The bfs command is (almost) 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 (write) 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; that is, 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:
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.
List the marks currently in use (marks are set by the k command).
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.
This positions a label in a command file. The label is terminated by new-line, and blanks between the : (colon) 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.
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, . (dot) 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.
Output from the p and null commands is truncated to, at most, number characters. 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:
1,%5p 1,%5 %6
could be used to match and list %c, %d, or %s formats (for example, "printf"-like statements) 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
stores the value !date into variable 7.
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
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.
The following operand is supported:
Any file up to 1024K bytes and 32K lines, with up to 512 characters, including new-line, per line (255 for 16-bit machines). filename can be a section of a larger file which has been divided into more manageable sections for editing by the use of csplit(1).
The following exit values are returned:
Successful completion without any file or command errors.
An error occurred.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|
Message is ? for errors in commands, if prompting is turned off. Self-explanatory error messages are displayed when prompting is on.