Awk tutorial: awk man

awk man

ylspiritdeMacBook-Pro:awk ylspirit$ man 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 executed; 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 statements 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 + - * / % ^ (exponentia-
       tion),  and concatenation (indicated by white space).  The operators ! ++ -- += -= *= /= %= ^= > >= < <= == != ?: are also available in expressions.  Vari-
       ables may be scalars, array elements (denoted x[i]) or fields.  Variables are initialized to the null string.  Array subscripts may be any string, not nec-
       essarily numeric; this allows for a form of associative memory.  Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, sep-
       arated 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 terminated by the output record separator.  file and cmd may be literal names or parenthesized expressions; identi-
       cal string values in different statements denote the same open file.  The printf statement 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 functions:

       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 variable) 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 variables 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.

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