bfs - big file scanner
bfs [ - ] file
The bfs command is similar to ed 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 bytes, including new-line, per line (255 for 16-bit
machines). 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 the csplit command can be used
to divide it into more manageable pieces for editing.
bfs processes supplementary code set characters in file, and recognizes
supplementary code set characters in the labels given to the :, xb, xbn,
and xbz commands (see below) according to the locale specified in the
LC_CTYPE environment variable (see LANG on environ(5)). In regular
expressions, pattern searches are performed on characters, not bytes, as
described on ed(1).
Normally, the size in bytes 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. Prompting can be turned off again
by inputting another P and carriage return. 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. There is a slight difference in mark names:
only the ASCII characters a through z may be used, and all 26 marks are
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 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. The xf commands may be nested to a depth of 10.
xn List the marks currently in use (marks are set by the k
xo [file] Further output from the p and null commands is diverted to
the named file, which, if necessary, is created with mode
666 (readable and writable by everyone), unless your umask
setting dictates otherwise; see umask(1). If file is
missing, output is diverted to the standard output. Note
that each diversion causes truncation or creation of the
: label This positions a label in a command file. The label is
terminated by new-line, and blanks between the : and the
label are ignored. This command may also be used to
insert comments into a command file, since labels need not
be referenced. label may contain supplementary code set
( . , . )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
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
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. label may contain
supplementary code set characters.
xt number Output from the p and null commands is truncated to at
most number displayed columns. The initial number is 255.
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:
all print the first 100 lines.
globally searches for the characters 100 and prints each
line containing a match. To escape the special meaning of
%, a \ must precede it.
could be used to match and list lines containing a 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:
xv6!expr %6 + 1
puts the current line into 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 \.
stores the value !date into variable 7.
xbn label These two commands test the last saved return code from
the execution of a UNIX system command (!command) or
nonzero value, respectively, to the specified label.
label may contain supplementary code set characters. The
two examples below both search for the next five lines
containing the string size.
xv5!expr %5 - 1
!if 0%5 != 0 exit 2
xv4!expr %4 - 1
!if 0%4 = 0 exit 2
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.
csplit(1), ed(1), umask(1), regexp(5).
? for errors in commands, if prompting is turned off. Self-explanatory
error messages when prompting is on.
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