awk 用法

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AWK

awk

NAME

       awk - pattern-directed scanning and processing language

SYNOPSIS

       awk [ -F fs ] [ -v var=value ] [ 'prog' | -f progfile ] [ file ...  ]

DESCRIPTION

       Awk  scans  each input file for lines that match any of a set of patterns specified literally in prog

       or in one or more files specified as -f progfile.  With each  pattern  there  can  be  an  associated

       action  that  will  be  performed  when  a  line of a file matches the pattern.  Each line is matched

       against the pattern portion of every pattern-action statement; the associated action is performed for

       each  matched  pattern.  The file name - means the standard input.  Any file of the form var=value is

       treated as an assignment, not a filename, and is executed at the time it would have been opened if it

       were a filename.  The option -v followed by var=value is an assignment to be done before prog is exe-

       cuted; any number of -v options may be present.  The -F fs option defines the input  field  separator

       to be the regular expression fs.

       An  input  line  is normally made up of fields separated by white space, or by regular expression FS.

       The fields are denoted $1, $2, ..., while $0 refers to the entire line.  If FS  is  null,  the  input

       line is split into one field per character.

       A pattern-action statement has the form

              pattern { action }

       A  missing  { action } means print the line; a missing pattern always matches.  Pattern-action state-

       ments are separated by newlines or semicolons.

       An action is a sequence of statements.  A statement can be one of the following:

              if( expression ) statement [ else statement ]

              while( expression ) statement

              for( expression ; expression ; expression ) statement

              for( var in array ) statement

              do statement while( expression )

              break

              continue

              { [ statement ... ] }

              expression              # commonly var = expression

              print [ expression-list ] [ > expression ]

              printf format [ , expression-list ] [ > expression ]

              return [ expression ]

              next                    # skip remaining patterns on this input line

              nextfile                # skip rest of this file, open next, start at top

              delete array[ expression ]# delete an array element

              delete array            # delete all elements of array

              exit [ expression ]     # exit immediately; status is expression

       Statements are terminated by semicolons, newlines or right braces.  An empty  expression-list  stands

       for  $0.   String  constants are quoted " ", with the usual C escapes recognized within.  Expressions

       take on string or numeric values as appropriate, and are built using the operators + - * / % ^ (expo-

       nentiation), and concatenation (indicated by white space).  The operators ! ++ -- += -= *= /= %= ^= >

       >= < <= == != ?: are also available  in  expressions.   Variables  may  be  scalars,  array  elements

       (denoted x[i]) or fields.  Variables are initialized to the null string.  Array subscripts may be any

       string, not necessarily numeric; this allows for a form of associative memory.   Multiple  subscripts

       such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.

       The  print  statement prints its arguments on the standard output (or on a file if >file or >>file is

       present or on a pipe if |cmd is present), separated by the current output field separator, and termi-

       nated  by  the  output  record separator.  file and cmd may be literal names or parenthesized expres-

       sions; identical string values in different statements denote the same open file.  The printf  state-

       ment  formats  its  expression  list  according to the format (see printf(3)).  The built-in function

       close(expr) closes the file or pipe expr.  The built-in function fflush(expr)  flushes  any  buffered

       output for the file or pipe expr.

       The  mathematical  functions  exp, log, sqrt, sin, cos, and atan2 are built in.  Other built-in func-

       tions:

       length the length of its argument taken as a string, or of $0 if no argument.

       rand   random number on (0,1)

       srand  sets seed for rand and returns the previous seed.

       int    truncates to an integer value

       substr(s, m, n)

              the n-character substring of s that begins at position m counted from 1.

       index(s, t)

              the position in s where the string t occurs, or 0 if it does not.

       match(s, r)

              the position in s where the regular expression r occurs, or 0 if it does not.   The  variables

              RSTART and RLENGTH are set to the position and length of the matched string.

       split(s, a, fs)

              splits  the string s into array elements a[1], a[2], ..., a[n], and returns n.  The separation

              is done with the regular expression fs or with the field separator FS if fs is not given.   An

              empty string as field separator splits the string into one array element per character.

       sub(r, t, s)

              substitutes  t  for the first occurrence of the regular expression r in the string s.  If s is

              not given, $0 is used.

       gsub   same as sub except that all occurrences of the regular expression are replaced; sub  and  gsub

              return the number of replacements.

       sprintf(fmt, expr, ... )

              the string resulting from formatting expr ...  according to the printf(3) format fmt

       system(cmd)

              executes cmd and returns its exit status

       tolower(str)

              returns  a copy of str with all upper-case characters translated to their corresponding lower-

              case equivalents.

       toupper(str)

              returns a copy of str with all lower-case characters translated to their corresponding  upper-

              case equivalents.

       The  ``function'' getline sets $0 to the next input record from the current input file; getline <file

       sets $0 to the next record from file.  getline x sets variable x instead.   Finally,  cmd  |  getline

       pipes  the output of cmd into getline; each call of getline returns the next line of output from cmd.

       In all cases, getline returns 1 for a successful input, 0 for end of file, and -1 for an error.

       Patterns are arbitrary Boolean combinations (with ! || &&)  of  regular  expressions  and  relational

       expressions.   Regular expressions are as defined in re_format(7).  Isolated regular expressions in a

       pattern apply to the entire line.  Regular expressions may  also  occur  in  relational  expressions,

       using  the  operators ~ and !~.  /re/ is a constant regular expression; any string (constant or vari-

       able) may be used as a regular expression, except in the position of an isolated  regular  expression

       in a pattern.

       A pattern may consist of two patterns separated by a comma; in this case, the action is performed for

       all lines from an occurrence of the first pattern though an occurrence of the second.

       A relational expression is one of the following:

              expression matchop regular-expression

              expression relop expression

              expression in array-name

              (expr,expr,...) in array-name

       where a relop is any of the six relational operators in C, and a matchop is either ~ (matches) or  !~

       (does  not  match).  A conditional is an arithmetic expression, a relational expression, or a Boolean

       combination of these.

       The special patterns BEGIN and END may be used to capture control before the first input line is read

       and after the last.  BEGIN and END do not combine with other patterns.

       Variable names with special meanings:

       CONVFMT

              conversion format used when converting numbers (default %.6g)

       FS     regular expression used to separate fields; also settable by option -Ffs.

       NF     number of fields in the current record

       NR     ordinal number of the current record

       FNR    ordinal number of the current record in the current file

       FILENAME

              the name of the current input file

       RS     input record separator (default newline)

       OFS    output field separator (default blank)

       ORS    output record separator (default newline)

       OFMT   output format for numbers (default %.6g)

       SUBSEP separates multiple subscripts (default 034)

       ARGC   argument count, assignable

       ARGV   argument array, assignable; non-null members are taken as filenames

       ENVIRON

              array of environment variables; subscripts are names.

       Functions may be defined (at the position of a pattern-action statement) thus:

              function foo(a, b, c) { ...; return x }

       Parameters  are  passed  by  value  if scalar and by reference if array name; functions may be called

       recursively.  Parameters are local to the function; all other variables are global.  Thus local vari-

       ables may be created by providing excess parameters in the function definition.

EXAMPLES

       length($0) > 72

              Print lines longer than 72 characters.

       { print $2, $1 }

              Print first two fields in opposite order.

       BEGIN { FS = ",[ \t]*|[ \t]+" }

             { print $2, $1 }

              Same, with input fields separated by comma and/or blanks and tabs.

            { s += $1 }

       END  { print "sum is", s, " average is", s/NR }

              Add up first column, print sum and average.

       /start/, /stop/

              Print all lines between start/stop pairs.

       BEGIN     {    # Simulate echo(1)

            for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]

            printf "\n"

            exit }

SEE ALSO

       lex(1), sed(1)

       A.  V.  Aho,  B.  W. Kernighan, P. J. Weinberger, The AWK Programming Language, Addison-Wesley, 1988.

       ISBN 0-201-07981-X

BUGS

       There are no explicit conversions between numbers and strings.  To force an expression to be  treated

       as a number add 0 to it; to force it to be treated as a string concatenate "" to it.

       The scope rules for variables in functions are a botch; the syntax is worse.

                                                                                                      AWK