bfs(1)
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bfs Command
big file scanner
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SYNTAX
bfs [ - ] name
DESCRIPTION
The bfs command is like ed(1), but it is read-only and processes
much larger files. Files can be up to 1024K bytes and 32K lines,
with up to 512 characters, including newline. Bfs is usually
more efficient than ed for scanning a file, since the file is not
copied to a buffer. It is most useful for identifying sections
of a large file where csplit(1) can divide it into more
manageable pieces for editing.
Normally, the size of the file being scanned is printed, as is
the size of any file written with the w command. The optional -
suppresses printing of sizes. Input is prompted with * if you
type P and a newline as in ed. Turn prompting off again by
inputting another P and newline. Note that messages are given in
response to errors if prompting is turned on.
All address expressions described under ed are supported. In
addition, regular expressions may be surrounded with two symbols
besides / and ?: > indicates downward search without wrap-
around, and < indicates upward search without wrap-around. For
mark names, only the letters a through z may be used, and all 26
marks are remembered.
The e, g, v, k, p, q, w, =, ! and null commands operate as
described under ed. Commands such as ---, +++-, +++=, -12, and
+4p are accepted. Note that 1,10p and 1,10 will both print the
first ten lines. The f command prints only the name of the file
being scanned; there is no remembered file name. The w command
is independent of output diversion, truncation, or crunching (see
the xo, xt and xc commands, below). The following additional
commands are available:
xf file
Further commands are taken from the named file. When
an end-of-file is reached, an interrupt signal is
received, or an error occurs, reading resumes with the
file containing the xf. The xf commands may be nested
to a depth of 10.
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bfs(1)
xn List the marks currently in use (marks are set by the k
command).
xo [file]
Further output from the p and null commands is diverted
to the named file, which, if necessary, is created mode
666. If file is missing, output is diverted to the
standard output. Note that each diversion truncates or
creates the file.
: label
This positions a label in a command file. The label is
terminated by newline, and blanks between the : and the
start of the label are ignored. This command also
inserts comments into a command file, since labels need
not be referenced.
( . , . )xb/regular expression/label
A jump (either upward or downward) is made to label if
the command succeeds. It fails if:
Either address is not between 1 and $.
The second address is less than the first, or
The regular expression does not match at least
one line in the specified range, including the
first and last lines.
On success, . is set to the line matched and a jump is
made to label. If the command fails, the jump is not
made and the next statement is executed. This command
is the only one that does not issue an error message on
bad addresses, so you can use it to test whether
addresses are bad before other commands are executed.
Note that the command
xb/^/ label
is an unconditional jump.
The xb command is allowed only if it is read from
someplace other than a terminal. If it is read from a
pipe, only a downward jump is possible.
xt number
Output from the p and null commands is truncated to at
most number characters. The initial number is 255.
xv[digit][spaces][value]
The variable name is the specified digit following the
xv. The commands xv5100 or xv5 100 both assign the
value 100 to the variable 5. The command Xv61,100p
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bfs(1)
assigns the value 1,100p to the variable 6. To
reference a variable, put a % in front of the variable
name. For example, using the above assignments for
variables 5 and 6:
1,%5p
1,%5
%6
will all print the first 100 lines.
g/%5/p
would globally search for the characters 100 and print
each line containing a match. To escape the special
meaning of %, a \ must precede it.
g/".*\%[cds]/p
could be used to match and list lines containing printf
of characters, decimal integers, or strings.
Another feature of the xv command is that the first
line of output from a DG/UX system command can be
stored into a variable. The only requirement is that
the first character of value be !. For example:
.w junk
xv5!cat junk
!rm junk
!echo "%5"
xv6!expr %6 + 1
would put the current line into variable 5, print it,
and increment the variable 6 by one. To escape the
special meaning of ! as the first character of value,
precede it with a \.
xv7\!date
stores the value !date into variable 7.
xbz label
xbn label
These two commands will test the last saved return code
from the execution of a DG/UX system command (!command)
or nonzero value, respectively, to the specified label.
The two examples below search for the next five lines
containing the string size.
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xv55
: l
/size/
xv5!expr %5 - 1
!if 0%5 != 0 exit 2
xbn l
xv45
: l
/size/
xv4!expr %4 - 1
!if 0%4 = 0 exit 2
xbz l
xc [switch]
If switch is 1, output from the p and null commands is
crunched; if switch is 0 it is not. Without an
argument, xc reverses switch. Initially switch is set
for no crunching. Crunched output has strings of tabs
and blanks reduced to one blank and blank lines
suppressed.
SEE ALSO
csplit(1), ed(1).
regcmp(3X) in the Programmer's Reference for the DG/UX System
DIAGNOSTICS
? for errors in commands, if prompting is turned off. Self-
explanatory error messages when prompting is on.
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