Ed Editor

Ed Editor

cupid-os includes a faithful implementation of the classic Unix ed(1) line editor, written entirely in CupidC. Ed operates in-memory and can read/write files through the VFS (both ramfs and FAT16 disk).

Implementation

Ed is implemented as a CupidC program at bin/ed.cc. It is automatically embedded into the kernel image at build time and is available as /bin/ed.cc in the in-memory filesystem. When you type ed at the shell prompt, the auto-discovery system finds /bin/ed.cc and JIT-compiles it.

Source: bin/ed.cc (~900 lines of CupidC)

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Starting Ed

> ed                    # Start with empty buffer
> ed LICENSE.txt        # Open file from in-memory filesystem
> ed README.TXT         # Open file from FAT16 disk

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Quick Start

Create a File

> ed
a                       # Enter append mode
Hello, CupidOS!
This is my first file.
Line three.
.                       # End input mode (dot on its own line)
w myfile.txt            # Write to disk (prints byte count)
48
q                       # Quit

Edit an Existing File

> ed myfile.txt
3                       # Print line count (shows "3")
1,3p                    # Print lines 1–3
Hello, CupidOS!
This is my first file.
Line three.
2s/first/second/        # Substitute on line 2
2p                      # Verify
This is my second file.
w                       # Save
q                       # Quit

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Modes

Ed has two modes:

1. Command mode (default) - Enter commands to navigate, edit, display, and save
2. Input mode - Enter text line by line; exit by typing . alone on a line

Commands that enter input mode: a (append), i (insert), c (change).

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Address Forms

Most commands accept an address or address range to specify which lines to operate on.

Address	Meaning
3	Line 3
.	Current line
$	Last line
+ / -	Relative to current line
+3 / -2	Offset from current line
/pattern/	Next line matching pattern (forward search)
?pattern?	Previous line matching pattern (backward search)
'x	Line marked with kx
%	All lines (shorthand for 1,$)
1,5	Lines 1 through 5
3,	Line 3 through current
,7	Current through line 7

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Commands

Display

Command	Description
p	Print current line (or addressed lines)
n	Print with line numbers
l	Print with escape characters visible
=	Print number of lines in buffer

Input Mode

Command	Description
a	Append text after addressed line
i	Insert text before addressed line
c	Change (replace) addressed lines

End input mode by typing . on a line by itself.

Editing

Command	Description
d	Delete addressed lines
j	Join addressed lines into one
m <addr>	Move lines to after address
t <addr>	Copy lines to after address
s/pat/repl/	Substitute first match on addressed lines
s/pat/repl/g	Substitute all matches
s/pat/repl/gp	Substitute all and print
u	Undo last change (single level)

File Operations

Command	Description
e <file>	Edit file (replaces buffer, warns if unsaved)
E <file>	Edit file (no warning)
r <file>	Read file and append to buffer
w [file]	Write buffer to file (prints byte count)
wq	Write and quit
W [file]	Append buffer to file
f [name]	Get or set current filename

Files are read and written through the VFS layer, supporting both the in-memory filesystem (ramfs) and FAT16 disk.

Search

Command	Description
/pattern/	Search forward for pattern
?pattern?	Search backward for pattern

Global Commands

Command	Description
g/RE/cmd	Execute command on all lines matching regex
v/RE/cmd	Execute command on all lines NOT matching regex

Other

Command	Description
k<x>	Mark current line with letter x (a–z)
H	Toggle verbose error messages
h	Show last error message
q	Quit (warns if unsaved)
Q	Quit (no warning)

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Regex

Ed supports basic regular expressions:

Pattern	Meaning
.	Any single character
*	Zero or more of the preceding character
^	Anchor to start of line
$	Anchor to end of line
literal	Matches itself

Examples

/hello/           # Find next line containing "hello"
?error?           # Find previous line containing "error"
s/^/    /         # Indent current line (add 4 spaces)
s/world/CupidOS/  # Replace "world" with "CupidOS"
g/TODO/p          # Print all lines containing "TODO"
v/^#/d            # Delete all lines NOT starting with #

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Example Session: Creating a CupidScript

> ed
a
#!/bin/cupid
# A simple counter script
COUNT=0
while [ $COUNT -lt 5 ]; do
    echo "Count: $COUNT"
    COUNT=$((COUNT + 1))
done
echo "Done!"
.
1,9n
1	#!/bin/cupid
2	# A simple counter script
3	COUNT=0
4	while [ $COUNT -lt 5 ]; do
5	    echo "Count: $COUNT"
6	    COUNT=$((COUNT + 1))
7	done
8	echo "Done!"
w counter.cup
98
q
> cupid counter.cup
Count: 0
Count: 1
Count: 2
Count: 3
Count: 4
Done!

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Limits

Limit	Value
Maximum lines	1024
Maximum line length	256 characters
Undo levels	1 (single undo)
Marks	26 (a–z)

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See Also

• CupidScript - Write scripts to run with cupid
• Shell Commands - All shell commands including ed
• Filesystem - File I/O and FAT16 details