shells (e.g. sh/bash), if a command outputs some data after the last newline character, or, in other words, if it leaves the terminal cursor not at the start of the line, the next prompt by the shell ends up appended to that last unterminated line.
Let’s do the test by using the following commands in zsh and bash respectively:
$ echo -n -e "This is a partial line."
$ echo -n -e "This is a partial line.\n"
echo program options:
-n- Do not output the trailing newline
-e- Enable interpretation of backslash escapes
-E- Disable interpretation of backslash escapes (default)
You will see below result: