nawk(1) User Commands nawk(1)NAMEnawk - 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 prog‐
file... [argument...]
DESCRIPTION
The /usr/bin/nawk and /usr/xpg4/bin/awk utilities execute programs
written in the nawk programming language, which is specialized for tex‐
tual 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 pattern, 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 associated 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 util‐
ity 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 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 assignment is of the form
var=value, where var is the name of one of the vari‐
ables described below. The specified assignment occurs
before executing the nawk program, including the
actions associated with BEGIN patterns (if any). Multi‐
ple 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 sup‐
plies 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 patterns
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 alpha‐
betic character from the portable character set,
followed by a sequence of underscores, digits and
alphabetics from the portable character set, fol‐
lowed by the = character specifies 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 characters following the equal
sign is interpreted 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 vari‐
able is assigned the value of that STRING token. If
the value is considered a numericstring, the vari‐
able is assigned its numeric value. Each such vari‐
able assignment is performed just before the pro‐
cessing of the following file, if any. Thus, an
assignment before the first file argument is exe‐
cuted 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:
· any file operands or their equivalents, achieved by modifying the
nawk variables ARGV and ARGC
· standard input in the absence of any file operands
· 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 sup‐
port records terminated with the specified separator up to {LINE_MAX}
bytes and may support longer records.
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 charac‐
ters) 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 pro‐
gram. Then each file operand (or standard input if no files were speci‐
fied) is processed by reading data from the file until a record separa‐
tor is seen (a newline character by default), splitting the current
record into fields using the current value of FS, evaluating each pat‐
tern in the program in the order of occurrence, and executing the
action associated with each pattern that matches the current record.
The action for a matching pattern is executed before evaluating subse‐
quent 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-prece‐
dence operators grouped between horizontal lines. In expression evalua‐
tion, 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
−−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 converted to a numeric value by the equivalent
of the following 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 func‐
tion with the string %d as the fmt argument 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 recog‐
nized 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 con‐
text is one of the following:
· the first subexpression of a conditional expression.
· an expression operated on by logical NOT, logical AND, or logical
OR.
· the second expression of a for statement.
· the expression of an if statement.
· the expression of the while clause in either a while or do ...
while statement.
· 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 identi‐
fiers, 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:
· a parameter in a function definition or function call.
· the NAME token following any use of the keyword in.
A valid array index consists of one or more comma-separated expres‐
sions, 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 concatenating 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 par‐
ticular array element, does not create the element if it does not
exist. Any other reference to a non-existent array element automati‐
cally 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. Uninitial‐
ized variables or string values need not be converted to numeric values
in this context. 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 inter‐
vening 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 character 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, 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 envi‐
ronment variables (including the environment of any
commands that nawk executes via the system function or
via pipeline redirections with the print statement, the
printf statement, or the getline function), the envi‐
ronment used is the environment 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 processed in the last file processed.
FS Input field separator regular expression; a space char‐
acter by default.
NF The number of fields in the current record. Inside a
BEGIN action, the use of NF is undefined unless a get‐
line function without a var argument is executed previ‐
ously. 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 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
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 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 equiv‐
alent 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
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 expression 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 expres‐
sions. 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 three-
sequence of one, two, or digit octal integer.
three octal-digit char‐ Multi-byte characters
acters (01234567). If require multiple, con‐
all of the digits are 0, catenated escape
(that is, representation sequences, including the
of the NULL character), leading \ for each byte.
the behavior is unde‐
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 matching 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 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 func‐
tion 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 interpreted 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 character. The following describes FS behavior:
1. If FS is a single character:
· If FS is the space character, skip leading and trailing blank
characters; fields are delimited by sets of one or more blank
characters.
· Otherwise, if FS is any other character c, fields are delim‐
ited 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 delimits fields.
Except in the gsub, match, split, and sub built-in functions, regular
expression matching is based on input records. That is, record separa‐
tor characters (the first character of the value of the variable RS, a
newline 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, regu‐
lar 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 char‐
acter. However, in all nawk regular expression matching, the use of one
or more NUL characters in the pattern, input record or text string pro‐
duces 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 get‐
line function in a prior BEGIN action) and before command line assign‐
ment 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 pat‐
terns 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 read‐
ing its input when the last statement in the last BEGIN action is exe‐
cuted. 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 expression in a
Boolean context. If the result is true, the pattern 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 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 newline characters or semi‐
colons, 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 undefined 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 termi‐
nates 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 sub‐
sequent 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
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 out‐
put 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 com‐
mand. The stream is created if no stream is currently open with the
value of expression as its command name. The stream created is equiva‐
lent 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
argument. 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 func‐
tion 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 sepa‐
rator (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 posi‐
tions. 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 charac‐
ter that is copied to the output.
3. The escape sequences beginning with a backslash character 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 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 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 characters the behav‐
ior is undefined.
8. For each conversion specification that consumes an argument, 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 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 stan‐
dard. The behavior is undefined in cases where the ISO C standard spec‐
ifies that an error be returned or that the behavior is undefined.
Although the grammar permits built-in functions to appear with no argu‐
ments 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.
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 trun‐
cated 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 will be
returned.
String Functions
The string functions in the following list shall be supported. 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 regular 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 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 string s where the
extended regular expression ere occurs,
or zero if it does not occur at all.
RSTART will be set to the 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 expression 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 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 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 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 reg‐
ular 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
expression. For each occurrence of
backslash (\) encountered when scanning
the string repl from beginning to end,
the next character is taken literally
and loses its special meaning (for
example, \& will be interpreted as a
literal ampersand character). Except
for & and \, it is unspecified what the
special meaning 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 substitute in the
current record ($0).
substr(s,m[,n]) Return the at most n-character sub‐
string 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 let‐
ter specified by the mapping. 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 toupper
mapping by the LC_CTYPE category of the
current locale will be replaced in the
returned string by the upper-case let‐
ter specified by the mapping. 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
getline with the same string-valued
expression. If the close was success‐
ful, the function will return 0; other‐
wise, it will return non-zero.
expression|getline[var] Read a record of input from a stream
piped from the output 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
called with an expression that evalu‐
ates 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;
otherwise, 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 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 unspeci‐
fied, and all such uses of portable
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 stream
remains open, subsequent calls in which
expression evaluates to the same string
value will read subsequent records from
the file. The file will remain open
until the close function 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 concatenate) to the right of
the < (up to the end of the expression
containing the getline). The result of
evaluating such a construct is unspeci‐
fied, and all such uses of portable
applications must be put in parentheses
properly.
system(expression) Execute the command given by expression
in a manner equivalent to the sys‐
tem(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:
function name(args,...) { statements }
A function can be referred to anywhere in an nawk program; in particu‐
lar, 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 argument 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 variable. The same name must not be used
both as a variable name with global scope and as the name of a func‐
tion. 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 func‐
tion 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 arguments are supplied in a func‐
tion call than are in the function definition, the behavior is unde‐
fined.
When invoking a function, no white space can be placed between the
function name and the opening parenthesis. Function 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. Function 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 deals with bytes.
Because the concatenation operation is represented by adjacent expres‐
sions 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, 'program') for applications using
sh, because nawk programs commonly contain characters that are special
to the shell, including double-quotes. In the cases where a nawk pro‐
gram 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 characters. 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 regular expres‐
sion:
/(G|D)(2[0-9][[:alpha:]]*)/
Example 4: Print any line with a substring containing a G or D, fol‐
lowed by a sequence of digits and characters:
This example uses character classes digit and alpha to match language-
independent digit and alphabetic characters, respectively.
/(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 back‐
slash:
$2 ~ /\\/
Example 7: Write any line in which the second field contains a back‐
slash (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 num‐
ber 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/
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
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 deci‐
mal-point character of the POSIX locale) is the deci‐
mal-point character recognized in processing awk pro‐
grams (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 attributes:
/usr/bin/nawk
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWcsu │
└─────────────────────────────┴─────────────────────────────┘
/usr/xpg4/bin/awk
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Availability │SUNWxcu4 │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOawk(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 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 DESCRIP‐
TION), 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 concatenate the null string ("") to it.
SunOS 5.10 17 Jun 2005 nawk(1)
