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70 lines
2.6 KiB
Markdown
70 lines
2.6 KiB
Markdown
# ed - line editor
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Collapse OS's `ed` is modeled after UNIX's ed (let's call it `Ued`). The goal
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is to have an editor that is tight on resources and that doesn't require
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ncurses-like screen management.
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In general, we try to follow `Ued`'s conventions and the "Usage" section is
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mostly a repeat of `Ued`'s man page.
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## Differences
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There are a couple of differences with `Ued` that are intentional. Differences
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not listed here are either bugs or simply aren't implemented yet.
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* Always has a prompt, `:`.
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* No size printing on load
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* Initial line is the first one
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* Line input is for one line at once. Less scriptable for `Ued`, but we can't
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script `ed` in Collapse OS anyway...
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* For the sake of code simplicity, some commands that make no sense are
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accepted. For example, `1,2a` is the same as `2a`.
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## Usage
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`ed` is invoked from the shell with a single argument: the name of the file to
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edit. If the file doesn't exist, `ed` errors out. If it exists, a prompt is
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shown.
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In normal mode, `ed` waits for a command and executes it. If the command is
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invalid, a line with `?` is printed and `ed` goes back to waiting for a command.
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A command can be invalid because it is unknown, malformed or if its address
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range is out of bounds.
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### Commands
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* `(addrs)p`: Print lines specified in `addrs` range. This is the default
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command. If only `(addrs)` is specified, it has the same effect.
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* `(addrs)d`: Delete lines specified in `addrs` range.
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* `(addr)a`: Appends a line after `addr`.
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* `(addr)i`: Insert a line before `addr`.
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* `w`: write to file. For now, `q` is implied in `w`.
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* `q`: quit `ed` without writing to file.
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### Current line
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The current line is central to `ed`. Address ranges can be expressed relatively
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to it and makes the app much more usable. The current line starts at `1` and
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every command changes the current line to the last line that the command
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affects. For example, `42p` changes the current line to `42`, `3,7d`, to 7.
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### Addresses
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An "address" is a line number. The first line is `1`. An address range is a
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start line and a stop line, expressed as `start,stop`. For example, `2,4` refer
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to lines 2, 3 and 4.
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When expressing ranges, `stop` can be omitted. It will then have the same value
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as `start`. `42` is equivalent to `42,42`.
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Addresses can be expressed relatively to the current line with `+` and `-`.
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`+3` means "current line + 3", `-5, +2` means "address range starting at 5
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lines before current line and ending 2 lines after it`.
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`+` alone means `+1`, `-` means `-1`.
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`.` means current line. It can usually be omitted. `p` is the same as `.p`.
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`$` means the last line of the buffer.
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