User Commands nawk(1)
NAME
nawk - pattern scanning and processing language
SYNOPSIS
/usr/bin/nawk [-F ERE] [-v assignment] 'program' -f progfile...
[argument]...
/usr/xpg4/bin/awk [-F ERE] [-v assignment]... 'program' -f progfile...
[argument]...
DESCRIPTION
The /usr/bin/nawk and /usr/xpg4/bin/awk utilities execute
programs written in the nawk programming language, which is
specialized for textual data manipulation. A nawk program is
a sequence of patterns and corresponding actions. The string
specifying program must be enclosed in single quotes (') to
protect it from interpretation by the shell. The sequence of
pattern - action statements can be specified in the command
line as program or in one, or more, file(s) specified by the
-fprogfile option. When input is read that matches a pat-
tern, the action associated with the pattern is performed.
Input is interpreted as a sequence of records. By default, a
record is a line, but this can be changed by using the RS
built-in variable. Each record of input is matched to each
pattern in the program. For each pattern matched, the asso-
ciated action is executed.
The nawk utility interprets each input record as a sequence
of fields where, by default, a field is a string of non-
blank characters. This default white-space field delimiter
(blanks and/or tabs) can be changed by using the FS built-in
variable or the -FERE option. The nawk utility denotes the
first field in a record $1, the second $2, and so forth. The
symbol $0 refers to the entire record; setting any other
field causes the reevaluation of $0. Assigning to $0 resets
the values of all fields and the NF built-in variable.
OPTIONS
The following options are supported:
-F ERE Define the input field separator to be the
extended regular expression ERE, before any
input is read (can be a character).
-f progfile Specifies the pathname of the file progfile
containing a nawk program. If multiple
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instances of this option are specified, the
concatenation of the files specified as
progfile in the order specified is the nawk
program. The nawk program can alternatively
be specified in the command line as a sin-
gle argument.
-v assignment The assignment argument must be in the same
form as an assignment operand. The assign-
ment is of the form var=value, where var is
the name of one of the variables described
below. The specified assignment occurs
before executing the nawk program, includ-
ing the actions associated with BEGIN pat-
terns (if any). Multiple occurrences of
this option can be specified.
OPERANDS
The following operands are supported:
program If no -f option is specified, the first operand
to nawk is the text of the nawk program. The
application supplies the program operand as a
single argument to nawk. If the text does not
end in a newline character, nawk interprets the
text as if it did.
argument Either of the following two types of argument
can be intermixed:
file A pathname of a file that contains
the input to be read, which is
matched against the set of pat-
terns in the program. If no file
operands are specified, or if a
file operand is -, the standard
input is used.
assignment An operand that begins with an
underscore or alphabetic character
from the portable character set,
followed by a sequence of under-
scores, digits and alphabetics
from the portable character set,
followed by the = character speci-
fies a variable assignment rather
than a pathname. The characters
before the = represent the name of
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a nawk variable. If that name is a
nawk reserved word, the behavior
is undefined. The characters fol-
lowing the equal sign is inter-
preted as if they appeared in the
nawk program preceded and followed
by a double-quote (") character,
as a STRING token , except that if
the last character is an unescaped
backslash, it is interpreted as a
literal backslash rather than as
the first character of the
sequence \.. The variable is
assigned the value of that STRING
token. If the value is considered
a numericstring, the variable is
assigned its numeric value. Each
such variable assignment is per-
formed just before the processing
of the following file, if any.
Thus, an assignment before the
first file argument is executed
after the BEGIN actions (if any),
while an assignment after the last
file argument is executed before
the END actions (if any). If
there are no file arguments,
assignments are executed before
processing the standard input.
INPUT FILES
Input files to the nawk program from any of the following
sources:
o any file operands or their equivalents, achieved by
modifying the nawk variables ARGV and ARGC
o standard input in the absence of any file operands
o arguments to the getline function
must be text files. Whether the variable RS is set to a
value other than a newline character or not, for these
files, implementations support records terminated with the
specified separator up to {LINEMAX} bytes and can support
longer records.
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If -f progfile is specified, the files named by each of the
progfile option-arguments must be text files containing an
nawk program.
The standard input are used only if no file operands are
specified, or if a file operand is -.
EXTENDED DESCRIPTION
A nawk program is composed of pairs of the form:
pattern { action }
Either the pattern or the action (including the enclosing
brace characters) can be omitted. Pattern-action statements
are separated by a semicolon or by a newline.
A missing pattern matches any record of input, and a missing
action is equivalent to an action that writes the matched
record of input to standard output.
Execution of the nawk program starts by first executing the
actions associated with all BEGIN patterns in the order they
occur in the program. Then each file operand (or standard
input if no files were specified) is processed by reading
data from the file until a record separator is seen (a new-
line character by default), splitting the current record
into fields using the current value of FS, evaluating each
pattern in the program in the order of occurrence, and exe-
cuting the action associated with each pattern that matches
the current record. The action for a matching pattern is
executed before evaluating subsequent patterns. Last, the
actions associated with all END patterns is executed in the
order they occur in the program.
Expressions in nawk
Expressions describe computations used in patterns and
actions. In the following table, valid expression operations
are given in groups from highest precedence first to lowest
precedence last, with equal-precedence operators grouped
between horizontal lines. In expression evaluation, where
the grammar is formally ambiguous, higher precedence opera-
tors are evaluated before lower precedence operators. In
this table expr, expr1, expr2, and expr3 represent any
expression, while lvalue represents any entity that can be
assigned to (that is, on the left side of an assignment
operator).
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Syntax Name Type of Result Associativity
( expr ) Grouping type of expr n/a
$expr Field reference string n/a
] lvalue Pre-increment numeric n/a
--lvalue Pre-decrement numeric n/a
lvalue ] Post-increment numeric n/a
lvalue -- Post-decrement numeric n/a
expr ^ expr Exponentiation numeric right
! expr Logical not numeric n/a
] expr Unary plus numeric n/a
- expr Unary minus numeric n/a
expr * expr Multiplication numeric left
expr / expr Division numeric left
expr % expr Modulus numeric left
expr ] expr Addition numeric left
expr - expr Subtraction numeric left
expr expr String concatenation string left
expr < expr Less than numeric none
expr <= expr Less than or equal to numeric none
expr != expr Not equal to numeric none
expr == expr Equal to numeric none
expr > expr Greater than numeric none
expr >= expr Greater than or equal to numeric none
expr ~ expr ERE match numeric none
expr !~ expr ERE non-match numeric none
expr in array Array membership numeric left
( index ) in Multi-dimension array numeric left
array membership
expr && expr Logical AND numeric left
expr expr Logical OR numeric left
expr1 ? expr2 Conditional expression type of selected right
: expr3 expr2 or expr3
lvalue ^= expr Exponentiation numeric right
assignment
lvalue %= expr Modulus assignment numeric right
lvalue *= expr Multiplication numeric right
assignment
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lvalue /= expr Division assignment numeric right
lvalue ]= expr Addition assignment numeric right
lvalue -= expr Subtraction assignment numeric right
lvalue = expr Assignment type of expr right
Each expression has either a string value, a numeric value
or both. Except as stated for specific contexts, the value
of an expression is implicitly converted to the type needed
for the context in which it is used. A string value is con-
verted to a numeric value by the equivalent of the following
calls:
setlocale(LCNUMERIC, "");
numericvalue = atof(stringvalue);
A numeric value that is exactly equal to the value of an
integer is converted to a string by the equivalent of a call
to the sprintf function with the string %d as the fmt argu-
ment and the numeric value being converted as the first and
only expr argument. Any other numeric value is converted to
a string by the equivalent of a call to the sprintf function
with the value of the variable CONVFMT as the fmt argument
and the numeric value being converted as the first and only
expr argument.
A string value is considered to be a numeric string in the
following case:
1. Any leading and trailing blank characters is
ignored.
2. If the first unignored character is a ] or -, it is
ignored.
3. If the remaining unignored characters would be lex-
ically recognized as a NUMBER token, the string is
considered a numeric string.
If a - character is ignored in the above steps, the numeric
value of the numeric string is the negation of the numeric
value of the recognized NUMBER token. Otherwise the numeric
value of the numeric string is the numeric value of the
recognized NUMBER token. Whether or not a string is a
numeric string is relevant only in contexts where that term
is used in this section.
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When an expression is used in a Boolean context, if it has a
numeric value, a value of zero is treated as false and any
other value is treated as true. Otherwise, a string value of
the null string is treated as false and any other value is
treated as true. A Boolean context is one of the following:
o the first subexpression of a conditional expres-
sion.
o an expression operated on by logical NOT, logical
AND, or logical OR.
o the second expression of a for statement.
o the expression of an if statement.
o the expression of the while clause in either a
while or do ... while statement.
o an expression used as a pattern (as in Overall Pro-
gram Structure).
The nawk language supplies arrays that are used for storing
numbers or strings. Arrays need not be declared. They are
initially empty, and their sizes changes dynamically. The
subscripts, or element identifiers, are strings, providing a
type of associative array capability. An array name followed
by a subscript within square brackets can be used as an
lvalue and as an expression, as described in the grammar.
Unsubscripted array names are used in only the following
contexts:
o a parameter in a function definition or function
call.
o the NAME token following any use of the keyword in.
A valid array index consists of one or more comma-separated
expressions, similar to the way in which multi-dimensional
arrays are indexed in some programming languages. Because
nawk arrays are really one-dimensional, such a comma-
separated list is converted to a single string by con-
catenating the string values of the separate expressions,
each separated from the other by the value of the SUBSEP
variable.
Thus, the following two index operations are equivalent:
var[expr1, expr2, ... exprn]
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var[expr1 SUBSEP expr2 SUBSEP ... SUBSEP exprn]
A multi-dimensioned index used with the in operator must be
put in parentheses. The in operator, which tests for the
existence of a particular array element, does not create the
element if it does not exist. Any other reference to a
non-existent array element automatically creates it.
Variables and Special Variables
Variables can be used in an nawk program by referencing
them. With the exception of function parameters, they are
not explicitly declared. Uninitialized scalar variables and
array elements have both a numeric value of zero and a
string value of the empty string.
Field variables are designated by a $ followed by a number
or numerical expression. The effect of the field number
expression evaluating to anything other than a non-negative
integer is unspecified. Uninitialized variables or string
values need not be converted to numeric values in this con-
text. New field variables are created by assigning a value
to them. References to non-existent fields (that is, fields
after $NF) produce the null string. However, assigning to a
non-existent field (for example, $(NF]2) = 5) increases the
value of NF, create any intervening fields with the null
string as their values and cause the value of $0 to be
recomputed, with the fields being separated by the value of
OFS. Each field variable has a string value when created. If
the string, with any occurrence of the decimal-point charac-
ter from the current locale changed to a period character,
is considered a numeric string (see Expressions in nawk
above), the field variable also has the numeric value of the
numeric string.
/usr/bin/nawk, /usr/xpg4/bin/awk
nawk sets the following special variables that are supported
by both /usr/bin/nawk and /usr/xpg4/bin/awk:
ARGC The number of elements in the ARGV array.
ARGV An array of command line arguments, excluding
options and the program argument, numbered from
zero to ARGC-1.
The arguments in ARGV can be modified or added
to; ARGC can be altered. As each input file
ends, nawk treats the next non-null element of
ARGV, up to the current value of ARGC-1,
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inclusive, as the name of the next input file.
Setting an element of ARGV to null means that it
is not treated as an input file. The name -
indicates the standard input. If an argument
matches the format of an assignment operand,
this argument is treated as an assignment rather
than a file argument.
ENVIRON The variable ENVIRON is an array representing
the value of the environment. The indices of the
array are strings consisting of the names of the
environment variables, and the value of each
array element is a string consisting of the
value of that variable. If the value of an
environment variable is considered a numeric
string, the array element also has its numeric
value.
In all cases where nawk behavior is affected by
environment variables (including the environment
of any commands that nawk executes via the sys-
tem function or via pipeline redirections with
the print statement, the printf statement, or
the getline function), the environment used is
the environment at the time nawk began execut-
ing.
FILENAME A pathname of the current input file. Inside a
BEGIN action the value is undefined. Inside an
END action the value is the name of the last
input file processed.
FNR The ordinal number of the current record in the
current file. Inside a BEGIN action the value is
zero. Inside an END action the value is the
number of the last record processed in the last
file processed.
FS Input field separator regular expression; a
space character by default.
NF The number of fields in the current record.
Inside a BEGIN action, the use of NF is unde-
fined unless a getline function without a var
argument is executed previously. Inside an END
action, NF retains the value it had for the last
record read, unless a subsequent, redirected,
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getline function without a var argument is per-
formed prior to entering the END action.
NR The ordinal number of the current record from
the start of input. Inside a BEGIN action the
value is zero. Inside an END action the value is
the number of the last record processed.
OFMT The printf format for converting numbers to
strings in output statements "%.6g" by default.
The result of the conversion is unspecified if
the value of OFMT is not a floating-point format
specification.
OFS The print statement output field separator; a
space character by default.
ORS The print output record separator; a newline
character by default.
LENGTH The length of the string matched by the match
function.
RS The first character of the string value of RS is
the input record separator; a newline character
by default. If RS contains more than one charac-
ter, the results are unspecified. If RS is null,
then records are separated by sequences of one
or more blank lines. Leading or trailing blank
lines do not produce empty records at the begin-
ning or end of input, and the field separator is
always newline, no matter what the value of FS.
RSTART The starting position of the string matched by
the match function, numbering from 1. This is
always equivalent to the return value of the
match function.
SUBSEP The subscript separator string for multi-
dimensional arrays. The default value is \034.
/usr/xpg4/bin/awk
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The following variable is supported for /usr/xpg4/bin/awk
only:
CONVFMT The printf format for converting numbers to
strings (except for output statements, where OFMT
is used). The default is %.6g.
Regular Expressions
The nawk utility makes use of the extended regular expres-
sion notation (see regex(5)) except that it allows the use
of C-language conventions to escape special characters
within the EREs, namely \\, \a, \b, \f, \n, \r, \t, \v, and
those specified in the following table. These escape
sequences are recognized both inside and outside bracket
expressions. Note that records need not be separated by
newline characters and string constants can contain newline
characters, so even the \n sequence is valid in nawk EREs.
Using a slash character within the regular expression
requires escaping as shown in the table below:
Escape Sequence Description Meaning
\" Backslash quotation-mark Quotation-mark character
\/ Backslash slash Slash character
\ddd A backslash character The character encoded by
followed by the longest the one-, two- or
sequence of one, two, or three-digit octal
three octal-digit char- integer. Multi-byte
acters (01234567). If characters require mul-
all of the digits are 0, tiple, concatenated
(that is, representation escape sequences,
of the NUL character), including the leading \
the behavior is unde- for each byte.
fined.
\c A backslash character Undefined
followed by any charac-
ter not described in
this table or special
characters (\\, \a, \b,
\f, \n, \r, \t, \v).
A regular expression can be matched against a specific field
or string by using one of the two regular expression match-
ing operators, ~ and !~. These operators interpret their
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right-hand operand as a regular expression and their left-
hand operand as a string. If the regular expression matches
the string, the ~ expression evaluates to the value 1, and
the !~ expression evaluates to the value 0. If the regular
expression does not match the string, the ~ expression
evaluates to the value 0, and the !~ expression evaluates to
the value 1. If the right-hand operand is any expression
other than the lexical token ERE, the string value of the
expression is interpreted as an extended regular expression,
including the escape conventions described above. Notice
that these same escape conventions also are applied in the
determining the value of a string literal (the lexical token
STRING), and is applied a second time when a string literal
is used in this context.
When an ERE token appears as an expression in any context
other than as the right-hand of the ~ or !~ operator or as
one of the built-in function arguments described below, the
value of the resulting expression is the equivalent of:
$0 ~ /ere/
The ere argument to the gsub, match, sub functions, and the
fs argument to the split function (see String Functions) is
interpreted as extended regular expressions. These can be
either ERE tokens or arbitrary expressions, and are inter-
preted in the same manner as the right-hand side of the ~ or
!~ operator.
An extended regular expression can be used to separate
fields by using the -F ERE option or by assigning a string
containing the expression to the built-in variable FS. The
default value of the FS variable is a single space charac-
ter. The following describes FS behavior:
1. If FS is a single character:
o If FS is the space character, skip leading and
trailing blank characters; fields are delimited
by sets of one or more blank characters.
o Otherwise, if FS is any other character c,
fields are delimited by each single occurrence
of c.
2. Otherwise, the string value of FS is considered to
be an extended regular expression. Each occurrence
of a sequence matching the extended regular
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expression delimits fields.
Except in the gsub, match, split, and sub built-in func-
tions, regular expression matching is based on input
records. That is, record separator characters (the first
character of the value of the variable RS, a newline charac-
ter by default) cannot be embedded in the expression, and no
expression matches the record separator character. If the
record separator is not a newline character, newline charac-
ters embedded in the expression can be matched. In those
four built-in functions, regular expression matching are
based on text strings. So, any character (including the new-
line character and the record separator) can be embedded in
the pattern and an appropriate pattern matches any charac-
ter. However, in all nawk regular expression matching, the
use of one or more NUL characters in the pattern, input
record or text string produces undefined results.
Patterns
A pattern is any valid expression, a range specified by two
expressions separated by comma, or one of the two special
patterns BEGIN or END.
Special Patterns
The nawk utility recognizes two special patterns, BEGIN and
END. Each BEGIN pattern is matched once and its associated
action executed before the first record of input is read
(except possibly by use of the getline function in a prior
BEGIN action) and before command line assignment is done.
Each END pattern is matched once and its associated action
executed after the last record of input has been read. These
two patterns have associated actions.
BEGIN and END do not combine with other patterns. Multiple
BEGIN and END patterns are allowed. The actions associated
with the BEGIN patterns are executed in the order specified
in the program, as are the END actions. An END pattern can
precede a BEGIN pattern in a program.
If an nawk program consists of only actions with the pattern
BEGIN, and the BEGIN action contains no getline function,
nawk exits without reading its input when the last statement
in the last BEGIN action is executed. If an nawk program
consists of only actions with the pattern END or only
actions with the patterns BEGIN and END, the input is read
before the statements in the END actions are executed.
Expression Patterns
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An expression pattern is evaluated as if it were an expres-
sion in a Boolean context. If the result is true, the pat-
tern is considered to match, and the associated action (if
any) is executed. If the result is false, the action is not
executed.
Pattern Ranges
A pattern range consists of two expressions separated by a
comma. In this case, the action is performed for all records
between a match of the first expression and the following
match of the second expression, inclusive. At this point,
the pattern range can be repeated starting at input records
subsequent to the end of the matched range.
Actions
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
delete array[subscript] #delete an array element
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
return [expr]
Any single statement can be replaced by a statement list
enclosed in braces. The statements are terminated by new-
line characters or semicolons, and are executed sequentially
in the order that they appear.
The next statement causes all further processing of the
current input record to be abandoned. The behavior is unde-
fined if a next statement appears or is invoked in a BEGIN
or END action.
The exit statement invokes all END actions in the order in
which they occur in the program source and then terminate
the program without reading further input. An exit statement
inside an END action terminates the program without further
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execution of END actions. If an expression is specified in
an exit statement, its numeric value is the exit status of
nawk, unless subsequent errors are encountered or a subse-
quent exit statement with an expression is executed.
Output Statements
Both print and printf statements write to standard output by
default. The output is written to the location specified by
outputredirection if one is supplied, as follows:
> expression>> expression expression
In all cases, the expression is evaluated to produce a
string that is used as a full pathname to write into (for >
or >>) or as a command to be executed (for ). Using the
first two forms, if the file of that name is not currently
open, it is opened, creating it if necessary and using the
first form, truncating the file. The output then is appended
to the file. As long as the file remains open, subsequent
calls in which expression evaluates to the same string value
simply appends output to the file. The file remains open
until the close function, which is called with an expression
that evaluates to the same string value.
The third form writes output onto a stream piped to the
input of a command. The stream is created if no stream is
currently open with the value of expression as its command
name. The stream created is equivalent to one created by a
call to the popen(3C) function with the value of expression
as the command argument and a value of w as the mode argu-
ment. As long as the stream remains open, subsequent calls
in which expression evaluates to the same string value
writes output to the existing stream. The stream remains
open until the close function is called with an expression
that evaluates to the same string value. At that time, the
stream is closed as if by a call to the pclose function.
These output statements take a comma-separated list of
expression s referred in the grammar by the non-terminal
symbols exprlist, printexprlist or printexprlistopt.
This list is referred to here as the expression list, and
each member is referred to as an expression argument.
The print statement writes the value of each expression
argument onto the indicated output stream separated by the
current output field separator (see variable OFS above), and
terminated by the output record separator (see variable ORS
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above). All expression arguments is taken as strings, being
converted if necessary; with the exception that the printf
format in OFMT is used instead of the value in CONVFMT. An
empty expression list stands for the whole input record
($0).
The printf statement produces output based on a notation
similar to the File Format Notation used to describe file
formats in this document Output is produced as specified
with the first expression argument as the string format and
subsequent expression arguments as the strings arg1 to argn,
inclusive, with the following exceptions:
1. The format is an actual character string rather
than a graphical representation. Therefore, it can-
not contain empty character positions. The space
character in the format string, in any context
other than a flag of a conversion specification, is
treated as an ordinary character that is copied to
the output.
2. If the character set contains a Delta character and
that character appears in the format string, it is
treated as an ordinary character that is copied to
the output.
3. The escape sequences beginning with a backslash
character is treated as sequences of ordinary char-
acters that are copied to the output. Note that
these same sequences is interpreted lexically by
nawk when they appear in literal strings, but they
is not treated specially by the printf statement.
4. A field width or precision can be specified as the
* character instead of a digit string. In this case
the next argument from the expression list is
fetched and its numeric value taken as the field
width or precision.
5. The implementation does not precede or follow out-
put from the d or u conversion specifications with
blank characters not specified by the format
string.
6. The implementation does not precede output from the
o conversion specification with leading zeros not
specified by the format string.
7. For the c conversion specification: if the argument
has a numeric value, the character whose encoding
is that value is output. If the value is zero or
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is not the encoding of any character in the charac-
ter set, the behavior is undefined. If the argu-
ment does not have a numeric value, the first char-
acter of the string value is output; if the string
does not contain any characters the behavior is
undefined.
8. For each conversion specification that consumes an
argument, the next expression argument is
evaluated. With the exception of the c conversion,
the value is converted to the appropriate type for
the conversion specification.
9. If there are insufficient expression arguments to
satisfy all the conversion specifications in the
format string, the behavior is undefined.
10. If any character sequence in the format string
begins with a % character, but does not form a
valid conversion specification, the behavior is
unspecified.
Both print and printf can output at least {LINEMAX} bytes.
Functions
The nawk language has a variety of built-in functions:
arithmetic, string, input/output and general.
Arithmetic Functions
The arithmetic functions, except for int, are based on the
ISO C standard. The behavior is undefined in cases where the
ISO C standard specifies that an error be returned or that
the behavior is undefined. Although the grammar permits
built-in functions to appear with no arguments or
parentheses, unless the argument or parentheses are indi-
cated as optional in the following list (by displaying them
within the [ ] brackets), such use is undefined.
atan2(y,x) Return arctangent of y/x.
cos(x) Return cosine of x, where x is in radians.
sin(x) Return sine of x, where x is in radians.
exp(x) Return the exponential function of x.
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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.
rand() Return a random number n, such that 0 < n <
1.
srand([expr]) Set the seed value for rand to expr or use
the time of day if expr is omitted. The
previous seed value is returned.
String Functions
The string functions in the following list shall be sup-
ported. Although the grammar permits built-in functions to
appear with no arguments or parentheses, unless the argument
or parentheses are indicated as optional in the following
list (by displaying them within the [ ] brackets), such use
is undefined.
gsub(ere,repl[,in])
Behave like sub (see below), except that it replaces all
occurrences of the regular expression (like the ed util-
ity global substitute) in $0 or in the in argument, when
specified.
index(s,t)
Return the position, in characters, numbering from 1, in
string s where string t first occurs, or zero if it does
not occur at all.
length[([s])]
Return the length, in characters, of its argument taken
as a string, or of the whole record, $0, if there is no
argument.
match(s,ere)
Return the position, in characters, numbering from 1, in
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string s where the extended regular expression ere
occurs, or zero if it does not occur at all. RSTART is
set to the starting position (which is the same as the
returned value), zero if no match is found; RLENGTH is
set to the length of the matched string, -1 if no match
is found.
split(s,a[,fs])
Split the string s into array elements a[1], a[2], ...,
a[n], and return n. The separation is done with the
extended regular expression fs or with the field separa-
tor FS if fs is not given. Each array element has a
string value when created. If the string assigned to any
array element, with any occurrence of the decimal-point
character from the current locale changed to a period
character, would be considered a numeric string; the
array element also has the numeric value of the numeric
string. The effect of a null string as the value of fs
is unspecified.
sprintf(fmt,expr,expr,...)
Format the expressions according to the printf format
given by fmt and return the resulting string.
sub(ere,repl[,in])
Substitute the string repl in place of the first
instance of the extended regular expression ERE in
string in and return the number of substitutions. An
ampersand ( & ) appearing in the string repl is replaced
by the string from in that matches the regular expres-
sion. An ampersand preceded with a backslash ( \ ) is
interpreted as the literal ampersand character. An
occurrence of two consecutive backslashes is interpreted
as just a single literal backslash character. Any other
occurrence of a backslash (for example, preceding any
other character) is treated as a literal backslash char-
acter. If repl is a string literal, the handling of the
ampersand character occurs after any lexical processing,
including any lexical backslash escape sequence process-
ing. If in is specified and it is not an lvalue the
behavior is undefined. If in is omitted, nawk uses the
current record ($0) in its place.
substr(s,m[,n])
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Return the at most n-character substring of s that
begins at position m, numbering from 1. If n is missing,
the length of the substring is limited by the length of
the string s.
tolower(s)
Return a string based on the string s. Each character in
s that is an upper-case letter specified to have a
tolower mapping by the LCTYPE category of the current
locale is replaced in the returned string by the lower-
case letter specified by the mapping. Other characters
in s are unchanged in the returned string.
toupper(s)
Return a string based on the string s. Each character in
s that is a lower-case letter specified to have a
toupper mapping by the LCTYPE category of the current
locale is replaced in the returned string by the upper-
case letter specified by the mapping. Other characters
in s are unchanged in the returned string.
All of the preceding functions that take ERE as a parameter
expect a pattern or a string valued expression that is a
regular expression as defined below.
Input/Output and General Functions
The input/output and general functions are:
close(expression) Close the file or pipe opened by
a print or printf statement or a
call to getline with the same
string-valued expression. If the
close was successful, the func-
tion returns 0; otherwise, it
returns non-zero.
expressiongetline[var] Read a record of input from a
stream piped from the output of a
command. The stream is created if
no stream is currently open with
the value of expression as its
command name. The stream created
is equivalent to one created by a
call to the popen function with
the value of expression as the
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command argument and a value of r
as the mode argument. As long as
the stream remains open, subse-
quent calls in which expression
evaluates to the same string
value reads subsequent records
from the file. The stream remains
open until the close function is
called with an expression that
evaluates to the same string
value. At that time, the stream
is closed as if by a call to the
pclose function. If var is miss-
ing, $0 and NF is set. Otherwise,
var is set.
The getline operator can form
ambiguous constructs when there
are operators that are not in
parentheses (including concaten-
ate) to the left of the (to the
beginning of the expression con-
taining getline). In the context
of the $ operator, behaves as
if it had a lower precedence than
$. The result of evaluating other
operators is unspecified, and all
such uses of portable applica-
tions must be put in parentheses
properly.
getline Set $0 to the next input
record from the current input
file. This form of getline
sets the NF, NR, and FNR vari-
ables.
getline var Set variable var to the next
input record from the current
input file. This form of get-
line sets the FNR and NR vari-
ables.
getline [var] < expression Read the next record of input
from a named file. The expres-
sion is evaluated to produce a
string that is used as a full
pathname. If the file of that
name is not currently open, it
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is opened. As long as the
stream remains open, subse-
quent calls in which expres-
sion evaluates to the same
string value reads subsequent
records from the file. The
file remains open until the
close function is called with
an expression that evaluates
to the same string value. If
var is missing, $0 and NF is
set. Otherwise, var is set.
The getline operator can form
ambiguous constructs when
there are binary operators
that are not in parentheses
(including concatenate) to the
right of the < (up to the end
of the expression containing
the getline). The result of
evaluating such a construct is
unspecified, and all such uses
of portable applications must
be put in parentheses prop-
erly.
system(expression) Execute the command given by
expression in a manner
equivalent to the system(3C)
function and return the exit
status of the command.
All forms of getline return 1 for successful input, 0 for
end of file, and -1 for an error.
Where strings are used as the name of a file or pipeline,
the strings must be textually identical. The terminology
``same string value'' implies that ``equivalent strings'',
even those that differ only by space characters, represent
different files.
User-defined Functions
The nawk language also provides user-defined functions. Such
functions can be defined as:
function name(args,...) { statements }
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A function can be referred to anywhere in an nawk program;
in particular, its use can precede its definition. The scope
of a function is global.
Function arguments can be either scalars or arrays; the
behavior is undefined if an array name is passed as an argu-
ment that the function uses as a scalar, or if a scalar
expression is passed as an argument that the function uses
as an array. Function arguments are passed by value if
scalar and by reference if array name. Argument names are
local to the function; all other variable names are global.
The same name is not used as both an argument name and as
the name of a function or a special nawk variable. The same
name must not be used both as a variable name with global
scope and as the name of a function. The same name must not
be used within the same scope both as a scalar variable and
as an array.
The number of parameters in the function definition need not
match the number of parameters in the function call. Excess
formal parameters can be used as local variables. If fewer
arguments are supplied in a function call than are in the
function definition, the extra parameters that are used in
the function body as scalars are initialized with a string
value of the null string and a numeric value of zero, and
the extra parameters that are used in the function body as
arrays are initialized as empty arrays. If more arguments
are supplied in a function call than are in the function
definition, the behavior is undefined.
When invoking a function, no white space can be placed
between the function name and the opening parenthesis. Func-
tion calls can be nested and recursive calls can be made
upon functions. Upon return from any nested or recursive
function call, the values of all of the calling function's
parameters are unchanged, except for array parameters passed
by reference. The return statement can be used to return a
value. If a return statement appears outside of a function
definition, the behavior is undefined.
In the function definition, newline characters are optional
before the opening brace and after the closing brace. Func-
tion definitions can appear anywhere in the program where a
pattern-action pair is allowed.
USAGE
The index, length, match, and substr functions should not be
confused with similar functions in the ISO C standard; the
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nawk versions deal with characters, while the ISO C standard
deals with bytes.
Because the concatenation operation is represented by adja-
cent expressions rather than an explicit operator, it is
often necessary to use parentheses to enforce the proper
evaluation precedence.
See largefile(5) for the description of the behavior of nawk
when encountering files greater than or equal to 2 Gbyte
(2^31 bytes).
EXAMPLES
The nawk program specified in the command line is most
easily specified within single-quotes (for example, 'pro-
gram') for applications using sh, because nawk programs com-
monly contain characters that are special to the shell,
including double-quotes. In the cases where a nawk program
contains single-quote characters, it is usually easiest to
specify most of the program as strings within single-quotes
concatenated by the shell with quoted single-quote charac-
ters. For example:
nawk '/'\''/ { print "quote:", $0 }'
prints all lines from the standard input containing a
single-quote character, prefixed with quote:.
The following are examples of simple nawk programs:
Example 1 Write to the standard output all input lines for
which field 3 is greater than 5:
$3 > 5
Example 2 Write every tenth line:
(NR % 10) == 0
Example 3 Write any line with a substring matching the regu-
lar expression:
/(GD)(2[0-9][:alpha:]*)/
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Example 4 Print any line with a substring containing a G or
D, followed by a sequence of digits and characters:
This example uses character classes digit and alpha to match
language-independent digit and alphabetic characters,
respectively.
/(GD)([:digit:][:alpha:]*)/
Example 5 Write any line in which the second field matches
the regular expression and the fourth field does not:
$2 ~ /xyz/ && $4 !~ /xyz/
Example 6 Write any line in which the second field contains
a backslash:
$2 ~ /\\/
Example 7 Write any line in which the second field contains
a backslash (alternate method):
Notice that backslash escapes are interpreted twice, once in
lexical processing of the string and once in processing the
regular expression.
$2 ~ "\\\\"
Example 8 Write the second to the last and the last field in
each line, separating the fields by a colon:
{OFS=":";print $(NF-1), $NF}
Example 9 Write the line number and number of fields in each
line:
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The three strings representing the line number, the colon
and the number of fields are concatenated and that string is
written to standard output.
{print NR ":" NF}
Example 10 Write lines longer than 72 characters:
{length($0) > 72}
Example 11 Write first two fields in opposite order
separated by the OFS:
{ print $2, $1 }
Example 12 Same, with input fields separated by comma or
space and tab characters, or both:
BEGIN { FS = ",[\t]*[\t]" }
{ print $2, $1 }
Example 13 Add up first column, print sum and average:
{s ]= $1 }
END {print "sum is ", s, " average is", s/NR}
Example 14 Write fields in reverse order, one per line (many
lines out for each line in):
{ for (i = NF; i > 0; --i) print $i }
Example 15 Write all lines between occurrences of the
strings "start" and "stop":
/start/, /stop/
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Example 16 Write all lines whose first field is different
from the previous one:
$1 != prev { print; prev = $1 }
Example 17 Simulate the echo command:
BEGIN {
for (i = 1; i < ARGC; ]i)
printf "%s%s", ARGV[i], i==ARGC-1?"\n":""
}
Example 18 Write the path prefixes contained in the PATH
environment variable, one per line:
BEGIN {
n = split (ENVIRON["PATH"], path, ":")
for (i = 1; i <= n; ]i)
print path[i]
}
Example 19 Print the file "input", filling in page numbers
starting at 5:
If there is a file named input containing page headers of
the form
Page#
and a file named program that contains
/Page/{ $2 = n]; }
{ print }
then the command line
nawk -f program n=5 input
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prints the file input, filling in page numbers starting at
5.
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment
variables that affect execution: LCOLATE, LCTYPE,
LCMESAGES, and NLSPATH.
LCNUMERIC Determine the radix character used when inter-
preting numeric input, performing conversions
between numeric and string values and format-
ting 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 pro-
grams (including assignments in command-line
arguments).
EXIT STATUS
The following exit values are returned:
0 All input files were processed successfully.
>0 An error occurred.
The exit status can be altered within the program by using
an exit expression.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
/usr/bin/nawk
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWcsu
/usr/xpg4/bin/awk
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ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWxcu4
SEE ALSO
awk(1), ed(1), egrep(1), grep(1), lex(1), sed(1), popen(3C),
printf(3C), system(3C), attributes(5), environ(5), large-
file(5), regex(5), XPG4(5)
Aho, A. V., B. W. Kernighan, and P. J. Weinberger, The AWK
Programming Language, Addison-Wesley, 1988.
DIAGNOSTICS
If any file operand is specified and the named file cannot
be accessed, nawk writes a diagnostic message to standard
error and terminate without any further action.
If the program specified by either the program operand or a
progfile operand is not a valid nawk program (as specified
in EXTENDED DESCRIPTION), the behavior is undefined.
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 it to be treated as a string concaten-
ate the null string ("") to it.
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