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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
-f progfile 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 -F ERE 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
instances of this option are specified, the
concatenation of the files specified as
progfile in the order specified is the nawk
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program. The nawk program can alternatively
be specified in the command line as a single
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, including
the actions associated with BEGIN patterns
(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 pro-
gram. 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 argu-
ment can be intermixed:
file
A pathname of a file that contains the
input to be read, which is matched
against the set of patterns in the pro-
gram. If no file operands are specified,
or if a file operand is -, the standard
input is used.
assignment
An operand that begins with an under-
score or alphabetic character from the
portable character set, followed by a
sequence of underscores, digits and
alphabetics from the portable character
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set, followed by the = character speci-
fies a variable assignment rather than a
pathname. The characters before the =
represent the name of a nawk variable.
If that name is a nawk reserved word,
the behavior is undefined. The charac-
ters following 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 charac-
ter 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 numeric-
string, the variable is assigned its
numeric value. Each such variable
assignment is performed 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 process-
ing 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 {LINE_MAX} bytes and may 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).
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
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--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
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
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converted to a numeric value by the equivalent of the fol-
lowing calls:
setlocale(LC_NUMERIC, "");
numeric_value = atof(string_value);
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 lexically
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.
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 expression.
o an expression operated on by logical NOT, logical AND,
or logical OR.
o
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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 Program
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]
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
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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, exclud-
ing options and the program argument, num-
bered 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, 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 argu-
ment is treated as an assignment rather than
a file argument.
ENVIRON The variable ENVIRON is an array represent-
ing the value of the environment. The
indices of the array are strings consisting
of the names of the environment variables,
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and the value of each array element is a
string consisting of the value of that vari-
able. If the value of an environment vari-
able 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 exe-
cutes via the system function or via pipe-
line redirections with the print statement,
the printf statement, or the getline func-
tion), the environment used is the environ-
ment at the time nawk began executing.
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 pro-
cessed 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
undefined 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, getline function
without a var argument is performed 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
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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 character, the results are unspeci-
fied. 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 beginning
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.
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/usr/xpg4/bin/awk
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 NULL 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
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
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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 expression delim-
its 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
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character 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
characters 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
newline character and the record separator) can be embedded
in the pattern and an appropriate pattern will match any
character. 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
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
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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 may 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
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
output_redirection if one is supplied, as follows:
> expression
>> expression
| expression
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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 will remain
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 expr_list, print_expr_list or print_expr_list_opt.
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
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 cannot contain
empty character positions. The space character in the
format string, in any context other than a flag of a
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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 charac-
ter is treated as sequences of ordinary characters 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 output
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 speci-
fied 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 is not the
encoding of any character in the character set, the
behavior is undefined. If the argument does not have a
numeric value, the first character of the string value
will be output; if the string does not contain any char-
acters the behavior is undefined.
8. For each conversion specification that consumes an argu-
ment, the next expression argument will be evaluated.
With the exception of the c conversion, the value will
be 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
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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 {LINE_MAX} 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.
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 will
be truncated toward 0 when x > 0.
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User Commands nawk(1)
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 pre-
vious seed value will be 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 will replace
all occurrences of the regu-
lar expression (like the ed
utility 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 char-
acters, 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 string s where the
extended regular expression
ere occurs, or zero if it
does not occur at all.
RSTART will be set to the
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User Commands nawk(1)
starting position (which is
the same as the returned
value), zero if no match is
found; RLENGTH will be 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 will be done with
the extended regular expres-
sion fs or with the field
separator FS if fs is not
given. Each array element
will have a string value
when created. If the string
assigned to any array ele-
ment, with any occurrence of
the decimal-point character
from the current locale
changed to a period charac-
ter, would be considered a
numeric string; the array
element will also have 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 for-
mat 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 will be
replaced by the string from
in that matches the regular
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User Commands nawk(1)
expression. For each
occurrence of backslash (\)
encountered when scanning
the string repl from begin-
ning to end, the next char-
acter is taken literally and
loses its special meaning
(for example, \& will be
interpreted as a literal
ampersand character). Except
for & and \, it is unspeci-
fied what the special mean-
ing of any such character
is. If in is specified and
it is not an lvalue the
behavior is undefined. If in
is omitted, nawk will sub-
stitute in the current
record ($0).
substr(s,m[,n]) 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 will be 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
LC_CTYPE category of the
current locale will be
replaced in the returned
string by the lower-case
letter specified by the map-
ping. Other characters in s
will be 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
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User Commands nawk(1)
toupper mapping by the
LC_CTYPE category of the
current locale will be
replaced in the returned
string by the upper-case
letter specified by the map-
ping. Other characters in s
will be 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 get-
line with the same string-
valued expression. If the
close was successful, the
function will return 0; oth-
erwise, it will return non-
zero.
expression|getline[var] Read a record of input from
a stream piped from the out-
put of a command. The stream
will be created if no stream
is currently open with the
value of expression as its
command name. The stream
created will be equivalent
to one created by a call to
the popen function with the
value of expression as the
command argument and a value
of r as the mode argument.
As long as the stream
remains open, subsequent
calls in which expression
evaluates to the same string
value will read subsequent
records from the file. The
stream will remain open
until the close function is
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User Commands nawk(1)
called with an expression
that evaluates to the same
string value. At that time,
the stream will be closed as
if by a call to the pclose
function. If var is missing,
$0 and NF will be set; oth-
erwise, var will be set.
The getline operator can
form ambiguous constructs
when there are operators
that are not in parentheses
(including concatenate) to
the left of the | (to the
beginning of the expression
containing 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 port-
able applications must be
put in parentheses properly.
getline Set $0 to the next input
record from the current
input file. This form of
getline will set the NF, NR,
and FNR variables.
getline var Set variable var to the next
input record from the
current input file. This
form of getline will set the
FNR and NR variables.
getline [var] < expression Read the next record of
input from a named file. The
expression will be evaluated
to produce a string that is
used as a full pathname. If
the file of that name is not
currently open, it will be
opened. As long as the
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User Commands nawk(1)
stream remains open, subse-
quent calls in which expres-
sion evaluates to the same
string value will read sub-
sequent records from the
file. The file will remain
open until the close func-
tion is called with an
expression that evaluates to
the same string value. If
var is missing, $0 and NF
will be set; otherwise, var
will be set.
The getline operator can
form ambiguous constructs
when there are binary opera-
tors that are not in
parentheses (including con-
catenate) 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 applica-
tions must be put in
parentheses properly.
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 will 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:
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User Commands nawk(1)
function name(args,...) { statements }
A function can be referred to anywhere in an nawk program;
in particular, its use can precede its definition. The scope
of a function will be 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 will be passed by value if
scalar and by reference if array name. Argument names will
be local to the function; all other variable names will be
global. The same name will not be used as both an argument
name and as the name of a function or a special nawk vari-
able. 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 will be 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 will be initialized as empty arrays. If more argu-
ments are supplied in a function call than are in the func-
tion 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 will be 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
nawk versions deal with characters, while the ISO C standard
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User Commands nawk(1)
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 reg-
ular expression:
/(G|D)(2[0-9][[:alpha:]]*)/
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.
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User Commands nawk(1)
/(G|D)([[: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:
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:
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User Commands nawk(1)
{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/
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
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User Commands nawk(1)
nawk -f program n=5 input
will print 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: LC_COLLATE, LC_CTYPE,
LC_MESSAGES, and NLSPATH.
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 argu-
ments).
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.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
/usr/bin/nawk
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
/usr/xpg4/bin/awk
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User Commands nawk(1)
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE 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),
largefile(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 will write a diagnostic message to stan-
dard 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.
SunOS 5.10 Last change: 17 Jun 2005 29
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