AWK(1) User Commands AWK(1)


NAME


awk - pattern scanning and processing language

SYNOPSIS


/usr/bin/awk [-f progfile] [-Fc] [' prog '] [parameters]
[filename]...


/usr/xpg4/bin/awk [-FcERE] [-v assignment]... 'program' -f progfile...
[argument]...


DESCRIPTION


The /usr/xpg4/bin/awk utility is described on the nawk(1) manual page.


The /usr/bin/awk utility scans each input filename for lines that match
any of a set of patterns specified in prog. The prog string must be
enclosed in single quotes ( a') to protect it from the shell. For each
pattern in prog there can be an associated action performed when a line
of a filename matches the pattern. The set of pattern-action statements
can appear literally as prog or in a file specified with the -f progfile
option. Input files are read in order; if there are no files, the
standard input is read. The file name '-' means the standard input.

OPTIONS


The following options are supported:

-f progfile
awk uses the set of patterns it reads from progfile.


-Fc
Uses the character c as the field separator (FS)
character. See the discussion of FS below.


USAGE


Input Lines


Each input line is matched against the pattern portion of every pattern-
action statement; the associated action is performed for each matched
pattern. Any filename 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. Variables assigned in this manner are not available
inside a BEGIN rule, and are assigned after previously specified files
have been read.


An input line is normally made up of fields separated by white spaces.
(This default can be changed by using the FS built-in variable or the -Fc
option.) The default is to ignore leading blanks and to separate fields
by blanks and/or tab characters. However, if FS is assigned a value that
does not include any of the white spaces, then leading blanks are not
ignored. The fields are denoted $1, $2, ...; $0 refers to the entire
line.

Pattern-action Statements
A pattern-action statement has the form:

pattern { action }


Either pattern or action can be omitted. If there is no action, the
matching line is printed. If there is no pattern, the action is performed
on every input line. Pattern-action statements are separated by newlines
or semicolons.


Patterns are arbitrary Boolean combinations ( !, ||, &&, and parentheses)
of relational expressions and regular expressions. A relational
expression is one of the following:

expression relop expression
expression matchop regular_expression


where a relop is any of the six relational operators in C, and a matchop
is either ~ (contains) or !~ (does not contain). An expression is an
arithmetic expression, a relational expression, the special expression

var in array


or a Boolean combination of these.


Regular expressions are as in egrep(1). In patterns they must be
surrounded by slashes. Isolated regular expressions in a pattern apply to
the entire line. Regular expressions can also occur in relational
expressions. A pattern can consist of two patterns separated by a comma;
in this case, the action is performed for all lines between the
occurrence of the first pattern to the occurrence of the second pattern.


The special patterns BEGIN and END can be used to capture control before
the first input line has been read and after the last input line has been
read respectively. These keywords do not combine with any other patterns.

Built-in Variables
Built-in variables include:

FILENAME
name of the current input file


FS
input field separator regular expression (default blank and
tab)


NF
number of fields in the current record


NR
ordinal number of the current record


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


OFS
output field separator (default blank)


ORS
output record separator (default new-line)


RS
input record separator (default new-line)


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

if ( expression ) statement [ else statement ]
while ( expression ) statement
do statement while ( expression )
for ( expression ; expression ; expression ) statement
for ( var in array ) statement
break
continue
{ [ statement ] ... }
expression # commonly variable = expression
print [ expression-list ] [ >expression ]
printf format [ ,expression-list ] [ >expression ]
next # skip remaining patterns on this input line
exit [expr] # skip the rest of the input; exit status is expr


Statements are terminated by semicolons, newlines, or right braces. An
empty expression-list stands for the whole input line. Expressions take
on string or numeric values as appropriate, and are built using the
operators +, -, *, /, %, ^ and concatenation (indicated by a blank). The
operators ++, --, +=, -=, *=, /=, %=, ^=, >, >=, <, <=, ==, !=, and ?:
are also available in expressions. Variables can be scalars, array
elements (denoted x[i]), or fields. Variables are initialized to the null
string or zero. Array subscripts can be any string, not necessarily
numeric; this allows for a form of associative memory. String constants
are quoted (""), with the usual C escapes recognized within.


The print statement prints its arguments on the standard output, or on a
file if >expression is present, or on a pipe if '|cmd' is present. The
output resulted from the print statement is terminated by the output
record separator with each argument separated by the current output field
separator. The printf statement formats its expression list according to
the format (see printf(3C)).

Built-in Functions
The arithmetic functions are as follows:

cos(x)
Return cosine of x, where x is in radians. (In
/usr/xpg4/bin/awk only. See nawk(1).)


sin(x)
Return sine of x, where x is in radians. (In /usr/xpg4/bin/awk
only. See nawk(1).)


exp(x)
Return the exponential function of x.


log(x)
Return the natural logarithm of x.


sqrt(x)
Return the square root of x.


int(x)
Truncate its argument to an integer. It is truncated toward 0
when x > 0.


The string functions are as follows:

index(s, t)

Return the position in string s where string t first occurs, or 0 if
it does not occur at all.


int(s)

truncates s to an integer value. If s is not specified, $0 is used.


length(s)

Return the length of its argument taken as a string, or of the whole
line if there is no argument.


split(s, a, fs)

Split 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.


sprintf(fmt, expr, expr,...)

Format the expressions according to the printf(3C) format given by
fmt and returns the resulting string.


substr(s, m, n)

returns the n-character substring of s that begins at position m.


The input/output function is as follows:

getline
Set $0 to the next input record from the current input file.
getline returns 1 for successful input, 0 for end of file, and
-1 for an error.


Large File Behavior


See largefile(5) for the description of the behavior of awk when
encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

EXAMPLES


Example 1: Printing Lines Longer Than 72 Characters




The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints lines longer than seventy two
characters:


length > 72


Example 2: Printing Fields in Opposite Order




The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints the first two fields in opposite
order:


{ print $2, $1 }


Example 3: Printing Fields in Opposite Order with the Input Fields


Separated


The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints the first two input fields in
opposite order, separated by a comma, blanks or tabs:


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


Example 4: Adding Up the First Column, Printing the Sum and Average




The following example is an awk script that can be executed by an awk -f
examplescript style command. It adds up the first column, and prints the
sum and average:


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


Example 5: Printing Fields in Reverse Order




The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints fields in reverse order:


{ for (i = NF; i > 0; --i) print $i }


Example 6: Printing All lines Between start/stop Pairs




The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints all lines between start/stop
pairs.


/start/, /stop/


Example 7: Printing All Lines Whose First Field is Different from the


Previous One


The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints all lines whose first field is
different from the previous one.


$1 != prev { print; prev = $1 }


Example 8: Printing a File and Filling in Page numbers




The following example is an awk script that can be executed by an awk -f
examplescript style command. It prints a file and fills in page numbers
starting at 5:


/Page/ { $2 = n++; }
{ print }


Example 9: Printing a File and Numbering Its Pages




Assuming this program is in a file named prog, the following example
prints the file input numbering its pages starting at 5:


example% awk -f prog n=5 input


ENVIRONMENT VARIABLES


See environ(5) for descriptions of the following environment variables
that affect the execution of awk: LANG, LC_ALL, LC_COLLATE, LC_CTYPE,
LC_MESSAGES, NLSPATH, and PATH.

LC_NUMERIC
Determine the radix character used when interpreting
numeric input, performing conversions between numeric and
string values and formatting numeric output. Regardless of
locale, the period character (the decimal-point character
of the POSIX locale) is the decimal-point character
recognized in processing awk programs (including
assignments in command-line arguments).


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:

/usr/bin/awk

+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|CSI | Not Enabled |
+---------------+-----------------+

/usr/xpg4/bin/awk

+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|CSI | Enabled |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+

SEE ALSO


egrep(1), grep(1), nawk(1), sed(1), printf(3C), attributes(5),
environ(5), largefile(5), standards(5)

NOTES


Input white space is not preserved on output if fields are involved.


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 an
expression to be treated as a string, concatenate the null string ("") to
it.


June 22, 2005 AWK(1)