Table of Contents

2.1 Introduction to ED

2.1.1 ED Operation
2.1.2 Text Transfer Functions
2.1.3 Memory Buffer Organization
2.1.4 Line Numbers and ED Start Up
2.1.5 Memory Buffer Operations
2.1.6 Command Strings
2.1.7 Text Search and Alteration
2.1.8 Source Libraries
2.1.9 Repetitive Command Execution

Tables

2-1 ED Text Transfer Commands
2-2 Editing Commands
2-3 Line-editing Controls
2-4 Error Message Symbols
2-5 ED Control Characters
2-6 ED Commands

Figures

2-1 Overall ED Operation
2-2 Memory Buffer Organization
2-3 Logical Organization of the Memory Buffer

2.1 Introduction to ED

ED is the context editor for CP/M, and is used to create and alter CP/M source files. To start ED, type a command of the following form:

     ED filename

or

     ED filename.typ

Generally, ED reads segments of the source file given by filename or filename.typ into the central memory, where you edit the file and it is subsequently written back to disk after alterations. If the source file does not exist before editing, it is created by ED and initialized to empty. The overall operation of ED is shown in Figure 2-1.

2.1.1 ED Operation

ED operates upon the source file, shown in Figure 2-1 by x.y, and passes all text through a memory buffer where the text can be viewed or altered. The number of lines that can be maintained in the memory buffer varies with the line length, but has a total capacity of about 5000 characters in a 20K CP/M system.

Edited text material is written into a temporary work file under your command. Upon termination of the edit, the memory buffer is written to the temporary file, followed by any remaining (unread) text in the source file. The name of the original file is changed from x.y to x.BAK so that the most recent edited source file can be reclaimed if necessary. See the CP/M commands ERASE and RENAME. The temporary file is then changed from x.$$$ to x.y, which becomes the resulting edited file.

Figure 2-1. Overall ED Operation

The memory buffer is logically between the source file and working file, as shown in Figure 2-2.

Figure 2-2. Memory Buffer Organization

2.1.2 Text Transfer Functions

Given that n is an integer value in the range 0 through 65535, several single-letter ED commands transfer lines of text from the source file through the memory buffer to the temporary (and eventually final) file. Single letter commands are shown in upper-case, but can be typed in either upper- or lower-case.

There are a number of special cases to consider. If the integer n is omitted in any ED command where an integer is allowed, then 1 is assumed. Thus, the commands A and W append one line and write one line, respectively. In addition, if a pound sign # is given in the place of n, then the integer 65535 is assumed (the largest value for n that is allowed). Because most source files can be contained entirely in the memory buffer, the command #A is often issued at the beginning of the edit to read the entire source file to memory. Similarly, the command #W writes the entire buffer to the temporary file.

Two special forms of the A and W commands are provided as a convenience. The command OA fills the current memory buffer at least half full, while OW writes lines until the buffer is at least half empty. An error is issued if the memory buffer size is exceeded. You can then enter any command, such as W, that does not increase memory requirements. The remainder of any partial line read during the overflow will be brought into memory on the next successful append.

2.1.3 Memory Buffer Organization

The memory buffer can be considered a sequence of source lines brought in with the A command from a source file. The memory buffer has an imaginary character pointer (CP) that moves throughout the memory buffer under command of the operator.

The memory buffer appears logically as shown in Figure 2-3, where the dashes represent characters of the source line of indefinite length, terminated by carriage return (<cr>) and line-feed (<If>) characters, and CP represents the imaginary character pointer. Note that the CP is always located ahead of the first character of the first line, behind the last character of the last line, or between two characters. The current line CL is the source line that contains the CP.

Figure 2-3. Logical Organization of Memory Buffer

2.1.4 Line Numbers and ED Start-up

ED produces absolute line number prefixes that are used to reference a line or range of lines. The absolute line number is displayed at the beginning of each line when ED is in insert mode (see the I command in Section 2.1.5). Each line number takes the form

     nnnnn:

where nnnnn is an absolute line number in the range of 1 to 65535. If the memory buffer is empty or if the current line is at the end of the memory buffer, nnnnn appears as 5 blanks.

You can reference an absolute line number by preceding any command by a number followed by a colon, in the same format as the line number display. In this case, the ED program moves the current line reference to the absolute line number, if the line exists in the current memory buffer. The line denoted by the absolute line number must be in the memory buffer (see the A command). Thus, the command

     345:T

is interpreted as move to absolute 345, and type the line. Absolute line numbers are produced only during the editing process and are not recorded with the file. In particular, the line numbers will change following a deleted or expanded section of text.

You can also reference an absolute line number as a backward or forward distance from the current line by preceding the absolute number by a colon. Thus, the command

     :400T

is interpreted as type from the current line number through the line whose absolute number is 400. Combining the two line reference forms, the command

     345::400T

is interpreted as move to absolute line 345, then type through absolute line 400. Absolute line references of this sort can precede any of the standard ED commands.

Line numbering is controlled by the V (Verify Line Numbers) command. Line numbering can be turned off by typing the -V command.

If the file to edit does not exist, ED displays the following message:

     NEW FILE

To move text into the memory buffer, you must enter an i command before typing input lines and terminate each line with a carriage return. A single CTRL-Z character returns ED to command mode.

2.1.5 Memory Buffer Operation

When ED begins, the memory buffer is empty. You can either append lines from the source file with the A command, or enter the lines directly from the console with the insert command. The insert command takes the following form:

     I

ED then accepts any number of input lines. You must terminate each line with a <cr> (the <If> is supplied automatically). A single CTRL-Z, denoted by an up arrow (T)Z, returns ED to command mode. The CP is positioned after the last character entered. The following sequence:

     I<cr>
     NOW IS THE<cr>
     TIME FOR<cr>
     ALL GOOD MEN<cr>
     ^Z

leaves the memory buffer as

     NOW IS THE<cr><lf>
     TIME FOR<cr><lf>
     ALL GOOD MEN<cr><lf>

Generally, ED accepts command letters in upper- or lower-case. If the command is upper-case, all input values associated with the command are translated to upper-case. If the I command is typed, all input lines are automatically translated internally to upper-case. The lower-case form of the i command is most often used to allow both upper- and lower-case letters to be entered.

Various commands can be issued that control the CP or display source text in the vicinity of the CP. The commands shown below with a preceding n indicate that an optional unsigned value can be specified. When preceded by +-, the command can be unsigned, or have an optional preceding plus or minus sign. As before, the pound sign # is replaced by 65535. If an integer n is optional, but not supplied, then n=1 is assumed. Finally, if a plus sign is optional, but none is specified, then + is assumed.

2.1.6 Command Strings

Any number of commands can be typed contiguously (up to the capacity of the console buffer) and are executed only after you press the <cr>. Table 2-3 summarizes the CP/M console line-editing commands used to control the input command line.

Suppose the memory buffer contains the characters shown in the previous section, with the CP following the last character of the buffer. In the following example, the command strings on the left produce the results shown to the right. Use lower-case command letters to avoid automatic translation of strings to upper-case.

     NOW IS THE
     TIME FOR

     ^NOW IS THE<cr><lf>
     TIME FOR<cr><lf>
     ALL GOOD MEN<cr><lf>

     NOW I^S THE<cr><lf>

     NOW IS THE<cr><lf>
     TIME FOR<cr><lf>
     ^ALL GOOD MEN<cr><lf>

     NOW IS THE<cr><lf>^

     NOW IS THE<cr><lf>
     TIME TO<cr><lf>
     INSERT<cr><lf>^

     NOW IS THE<cr><lf>
     ^TIME TO<cr><lf>
     INSERT<cr><lf>

     NOW IS THE<cr><lf>
     TIME TO<cr><lf>
     ^INSERT<cr><lf>

2.1.7 Text Search and Alteration

ED has a command that locates strings within the memory buffer. The command takes the form

     nFs<cr>

or

     nFs^Z

where s represents the string to match, followed by either a <cr> or CTRL-Z, denoted by ^Z. ED starts at the current position of CP and attempts to match the string. The match is attempted n times and, if successful, the CP is moved directly after the string. If the n matches are not successful, the CP is not moved from its initial position. Search strings can include CTRL-L, which is replaced by the pair of symbols <cr><lf>.

The following commands illustrate the use of the F command:

     ^NOW IS THE<cr><lf>
     TIME FOR<cr><lf>
     ALL GOOD MEN<cr><lf>

     NOW IS T^HE<cr><lf>

     NOW IS THE<cr><lf>
     TI^ME FOR<cr><lf>
     ALL GOOD MEN<cr><lf>

An abbreviated form of the insert command is also allowed, which is often used in conjunction with the F command to make simple textual changes. The form is

     Is^Z

or

     Is<cr>

where s is the string to insert. If the insertion string is terminated by a CTRL-Z, the string is inserted directly following the CP, and the CP is positioned directly after the string. The action is the same if the command is followed by a <cr> except that a <cr><lf> is automatically inserted into the text following the string. The following command sequences are examples of the F and I commands:

     THIS IS ^NOW THE<cr><lf>
     TIME FOR<cr><lf>
     ALL GOOD MEN<cr><lf>

     THIS IS NOW THE<cr><lf>
     PLACE ^FOR<cr><lf>
     ALL GOOD MEN<cr><lf>

     THIS IS NOW THE<cr><lf>
     PLACE FOR<cr><lf>
     ALL CHANGES^<cr><lf>

     THIS IS NOW THE<cr><lf>
     PLACE FOR<cr><lf>
     ALL SOURCE<cr><lf>
     ^CHANGES<cr><lf>

ED also provides a single command that combines the F and I commands to perform simple string substitutions. The command takes the following form:

     nSs1^Zs2<cr>

or

     nSs1^Zs2^Z

and has exactly the same effect as applying the following command string a total of n times:

     Fs1^Z-kDIs2<cr>

or

     Fs1^Z-kDIs2^Z

where k is the length of the string. ED searches the memory buffer starting at the current position of CP and successively substitutes the second string for the first string untill the end of buffer, or until the substitution has been performed n times.

As a convenience, a command similar to F is provided by ED that automatically appends and writes lines as the search proceeds. The form is

     nNs<cr>

or

     nNs^Z

which searches the entire source file for the nth occurrence of the strings (you should recall that F fails if the string cannot be found in the current buffer). The operation of the N command is precisely the same as F except in the case that the string cannot be found within the current memory buffer. In this case, the entire memory content is written (that is, an automatic #W is issued). Input lines are then read until the buffer is at least half full, or the entire source file is exhausted. The search continues in this manner until the string has been found n times, or until the source file has been completely transferred to the temporary file.

A final line editing function, called the Juxtaposition comniand, takes the form

     nJs1^Zs2^Zs3<cr>

or

     nJs1^Zs2^Zs3^Z

with the following action applied n times to the memory buffer: search from the current CP for the next occurrence of the string S1. If found, insert the string S2, and move CP to follow S2. Then delete all characters following CP up to, but not including, the string S3, leaving CP directly after S2. If S3 cannot be found, then no deletion is made. If the current line is

     NOW IS THE TIME<cr><lf>

the command

     JW^ZWHAT^Z^L<cr>

results in

     NOW WHAT<cr><lf>

You should recall that ^L (CTRL-L) represents the pair <cr><lf> in search and substitute strings.

The number of characters ED allows in the F, S, N, and J commands is limited to 100 symbols.

2.1.8 Source Libraries

ED also allows the inclusion of source libraries during the editing process with the R command. The form of this command is

     Rfilename^Z

or

     Rfilename<cr>

where filename is the primary filename of a source file on the disk with an assumed filetype of LIB. ED reads the specified file, and places the characters into the memory buffer after CP, in a manner similar to the I command. Thus, if the command

     RMACRO<cr>

is issued by the operator, ED reads from the file MACRO.LIB until the end-of-file and automatically inserts the characters into the memory buffer.

ED also includes a block move facility implemented through the X (Transfer) command. The form

     nX

transfers the next n lines from the current line to a temporary file called

     X$$$$$$.LIB

which is active only during the editing process. You can reposition the current line reference to any portion of the source file and transfer lines to the temporary file. The transferred lines accumulate one after another in this file and can be retrieved by simply typing

     R

which is the trivial case of the library read command. In this case, the entire transferred set of lines is read into the memory buffer. Note that the X command does not remove the transferred lines from the memory buffer, although a K command can be used directly after the X, and the R command does not empty the transferred LIB file. That is, given that a set of lines has been transferred with the X command, they can be reread any number of times back into the source file. The command

     0X

is provided to empty the transferred line file.

Note that upon normal completion of the ED program through Q or E, the temporary LIB file is removed. If ED is aborted with a CTRL-C, the LIB file will exist if lines have been transferred, but will generally be empty (a subsequent ED invocation will erase the temporary file).

2.1.9 Repetitive Command Execution

The macro command M allows you to group ED commands together for repeated evaluation. The M command takes the following form:

     nMCS<cr>

or

     nMCS^Z

where CS represents a string of ED commands, not including another M command. ED executes the command string n times if n>1. If n=0 or 1, the command string is executed repetitively until an error condition is encountered (for example, the end of the memory buffer is reached with an F command).

As an example, the following macro changes all occurrences of GAMMA to DELTA within the current buffer, and types each line that is changed:

     MFGAMMA^Z-5DIDELTA^Z0TT<cr>

or equivalently

     MSGAMMA^ZDELTA^Z0TT<cr>

2.2 ED Error Conditions

On error conditions, ED prints the message BREAK X AT C where X is one of the error indicators shown in Table 2-4.

If there is a disk error, CP/M displays the following message:

     BDOS ERR on d: BAD SECTOR

You can choose to ignore the error by pressing RETURN at the console (in this case, the memory buffer data should be examined to see if they were incorrectly read), or you can reset the system with a CTRL-C and reclaim the backup file if it exists. The file can be reclaimed by first typing the contents of the BAK file to ensure that it contains the proper information. For example, type the following:

     TYPE x.BAK

where x is the file being edited. Then remove the primary file

     ERA x.y

and rename the BAK file

     REN x.y=x.BAK

The file can then be reedited, starting with the previous version.

ED also takes file attributes into account. If you attempt to edit a Read-Only file, the message

     ** FILE IS READ/ONLY **

appears at the console. The file can be loaded and examined, but cannot be altered. You must end the edit session and use STAT to change the file attribute to Riw. If the edited file has the system attribute set, the following message:

     'SYSTEM' FILE NOT ACCESSIBLE

is displayed and the edit session is aborted. Again, the STAT program can be used to change the system attribute, if desired.

2.3 Control Characters and Commands

Table 2-5 summarizes the control characters and commands available in ED.

Table 2-6 summarizes the commands used in ED.

     free/total

Because of common typographical errors, ED requires several potentially disastrous commands to be typed as single letters, rather than in composite commands. The following commands:

• E(end)
• H(head)
• O(original)
• Q(quit)

must be typed as single letter commands.

The commands I, J, M, N, R, and S should be typed as i, j, m, n, r, and s if both upper- and lower-case characters are used in the operation, otherwise all characters are converted to upper-case. When a command is entered in upper-case, ED automatically converts the associated string to upper-case, and vice versa.

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