For most of your applications, you do not need to underscore or
overstrike characters or character strings. If you are using a
typewriter terminal and are typing files that use backspaces and
underscores, you should use either the IMAGE OFF or IMAGE CANON subcommands so that the editor handles the backspaces properly. IMAGE CANON is the default value for SCRIPT files. CANON means that regardless of how the characters are keyed in
(characters, backspaces, underscores), the editor orders, or canonizes,
the characters in the file as: character-backspace-underscore,
character-backspace-underscore, and so on. If, for example, you want an
input line to look like: YOU could enter it as:
ABC, 3 backspaces, 3 underscores
- or -
3 underscores, 3 backspaces, ABC
A typewriter types out the line in the following order:
A backspace, underscore
B backspace, underscore
C backspace, underscore, which results in: If you need to modify a line that has backspaces, and you do not want
to rekey all of the characters, backspaces, and overstrike characters in
a CHANGE or REPLACE subcommand, you can use the ALTER subcommand to
alter all of the backspaces to some other character and use a global
CHANGE command. For example, the following sequences shows how to
delete all of the backspace characters on a line:
AAAAA alter 16 + 1 *
+A_+A_+A_+A_+A
change /_+// 1 *
AAAAA
This technique may also be useful on a display terminal. SETTING TRUNCATION LIMITS Every CMS file that you edit has a truncation column setting: this
column represents the last character position in a record into which you
can enter data. When you try to input a record that is longer than the
truncation column, the record is truncated, and the editor sends you a
message telling you that it has been truncated. You can change the truncation column setting with the TRUNC subcommand. For example, if you are creating a file with a record length
of 80 and wish to insert some records that do not extend beyond column 20, you could issue the subcommand:
trunc 20 78 IBM VM/370 CMS User's Guide

Then, when you enter data lines, any line that is longer than 20 characters is truncated and the editor sends you a message. If you are entering data in input mode, your virtual machine remains in input mode. When you use the CHANGE subcommand to modify records, the at
which truncation occurs is determined by the current zone setting. If
you change a character string in a line to a longer 'string, and the
resultant line extends beyond the current end zone, you receive the
message:
TRUNCATED.
If you need to create a line longer than the current end zone setting,
use the ZONE subcommand to increase the setting. The subcommand:
zone 1 *
extends the zone to the record length of the file. If the end zone
already equals the record length, you have to write the file onto disk
and reissue the EDIT subcommand specifying a longer record length.
For most filetypes, the truncation and end zone columns are the same
as the record length. For some filetypes, however, data is truncated
short of the record length. The default truncation and end zone columns
are: ASSEMBLE, MACRO UPDATE, UPDTxxxx AMSERV, COBOL, DIRECT, FORTRAN PLI, PLIOPT 72
All other filetypes are truncated at their record length. You can, when creating files for your own uses, set truncation
columns so that data does not extend beyond particular columns.
ENTERING A CONTINUATION CHARACTER IN COLUMN 72 When you are using the editor to enter source records for an assembler
language program and you need to enter a continuation character in
column 72, or whenever you want to enter data outside a particular
truncation setting, you can use the following technique. Note that this
technique will not work if CANON is specified on the IMAGE subcommand.
1. Change the truncation setting to 72, so that the editor does not
truncate the continuation character:
trunc 72
2. Use the TABSET subcommand to set the left margin at column 72: 72
3. Use the OVERLAY subcommand to overlay an asterisk in column 72:
overlay * Since the left margin is set at 72, the OVERLAY subcommand line
results in the character * being placed in column 72. Section 5. The CMS Editor' 79