BFS(C) UNIX System V
Name
bfs - scans big files
Syntax
bfs [ - ] name
Description
bfs is like ed(C) except that it is read-only and processes
much larger files. Files can be up to 1024K bytes and 32K
lines, with up to 255 characters per line. 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(C) can be
used to 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 dash (-) suppresses printing of sizes. Input is
prompted for with an asterisk (*) when ``P'' and RETURN are
typed. The ``P'' acts as a toggle, so prompting can be
turned off again by entering another ``P'' and a RETURN.
Note that messages are given in response to errors only if
prompting is turned on.
All address expressions described under ed are supported.
In addition, regular expressions may be surrounded with two
symbols other than the standard slash (/) and (?): A
greater-than sign (>) indicates downward search without
wraparound, and a less-than sign (<) indicates upward search
without wraparound. Note that parentheses and curly braces
are special and need to be escaped with a backslash (\).
Since bfs uses a different regular expression-matching
routine from ed, the regular expressions accepted are
slightly wider in scope (see regex(S)). Differences between
ed and bfs are listed below:
+ A regular expression followed by + means one or
more times. For example, [0-9]+ is equivalent to
[0-9][0-9]*.
\{m\} \{m,\} \{m,u\}
Integer values enclosed in \{\} indicate the
number of times the preceding regular expression
is to be applied. m is the minimum number and u
is a number, less than 256, which is the maximum.
If only m is present (e.g., \{m\}), it indicates
the exact number of times the regular expression
is to be applied. \{m,\} is analogous to
\{m,infinity\}. The plus (+) and star (*)
operations are equivalent to \{1,\} and \{0,\}
respectively.
( ... )$n The value of the enclosed regular expression is to
be returned. The value will be stored in the
(n+1)th argument following the subject argument.
At most ten enclosed regular expressions are
allowed. regex makes its assignments
unconditionally.
( ... ) Parentheses are used for grouping. An operator,
e.g. *, +, \{\}, can work on a single character
or a regular expression enclosed in parenthesis.
For example, \(a*\(cb+\)*\)$0.
There is also a slight difference in 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 except that e doesn't remember filenames
and g and v when given no arguments return the line after
the line you were on. 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 only prints
the name of the file being scanned; there is no remembered
filename. 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. xf commands may be nested to a
depth of 10.
xo [file]
Further output from the p and null commands is diverted
to the named file. If file is missing, output is
diverted to the standard output. Note that each
diversion causes truncation or creation of the file.
: label
This positions a label in a command file. The label is
terminated by a newline, and blanks between the : and
the start of the label are ignored. This command may
also be used to insert 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 under any of the
following conditions:
1. Either address is not between 1 and $.
2. The second address is less than the first.
3. The regular expression doesn't match at least one
line
in the specified range, including the first and
last lines.
On success, dot (.) is set to the line matched and a
jump is made to label. This command is the only one
that doesn't issue an error message on bad addresses,
so it may be used 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 somewhere
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 a
maximum of number characters. The initial number is 255.
xv[digit][spaces][value]
The variable name is the specified digit following the xv.
xv5100 or xv5 100 both assign the value 100 to the variable
5. xv61,100p 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
prints the first 100 lines.
g/%5/p
globally searches for the characters 100 and prints each
line containing a match. To escape the special meaning of
%, a \ must precede it. For example,
g/".*\%[cds]/p
could be used to match and list lines containing printf
characters, decimal integers, or strings.
Another feature of the xv command is that the first line of
output from a UNIX command can be stored into a variable.
The only requirement is that the first character of value be
a !. For example,
xv5!cat junk
!rm junk
!echo "%5"
xv6!expr %6 + 1
puts the current line in variable 5, prints it, and
increments the variable 6 by one. To escape the special
meaning of ! as the first character of value, precede it
with a \. For example,
xv7\!date
stores the value !date into variable 7.
xbz label
xbn label
These two commands test the last saved return code from the
execution of a UNIX command (!command) or nonzero value,
respectively, and jump to the specified label. The two
examples below search for the next five lines containing the
string size:
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(C), ed(C), umask(C)
Diagnostics
? for errors in commands if prompting is turned off. Self-
explanatory error messages when prompting is on.
(printed 2/15/90) BFS(C)