BFS(1) SysV BFS(1)
NAME
bfs - big file scanner
SYNOPSIS
bfs [ - ] name
DESCRIPTION
bfs is like ed(1) except that 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 new-line, per line (255 for 16-bit machines). bfs
is usually more efficient than ed(1) 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 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 - suppresses
printing of sizes. Input is prompted with * if P and a carriage return
are typed, as in ed(1). Prompting can be turned off again by inputting
another P and carriage return. Note that messages are given in response
to errors if prompting is turned on.
All address expressions described under ed(1) 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. There is 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(1). 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 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.
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 (readable
and writable by everyone), unless your umask setting (see
umask(1)) dictates otherwise. 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 new-line, 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 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. This command is the only one that does not 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 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 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 UNIX system command can be stored into a
variable. The only requirement is that the first character of
value be an !. 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 UNIX system command (!command) or nonzero
value, respectively, to the specified label. The two examples
below both 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.
DIAGNOSTICS
? for errors in commands, if prompting is turned off. Self-explanatory
error messages when prompting is on.
SEE ALSO
csplit(1), ed(1), umask(1).