gawk.hlp

早期freebsd实现

 command or a variable with a string value representing such a
 command.

 To output into a file other that the primary output, use
     print x,... > "file"    (or >> "file")
 or  printf(f,x,...) > "file"    (or >> "file")
 similar to the 'getline' example above.  '>>' causes output to be
 appended to an existing file if it exists, or create the file if
 it doesn't already exist.  '>' always creates a new file.  The
 alternate redirection method of '>$' (for RMS text file attributes)
 is *only* available on the command line, not with 'print' or
 'printf' in  the current release.

 To output an error message, use 'print' or 'printf' and redirect
 the output to file "/dev/stderr" (or equivalently to "SYS$ERROR:"
 on VMS).  'stderr' will normally be the user's terminal, even if
 ordinary output is being redirected into a file.

 To feed awk output into another command, use
     print x,... | "command"    (similarly for 'printf')
 similar to the second 'getline' example.  In this case, output
 from awk will be passed as input to the specified operating system
 command.  The command must be capable of reading input from 'stdin'
 ("SYS$INPUT:" on VMS) in order to receive data in this manner.

 The 'close' function operates on the "file" or "command" argument
 specified here (either a literal string or a variable or expression
 resulting in a string value).  It completely closes the file or
 pipe so that further references to the same file or command string
 would re-open that file or command at the beginning.  Closing a
 pipe or redirection also releases some file-oriented resources.

 Note:  the VMS implementation of GAWK uses temporary files to
 simulate pipes, so a command must finish before 'getline' can get
 any input from it, and 'close' must be called for an output pipe
 before any data can be passed to the specified command.
5 formats
 Formatting characters used by the 'printf' and 'sprintf' functions
 (each is introduced in the format string by preceding it with a
 percent sign (%))
   %   include a literal percent sign (%) in the result
   c   format the next argument as a single ASCII character
         (prints first character of string argument, or corresponding
         ASCII character if numeric argument, e.g. 65 is 'A')
   s   format the next argument as a string (numeric arguments are
         converted into strings on demand)
   d   decimal number (ie, integer value in base 10)
   i   integer (equivalent to decimal)
   o   octal number (integer in base 8)
   x   hexadecimal number (integer in base 16) [lowercase]
   X   hexadecimal number [digits 'A' thru 'E' in uppercase]
   f   floating point number (digits, decimal point, fraction digits)
   e   exponential (scientific notation) number (digit, decimal
         point, fraction digits, letter 'e', sign '+' or '-',
         exponent digits)
   g   'fractional' number in either 'e' or 'f' format, whichever
         produces shorter result

 Three optional modifiers can be placed between the initiating
 percent sign and the format character (doesn't apply to %%).
   -   left justify (only matters when width specifier is present)
   NN  width ['NN' represents 1 or more decimal digits]; actually
         minimum width to use, longer items will not be truncated; a
         leading 0 will cause right-justified numbers to be padded on
         the left with zeroes instead of spaces when they're aligned
   .MM precision [decimal point followed by 1 or more digits]; used
         as maximum width for strings (causing truncation if they're
         actually longer) or as number of fraction digits for 'f' or
         'e' numeric formats, or number of significant digits for 'g'
         numeric format
4 user_defined_functions
 User-defined functions may be created as needed to simplify awk
 programs or to collect commonly used code into one place.  The
 general syntax of a user-defined function is the 'function' keyword
 followed by unique function name, followed by a comma-separated
 parameter list enclosed in parentheses, followed by statement(s)
 enclosed within braces ({}).  A 'return' statement is customary
 but is not required.
       function FuncName(arg1,arg2) {
           # arbitrary statements
           return (arg1 + arg2) / 2
       }
 If a function does not use 'return' to specify an output value, the
 result received by the caller will be unpredictable.

 Functions may be placed in an awk program before, between, or after
 the pattern-action rules.  The abbreviation 'func' may be used in
 place of 'function', unless POSIX compatibility mode is in effect.
3 regular_expressions
 A regular expression is a shorthand way of specifying a 'wildcard'
 type of string comparison.  Regular expression matching is very
 fundamental to awk's operation.

 Meta symbols
   ^   matches beginning of line or beginning of string; note that
         embedded newlines ('\n') create multi-line strings, so
         beginning of line is not necessarily beginning of string
   $   matches end of line or end of string
   .   any single character (except newline)
   [ ] set of characters; [ABC] matches either 'A' or 'B' or 'C'; a
         dash (other than first or last of the set) denotes a range
         of characters: [A-Z] matches any upper case letter; if the
         first character of the set is '^', then the sense of match
         is reversed: [^0-9] matches any non-digit; several
         characters need to be quoted with backslash (\) if they
         occur in a set:  '\', ']', '-', and '^'
   |   alternation (similar to boolean 'or'); match either of two
         patterns [for example "^start|stop$" matches leading 'start'
         or trailing 'stop']
   ( ) grouping, alter normal precedence [for example, "^(start|stop)$"
         matches lines reading either 'start' or 'stop']
   *   repeated matching; when placed after a pattern, indicates that
         the pattern should match any number of times [for example,
         "[a-z][0-9]*" matches a lower case letter followed by zero or
         more digits]
   +   repeated matching; when placed after a pattern, indicates that
         the pattern should match one or more times ["[0-9]+" matches
         any non-empty sequence of digits]
   ?   optional matching; indicates that the pattern can match zero or
         one times ["[a-z][0-9]?" matches lower case letter alone or
         followed by a single digit]
   \   quote; prevent the character which follows from having special
         meaning

 A regular expression which matches a string or line will match against
 the first (left-most) substring which meets the pattern and include
 the longest sequence of characters which still meets that pattern.
3 comments
 Comments in awk programs are introduced with '#'.  Anything after
 '#' on a line is ignored by GAWK.  It's a good idea to include an
 explanation of what an awk program is doing and also who wrote it
 and when.
3 further_information
 For complete documentation on GAWK, see "The_GAWK_Manual" from FSF.
 Source text for it is present in the file GAWK.TEXINFO.  A postscript
 version is available via anonymous FTP from host prep.ai.mit.edu in
 directory pub/gnu/.

 For additional documentation on awk--above and beyond that provided in
 The_GAWK_Manual--see "The_AWK_Programming_Language" by Aho, Weinberger,
 and Kernighan (2nd edition, 1988), published by Addison-Wesley.  It is
 both a reference on the awk language and a tutorial on awk's use, with
 many sample programs.
3 authors
 The awk programming language was originally created by Alfred V. Aho,
 Peter J. Weinberger, and Brian W. Kernighan in 1977.  The language
 was revised and enhanced in a new version which was released in 1985.

 GAWK, the GNU implementation of awk, was written in 1986 by Paul Rubin
 and Jay Fenlason, with advice from Richard Stallman, and with
 contributions from John Woods.  In 1988 and 1989, David Trueman and
 Arnold Robbins revised GAWK for compatibility with the newer awk.

 GAWK version 2.11.1 was ported to VMS by Pat Rankin in November, 1989,
 with further revisions in the Spring of 1990.  The VMS port was
 incorporated into the official GNU distribution of version 2.13 in
 Spring 1991.  (Version 2.12 was never publically released.)
2 release_notes
 GAWK 2.14 tested under VMS V5.5, July, 1992; compatible with VMS
 versions V4.6 and later.  Current source code compatible with DEC's
 VAXC v3.x and v2.4 or v2.3; also compiles successfully with GNUC
 (GNU's gcc).  VMS POSIX uses c89 and requires VAXC V3.x.
3 AWK_LIBRARY
 GAWK uses a built in search path when looking for a program file
 specified by the -f option (or the /input qualifier) when that file
 name does not include a device and/or directory.  GAWK will first
 look in the current default directory, then if the file wasn't found
 it will look in the directory specified by the translation of logical
 name "AWK_LIBRARY".

 Not applicable under VMS POSIX.
3 known_problems
 There are several known problems with GAWK running on VMS.  Some can
 be ignored, others require work-arounds.  Note: GAWK in the VMS POSIX
 environment does not have these problems.
4 command_line_parsing
 The command
       gawk "program text"
 will pass the first phase of DCL parsing (the single required
 parameter is present), then it will give an error that a required
 element (either /input=awk_file or /commands="program text") is
 missing.  If what was intended (as is most likely) is to pass the
 program text to the UN*X-style command interface, the following
 variation is required
       gawk -- "program text"
 The presence of "--", which is normally optional, will inhibit the
 attempt to use DCL parsing (as will any '-' option or redirection).
4 file_formats
 If a file having the RMS attribute "Fortran carriage control" is
 read as input, it will generate an empty first record if the first
 actual record begins with a space (leading space becomes a newline).
 Also, the last record of the file will give a "record not terminated"
 warning.  Both of these minor problems are due to the way that the
 C Run-Time Library (VAXCRTL) converts record attributes.

 Another poor feature without a work-around is that there's no way to
 specify "append if possible, create with RMS text attributes if not"
 with the current command line I/O redirection.  '>>$' isn't supported.
4 RS_peculiarities
 Changing the record separator to something other than newline ('\n')
 will produce anomalous results for ordinary files.  For example,
 using RS = "\f" and FS = "\n" with the following input
       |rec 1, line 1
       |rec 1, line 2
       |^L    (form feed)
       |rec 2, line 1
       |rec 2, line 2
       |^L    (form feed)
       |rec 3, line 1
       |rec 3, line 2
       |(end of file)
 will produce two fields for record 1, but three fields each for
 records 2 and 3.  This is because the form-feed record delimiter is
 on its own line, so awk sees a newline after it.  Since newline is
 now a field separator, records 2 and 3 will have null first fields.
 The following awk code will work-around this problem by inserting
 a null first field in the first record, so that all records can be
 handled the same by subsequent processing.
       # fix up for first record (RS != "\n")
       FNR == 1  { if ( $0 == "" )     #leading separator
                     next              #skip its null record
                   else                #otherwise,
                     $0 = FS $0        #realign fields
                 }
 There is a second problem with this same example.  It will always
 trigger a "record not terminated" warning when it reaches the end of
 file.  In the sample shown, there is no final separator; however, if
 a trailing form-feed were present, it would produce a spurious final
 record with two null fields.  This occurs because the I/O system
 sees an implicit newline at the end of the last record, so awk sees
 a pair of null fields separated by that newline.  The following code
 fragment will fix that provided there are no null records (in this
 case, that would be two consecutive lines containing just form-feeds).
       # fix up for last record (RS != "\n")
       $0 == FS  { next }      #drop spurious final record
 Note that the "record not terminated" warning will persist.
4 cmd_inconsistency
 The DCL qualifier /OUTPUT is internally equivalent to '>$' output
 redirection, but the qualifier /INPUT corresponds to the -f option
 rather than to '<' input redirection.
4 exit
 The exit statement can optionally pass a final status value to the
 operating system.  GAWK expects a UN*X-style value instead of a
 VMS status value, so 0 indicates success and non-zero indicates
 failure.  The final exit status will be 1 (VMS success) if 0 is
 used, or even (VMS non-success) if non-zero is used.
3 changes
 Changes between version 2.14 and 2.13.2:

   General
     'next file' construct added
     'continue' outside of any loop is treated as 'next'
     Assorted bug fixes and efficiency improvements
     _The_GAWK_Manual_ updated
     Test suite expanded

   VMS-specific
     VMS POSIX support added
     Disk I/O throughput enhanced
     Pipe emulation improved and incorrect interaction with user-mode
         redefinition of SYS$OUTPUT eliminated
3 prior_changes
 Changes between version 2.13 and 2.11.1:  (2.12 was not released)

   General
     CONVFMT and FIELDWIDTHS builtin control variables added
     systime() and strftime() date/time functions added
     'lint' and 'posix' run-time options added
     '-W' command line option syntax supercedes '-c', '-C', and '-V'
     '-a' and '-e' regular expression options made obsolete
     Various bug fixes and efficiency improvements
     More platforms supported ('officially' including VMS)

   VMS-specific
     %g printf format fixed
     Handling of '\' on command line modified; no longer necessary to
         double it up
     Problem redirecting stderr (>&efile) at same time as stdin (<ifile)
         or stdout (>ofile) has been fixed
     ``2>&1'' and ``1>&2'' redirection constructs added
     Interaction between command line I/O redirection and gawk pipes
         fixed; also, name used for pseudo-pipe temporary file expanded
3 license
 GAWK is covered by the "GNU General Public License", the gist of which
 is that if you supply this software to a third party, you are expressly
 forbidden to prevent them from supplying it to a fourth party, and if
 you supply binaries you must make the source code available to them
 at no additional cost.  Any revisions or modified versions are also
 covered by the same license.  There is no warranty, express or implied,
 for this software.  It is provided "as is."

 [Disclaimer:  This is just an informal summary with no legal basis;
 refer to the actual GNU General Public License for specific details.]
!2 examples
!