942d2a952d
This hard-binds ed to the filesystem (I liked the idea of working only with blockdevs though...), but this is necessary for the upcoming `w` command. We need some kind of way to tell the destination to write to truncate itself. This only has a meaning in the filesystem, but it's necessary to let the file know that its registered file size has possibly shrunk. I thought of alternatives that would have allowed me to keep ed blkdev-centered, but they were all too hackish to my own taste. Hence, this new hard-bind on files. |
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|---|---|---|
| .. | ||
| buf.asm | ||
| cmd.asm | ||
| glue.asm | ||
| io.asm | ||
| main.asm | ||
| README.md | ||
ed - line editor
Collapse OS's ed is modeled after UNIX's ed (let's call it Ued). The goal
is to have an editor that is tight on resources and that doesn't require
ncurses-like screen management.
In general, we try to follow Ued's conventions and the "Usage" section is
mostly a repeat of Ued's man page.
Differences
There are a couple of differences with Ued that are intentional. Differences
not listed here are either bugs or simply aren't implemented yet.
- Always has a prompt,
:. - No size printing on load
- Initial line is the first one
- Line input is for one line at once. Less scriptable for
Ued, but we can't scriptedin Collapse OS anyway... - For the sake of code simplicity, some commands that make no sense are
accepted. For example,
1,2ais the same as2a.
Usage
ed is invoked from the shell with a single argument: the name of the file to
edit. If the file doesn't exist, ed errors out. If it exists, a prompt is
shown.
In normal mode, ed waits for a command and executes it. If the command is
invalid, a line with ? is printed and ed goes back to waiting for a command.
A command can be invalid because it is unknown, malformed or if its address range is out of bounds.
Commands
(addrs)p: Print lines specified inaddrsrange. This is the default command. If only(addrs)is specified, it has the same effect.(addrs)d: Delete lines specified inaddrsrange.(addr)a: Appends a line afteraddr.(addr)i: Insert a line beforeaddr.q: quited
Current line
The current line is central to ed. Address ranges can be expressed relatively
to it and makes the app much more usable. The current line starts at 1 and
every command changes the current line to the last line that the command
affects. For example, 42p changes the current line to 42, 3,7d, to 7.
Addresses
An "address" is a line number. The first line is 1. An address range is a
start line and a stop line, expressed as start,stop. For example, 2,4 refer
to lines 2, 3 and 4.
When expressing ranges, stop can be omitted. It will then have the same value
as start. 42 is equivalent to 42,42.
Addresses can be expressed relatively to the current line with + and -.
+3 means "current line + 3", -5, +2 means "address range starting at 5
lines before current line and ending 2 lines after it`.
+ alone means +1, - means -1.