AWK

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 patterns in prog or -f progFile.

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

- 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 field separator is a regular expression which breaks up an input line, $0 into fields $1, $2, …, .

awkprog.sh "123 aaa 999" has only 1 field

if FS is null each character is a 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 )
   break
   continue
   { [ statement] }
   expression # commonly var = 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
   print [ expression-list ] [ > expression ]
   printf format [ , expression-list ] [ > expression ]
          An empty expression-list implies $0, that is the entire input line.

Statements are terminated by semicolons, newlines or right braces.
String constants are " quoted ", with escapes \a, \t, \r, \n, \" , \e , \c and \xXX 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.

actions

print arguments are formatted and output to standard output ( or >file , >> appends to file)
separated by OFS(default tab) and terminated by the ORS(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:
# The value is converted to an alternate form.
x and X a non-zero result has the string 0x (or 0X for X conversions) prepended to it.
a, A, e, E, f, F, g, and G the result will always contain a decimal point, even if no digits follow it (normally, a decimal point appears in the results of those conversions only if a digit follows).
g and G trailing zeros are not removed from the result as they would otherwise be.
o (octal) the first character of the output string is made zero (by prefixing a 0 if it was not zero already).
For other conversions, the result is undefined.
- The converted value is left adjusted on the field boundary.
Default: right justification, except for n conversions, the converted value is padded on the right with blanks, rather than on the left with blanks or zeros.
0 The value is zero filled.
For d, i, o, u, x, X, a, A, e, E, f, F, g, and G the value is filled on the left with zeros.
If 0 and - are present, 0 is ignored.
If a precision is given with a numeric conversion (d, i, o, u, x, and X), 0 is ignored.
space A blank is left before a positive number (or empty string) produced by a signed conversion.
+ A sign, + or -, is placed before a number produced by a signed conversion.
Default: a sign is used only for negative numbers. A + overrides a space if both are used. The flag characters above are defined in the C standard.
' For decimal conversion (i, d, u, f, F, g, G) the output is to be grouped with thousands' grouping characters if the locale information provides any.
I For decimal integer conversion (i, d, u) the output uses the locale's alternative output digits.
For example, this will give Arabic-Indic digits in the Persian ('fa_IR') locale.

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

sprintf(fmt, expr, … ) the string resulting from formatting
close(expr) closes the file or pipe expr. fflush(expr) flushes buffered output.
exp log
sqrt
sin cos 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) begins at position m (counted from 1) nth-character substring of string
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 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.

system(cmd) executes cmd and returns its exit status

tolower(str) returns a copy of str with all upper-case characters translated to lower-case .
toupper(str) returns a copy of str with all lower-case characters translated to upper-case .

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

Patterns

The special patterns BEGIN and END may be used to capture control before the first input line is read and after the last and do not combine with other patterns.

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.

Keywords:

FILENAME the name of the current input file
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 (i.e. 1,2,3,4 …)
FNR ordinal number of the current record in the current 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 subscript separater (default ,)

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.

Examples

         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
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 }
#! /usr/bin/awk -f
# select lines where col 5 > 155 and seperate columns with + except field 5 use > <
BEGIN { FS=","}   # set Field Seperator BEFORE starting the program lest the first line use default FS (i.e. white space)

{
if( $5 >155) print NF, $1,"+",$2,"+",$3, "+",$4, ">",$5, "<",$6, "+",$7,"+",$8,"+",$9 
}

#! /usr/bin/awk -f
# output first column left justified and others right justified as in a load map.
{ printf "%-38s %8s %10s %s  %s", $1,$2, $3,$4, "\n" } 
echo system up for `uptime --pretty | awk '{ print $2*24+ $4 }'` minutes

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
 6,331 

SEE gawk,lex(1), sed(1)
To cast a string to a number add 0 to it;
To cast a number to a string concatenate "" to it.