BFS(1) RISC/os Reference Manual BFS(1)
NAME
bfs - big file scanner
SYNOPSIS
bfs [ - ] file
DESCRIPTION
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 characters, including
new-line, per line (255 for 16-bit machines). bfs is usu-
ally more efficient than ed for scanning a file, since the
file is not copied to a buffer. It is most useful for iden-
tifying sections of a large file where the csplit command
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.
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 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 ---, +++-1, +++=, -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 file name.
The w command is independent of output diversion, trunca-
tion, 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 sig-
nal 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).
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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 dictates oth-
erwise; see umask(1). 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:
Either address is not between 1 and $.
The second address is less than the first.
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 exe-
cuted. 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
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BFS(1) RISC/os Reference Manual BFS(1)
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
all print 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.
g/".*\%[cds]/p
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 require-
ment is that the first character of value be an !.
For example:
.w junk
xv5!cat junk
!rm junk
!echo "%5"
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 \.
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 system command (!com-
mand) or nonzero value, respectively, to the
specified label. The two examples below both
search for the next five lines containing the
string size.
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BFS(1) RISC/os Reference Manual BFS(1)
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 com-
mands is crunched; if switch is 0 it is not.
Without an argument, xc reverses switch. Ini-
tially switch is set for no crunching. Crunched
output has strings of tabs and blanks reduced to
one blank and blank lines suppressed.
INTERNATIONAL FUNCTIONALITY
bfs can process characters from supplementary code sets in
the text as well as ASCII characters.
bfs can also recognize labels containing characters from
supplementary code sets for :, xb, xbn and xbz commands.
Regular expression searches are performed on characters, not
on individual bytes. Refer to ed(1).
The value designated by number with the xt command must be
the number of displayed columns, not the number of charac-
ters.
Marks set by the k command must be ASCII characters in the
range of a to z, and all 26 marks are remembered.
WARNING
Size Indication
The size of the file displayed at first and after read/write
by the e or w commands is in bytes, not characters.
SEE ALSO
csplit(1), ed(1), umask(1), regexp(5).
DIAGNOSTICS
? for errors in commands, if prompting is turned off.
Self-explanatory error messages when prompting is on.
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