Reads a single record from a specified input file and assigns the
record's contents to a specified symbol name.
Format
READ logical-name[:] symbol-name
1 – Parameters
logical-name[:]
Specifies the logical name of the input file from which a record
is to be read. Use the logical name assigned by the OPEN command
when the file was opened. (The OPEN command assigns a logical
name to a file and places the name in the process logical name
table.)
In addition, you can specify the process-permanent files
identified by the logical names SYS$INPUT, SYS$OUTPUT, SYS$ERROR,
and SYS$COMMAND.
symbol-name
Specifies the name of a symbol to be equated to the contents of
the record. The name must be 1 to 255 alphanumeric characters and
must start with an alphabetic letter, an underscore (_), or a
dollar sign ($).
When you specify a symbol name for the READ command, the command
interpreter places the symbol name in the local symbol table
for the current command level. If the symbol has already been
defined, the READ command redefines it to the new value being
read.
2 – Qualifiers
2.1 /DELETE
Deletes a record from an indexed file after it has been read. An
indexed file must be opened with the /READ and /WRITE qualifiers
in order to use the READ/DELETE command.
2.2 /END_OF_FILE
/END_OF_FILE=label
Transfers control to the location specified by the label keyword
(in the current command procedure) when the end of the file is
reached. When the last record in the file is read, the OpenVMS
Record Management Services (RMS) returns an error condition
indicating the end-of-file (EOF). If the /END_OF_FILE qualifier
is specified, the command interpreter transfers control to the
command line at the specified label.
If the /END_OF_FILE qualifier is not specified, control is given
to the error label specified with the /ERROR qualifier when the
end of the file is reached. If neither the /ERROR nor the /END_
OF_FILE qualifier is specified, then the current ON condition
action is taken.
2.3 /ERROR
/ERROR=label
Transfers control to the location specified by the label keyword
(in the current command procedure) when a read error occurs.
If no error routine is specified and an error occurs during the
reading of the file, the current ON condition action is taken.
Overrides any ON condition action specified.
If an error occurs and the target label is successfully given
control, the reserved global symbol $STATUS retains the error
code.
2.4 /INDEX
/INDEX=n
Specifies the index (n) to be used to look up keys when reading
an indexed file.
If you do not specify the /INDEX qualifier, the most recent
/INDEX qualifier value is used. If a previous value was not
specified, the primary index is used (/INDEX=0).
2.5 /KEY
/KEY=string
Reads a record with the key that matches the specified character
string. Binary and integer keys are not allowed. This qualifier,
when used together with the /INDEX qualifier, allows you random
access to indexed files.
Key matches are made by comparing the characters in the /KEY
string to characters in the record key.
To read records at random in an indexed file, you must specify
the /KEY qualifier. Once a record is read randomly, all
subsequent reads without the /KEY qualifier access records in
the indexed file sequentially.
2.6 /MATCH
/MATCH=option
Specifies the key match algorithm to be used when searching for
matching keys. Specify one of the following options:
EQ Selects keys equal to the match value (default).
GE Selects keys greater than or equal to the match value.
GT Selects keys greater than the match value.
LE Selects keys less than or equal to the match value.
LT Selects keys less than the match value.
If you are reading indexed files and you do not use the /MATCH
qualifier, the default is /MATCH=EQ.
2.7 /NOLOCK
Specifies that the record to be read not be locked and enables a
record to be read that has been locked by other accessors.
By default, records are locked as they are read and unlocked on
the next I/O operation on the file.
2.8 /PROMPT
/PROMPT=string
Specifies an alternate prompt string to be displayed when reading
from the terminal. The default prompt string is DATA:.
2.9 /TIME_OUT
/TIME_OUT=n
/NOTIME_OUT (default)
Specifies the number of seconds after which the READ command is
terminated if no input is received. If you enter the /TIME_OUT
qualifier, you must specify a value from 0 to 255.
If you enter both the /ERROR=label and /TIME_OUT qualifiers, and
the time limit expires, the error branch is taken.
2.10 /WAIT
Sets RAB$V_WAT to make a process wait for a record in a file. Can
be used in combination with /TIME_OUT to restrict how long the
process should wait before timing out upon failure to find the
record.
3 – Examples
1.$ OPEN IN NAMES.DAT
$ LOOP:
$ READ/END_OF_FILE=ENDIT IN NAME
.
.
.
$ GOTO LOOP
$ ENDIT:
$ CLOSE IN
The OPEN command opens the file NAMES.DAT for input and assigns
it the logical name of IN. The READ command reads records from
the file IN and places the contents into the symbol NAME. The
READ command specifies the label ENDIT to receive control when
the last record in the file has been read. The procedure loops
until all records in the file have been processed.
2.$ READ/ERROR=READERR/END_OF_FILE=OKAY MSGFILE CODE
.
.
.
$ READERR:
$ CLOSE MSGFILE
.
.
.
$ OKAY:
$ CLOSE MSGFILE
$ EXIT
The READ command reads records from the file MSGFILE and
places the contents into the symbol CODE. The READ command
also uses the /ERROR and /END_OF_FILE qualifiers to specify
labels to receive control at the end-of-file (EOF) and on
error conditions. At the EOF, control is transferred to the
label OKAY. On other read errors, control is transferred to the
READERR label.
3.$ READ SYS$COMMAND DATA_LINE
$ WRITE OUTPUT_FILE DATA_LINE
.
.
.
The READ command requests data from the current SYS$COMMAND
device. If the command procedure containing these lines is
executed interactively, the command issues a prompt to the
terminal, accepts a line of data, and equates the data entered
to the symbol name DATA_LINE.
Then the WRITE command writes the value of the symbol DATA_LINE
to the file identified by the logical name OUTPUT_FILE.
4.$ OPEN/READ INPUT_FILE TRNTO::INVENTORY.DAT
$ OPEN/APPEND OUTPUT_FILE RECEIVE.DAT
$ READ INPUT_FILE DATA_LINE
$ WRITE OUTPUT_FILE DATA_LINE
The OPEN/READ command opens the file INVENTORY.DAT at the
remote node TRNTO for reading and assigns it the logical name
INPUT_FILE. The OPEN/APPEND command opens the file RECEIVE.DAT
in the current default directory. The READ command requests
data from the file INVENTORY.DAT at the remote node TRNTO. The
WRITE command writes the value of the symbol DATA_LINE to the
end of the local file RECEIVE.DAT.