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TAKE stage v1.1 |
Pipelines v2.1 |
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Syntax |
┌─FIRST─┐ ┌─1───────┐>>──TAKE──┬─┼───────┼──┼─────────┼──┬───────┬─┬──────────────────────────────────────><
│ └─LAST──┘ └─numrecs─┘ ├─BYTES─┤ │ │ └─CHARS─┘ │ └─┬─ALL─┬───────────────────────────┘ └─*───┘
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Purpose |
Use the TAKE stage to select one or more records from the beginning or end of its primary input stream. TAKE copies the selected records to its primary output stream. If its secondary output stream is connected, TAKE copies all other records to its secondary output stream, otherwise it discards the unselected records.
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Operands |
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● |
FIRST select records from the beginning of the input stream.
This is the default. |
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● |
LAST select records from the end of the input stream. |
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● |
ALL * specifies that all input records are selected and written to the primary output
stream. |
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● |
is an unsigned integer which specifies the number of records to be selected from the
input stream. The default is 1. If you specify 0 for numrecs, TAKE copies all of its input records to its secondary
output stream, if it is connected, otherwise TAKE discards the records and
the stage ends. |
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● |
BYTES Specifies that
the number of bytes is counted, rather than records. In general, the
specified number of bytes will be taken in the middle of a record, which is
then split after the last byte. When FIRST is specified the first part of the
split record is selected and the remainder is discarded. When LAST is
specified, the first part of the split record is discarded and the second
part is selected. |
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Streams
used |
The following streams are used by the TAKE stage:
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Usage
notes |
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1. |
TAKE
FIRST does not delay the records. TAKE
LAST delays the specified number of records. |
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2. |
TAKE
LAST stores the specified number of records in a buffer. For each subsequent
input record (if any), TAKE LAST writes the record residing longest in the
buffer to the secondary output stream, if it is connected. Otherwise, it
discards the record. The input record is then stored in the buffer, queued on
a first-in, first-out basis. When end-of-file is reached on the primary input
stream, TAKE LAST writes the specified number of records from the buffer to
the primary output stream, if it is connected, otherwise it discards the
records. |
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3. |
If the TAKE stage discovers that
all of its output streams are not connected, the TAKE stage ends. |
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4. |
TAKE FIRST disconnects its primary
output stream before it writes the unselected records to its secondary output
stream. TAKE LAST disconnects its secondary output stream before writing the
records to its primary output stream. |
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5. |
TAKE
verifies that its secondary input stream is not connected and then begins
execution. |
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Examples |
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1. |
The following pipeline reads the file in.txt and displays on the console only record number 10. **** Top of file ****1 Address Rxpipe 23 'pipe < in.txt', 4 '| drop first 9', 5 '| take 1', 6 '| console' 78 Exit 0 **** End of file ****
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2. |
To
display on the console the last 5 lines of a file; you might use the
following pipeline: 'pipe < myfile.txt | take last 5 | console'This approach, although using only a small
amount memory (enough to handle a working queue of up to 5 records), requires
the entire input file to be read, record by record, until the FILEIN stage
reaches the end-of-file on its input. For small files this may not be an
issue, however; for large files, this might require a significant amount of
I/O and time needed to traverse the entire input file. A better approach
might be to start reading the file in reverse record order, starting at the
end-of-file. The following example: Reading a file
backwards does exactly that. |
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Related |
DROP, FROMLABEL, HOLE, TOLABEL
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History |
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Version |
Date |
Action |
Description |
Pipelines |
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1.1 |
??.??.2025 |
changed |
Application-wide rewrite. |
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1.0 |
06.09.2007 |
created |
First version. |
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