pattern-directed scanning and processing language

awk [ -F fs ] [ -v var=value ] [ prog | -f progFile] [ - | inputFile [ VAR=VALUE]]

Scans each inputFile for lines that match any of a set of (optional) patterns in prog or -f progFile.

With each pattern there may be an action to be performed when a line matches .

- process input from stdin instead of inputFile
Constructs of the form VAR=VALUE are treated as an assignment and are executed at the time the inputFile is opened.
-v var=value are performed before prog is started ( any number of -vs may be used.)
-F fs a regular expression used as the input Field Separator .
An input line is normally made up of fields separated by fs
$1, $2, …, are field are references
$0 refers to the entire line. "123 aaa 999" has only 1 field ?? if FS is null, the input line is split into one character per field.

A pattern-action statement has the form

[pattern] [{ action }]

action statements are separated by newlines or semi-colons.
   if( expression ) statement [ else statement ]
   while( expression ) statement
   for( expression ; expression ; expression ) statement
   for( var in array ) statement
   do statement while( expression )
   { [ 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 implies $0, that is the entire input line.
String constants are quoted " ", with the usual C escapes recognized within.
Expressions take on string or numeric values as appropriate, and are built with operators + - * / % ^ (exponentiation), and concatenation (indicated by white space).
operators: ! ++ -- += -= *= /= %= ^= > > < < == != ?: .
Variables may be scalars, array elements (denoted x[i]) or fields, are initialized to the null.
Array subscripts may be strings.
Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.


print arguments output to standard output separated by Output Field Separator (default tab),
and terminated by the Output Record Separator (default \n(newLine)).
file and cmd may be literal names or parenthesized expressions; identical string values in different statements denote the same open file.
printf formats its expression list (Add a new line with \n)
The character % is followed by zero or more of the flags:

          example: printf "%6d %s", NR, $0

close(expr) closes the file or pipe expr.
fflush(expr) flushes any buffered output for the file or pipe expr.
exp, log, sqrt, sin, cos, and atan2 .
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(string,m,n) the nth-character substring of string that begins at position m counted from 1.
index(string,substr) the position in string where substr occurs, or 0 if it does not.
match(string,regex) the position in string where the regular expression regex occurs, or 0 if it does not.
                RSTART and RLENGTH are set to the position and length of the matched string.
split(string, array[,fs]) splits string into array elements array[1], array[2], … array[n], and returns ni. The separation is done with the regular expression fs or with the field separator FS if fs is not given or null splits the string into 1 array element per character.

sub(regex,repl[,string]) substitutes repl for the first occurrence of the regular expression regex in string. $0 is the default for string .
gsub global replacement version of sub
 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.

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.
cmd | getline pipes the output of cmd into getline; each call of getline returns the next line of output from cmd.
getline returns 1 for a successful input, 0 for end of file, and -1 for an error.


Arbitrary boolean combinations (with ! || && of regular expressions and relational expressions as in egrep.
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 :

    expression matchop regular-expression
   expression relop expression
   expression in array-name
   (expr,expr,...) in array-name

matchop is either ~ (matches) or !~ (does not match).
relop is any < <= == >= > ! and

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).


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, local variables may be created by providing excess parameters in the function definition.


         If a line is longer than 80 characters wide; output the record Number, the begining and the end of line
  awk "{ if( length > 80 ) print NR,substr(\$0,1,16), \" -- \" substr(\$0,70,100 ); else print NR,\$0 }" /var/log/system.log
Given on the command line, the \s are needed to escape the $ and " from the shell intrepertation.
638 May  6 13:59:12   -- CaptivePublishState:1211 en1 - PreProbe
639 May  6 13:59:12 smackerPro configd[16]: network configuration changed.
640 May  6 13:59:12   -- fad0a750>: Stream error occurred for : The operation couldn’t be comple
641 May  6 13:59:12   -- fad0a750>: Stream error occurred for : The operation couldn’t be comple 

Print first two fields in opposite order.
{ print $2, $1 }

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

BEGIN { FS = ",[ \t]*|[ \t]+" }
{ print $2, $1 }

Add up first column, print sum and average.

{ s += $1 }
END { print "sum is", s, " average is", s/NR }

Print all lines between start/stop pairs.

/start/, /stop/ BEGIN { # Simulate echo(1)
for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
printf "\n"
exit }

Environment Varilables

> LC_ALL=en_US.UTF-8
Causes printf to output numbers values greater than 999 with commas when using ' in the format string.
Note: unset LC_ALL will not add commas!
 >ls -log sheet001.htm
-rw-r--r-- 1 6331 Feb  5 12:55 sheet001.htm

>export LC_ALL=en_US.UTF-8 
>ls -log sheet001.htm|\
>awk "{ printf \" %'d \\n\", \$3 }"   2>&1

SEE gawk,lex(1), sed(1)
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.