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Návod, kniha: POSIX Programmer's Manual
awk [-F ERE]
-f progfile ...
[-v
assignment]
...[ argument
...]
Either the pattern or the action (including the enclosing brace characters) can
be omitted.
A missing pattern shall match any record of input, and a missing action shall be
equivalent to:
Execution of the awk program shall start 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) shall be processed in turn by reading data from the file until a
record separator is seen ( <newline> by default). Before the first
reference to a field in the record is evaluated, the record shall be split
into fields, according to the rules in Regular Expressions , using the value
of FS that was current at the time the record was read. Each pattern in
the program then shall be evaluated in the order of occurrence, and the action
associated with each pattern that matches the current record executed. The
action for a matching pattern shall be executed before evaluating subsequent
patterns. Finally, the actions associated with all END patterns shall
be executed in the order they occur in the program.
Table: Expressions in Decreasing Precedence in awk
Each expression shall have either a string value, a numeric value, or both.
Except as stated for specific contexts, the value of an expression shall be
implicitly converted to the type needed for the context in which it is used. A
string value shall be converted to a numeric value by the equivalent of the
following calls to functions defined by the ISO C standard:
A numeric value that is exactly equal to the value of an integer (see
Concepts Derived from the ISO C Standard ) shall be converted to
a string by the equivalent of a call to the sprintf function (see
String Functions ) 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 shall be 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. The result of the
conversion is unspecified if the value of CONVFMT is not a
floating-point format specification. This volume of
IEEE Std 1003.1-2001 specifies no explicit conversions between
numbers and strings. An application can force an expression to be treated as a
number by adding zero to it, or can force it to be treated as a string by
concatenating the null string ( "" ) to it.
A string value shall be considered a numeric string if it comes from one
of the following:
shall be equivalent to the value returned by the ISO C standard function
call:
The expression:
shall be equivalent to the ISO C standard expression:
except that lvalue shall be evaluated only once. The value of the expression:
shall be equivalent to the value returned by the ISO C standard function
call:
The expression:
shall be equivalent to the ISO C standard expression:
except that lvalue shall be evaluated only once.
Variables and fields shall be set by the assignment statement:
and the type of expression shall determine the resulting variable type.
The assignment includes the arithmetic assignments ( "+=" ,
"-=" , "*=" , "/=" ,
"%=" , "^=" , "++" ,
"--" ) all of which shall produce a numeric result. The
left-hand side of an assignment and the target of increment and decrement
operators can be one of a variable, an array with index, or a field selector.
The awk language supplies arrays that are used for storing numbers or
strings. Arrays need not be declared. They shall initially be empty, and their
sizes shall change 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
thus as an expression, as described in the grammar; see Grammar .
Unsubscripted array names can be used in only the following contexts:
The application shall ensure that a multi-dimensioned index used with the
in operator is parenthesized. The in operator, which tests for
the existence of a particular array element, shall not cause that element to
exist. Any other reference to a nonexistent array element shall automatically
create it.
Comparisons (with the '<' , "<=" ,
"!=" , "==" , '>' , and
">=" operators) shall be made numerically if both operands
are numeric, if one is numeric and the other has a string value that is a
numeric string, or if one is numeric and the other has the uninitialized
value. Otherwise, operands shall be converted to strings as required and a
string comparison shall be made using the locale-specific collation sequence.
The value of the comparison expression shall be 1 if the relation is true, or
0 if the relation is false.
Table: Escape Sequences in awk
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 shall 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 shall
evaluate to a value of 1, and the "!~" expression shall
evaluate to a value of 0. (The regular expression matching operation is as
defined by the term matched in the Base Definitions volume of
IEEE Std 1003.1-2001, Section 9.1, Regular Expression
Definitions, where a match occurs on any part of the string unless the regular
expression is limited with the circumflex or dollar sign special characters.)
If the regular expression does not match the string, the '~' expression
shall evaluate to a value of 0, and the "!~" expression shall
evaluate to a value of 1. If the right-hand operand is any expression other
than the lexical token ERE, the string value of the expression shall be
interpreted as an extended regular expression, including the escape
conventions described above. Note that these same escape conventions shall
also be applied in determining the value of a string literal (the lexical
token STRING), and thus shall be 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 shall be the equivalent of:
The ere argument to the gsub, match, sub functions,
and the fs argument to the split function (see String Functions
) shall be interpreted as extended regular expressions. These can be either
ERE tokens or arbitrary expressions, and shall be 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 shall be a single <space>. The following describes FS
behavior:
which shall iterate, assigning each index of array to
variable in an unspecified order. The results of adding new elements to
array within such a for loop are undefined. If a break or
continue statement occurs outside of a loop, the behavior is undefined.
The delete statement shall remove an individual array element. Thus, the
following code deletes an entire array:
The next statement shall cause 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 shall invoke 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
shall terminate the program without further execution of END actions.
If an expression is specified in an exit statement, its numeric value
shall be the exit status of awk, unless subsequent errors are
encountered or a subsequent exit statement with an expression is
executed.
In all cases, the expression shall be evaluated to produce a string that
is used as a pathname into which to write (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 shall be opened, creating it if necessary and using the first form,
truncating the file. The output then shall be appended to the file. As long as
the file remains open, subsequent calls in which expression evaluates
to the same string value shall simply append output to the file. The file
remains open until the close function (see Input/Output and General
Functions ) is called with an expression that evaluates to the same string
value.
The third form shall write output onto a stream piped to the input of a command.
The stream shall be created if no stream is currently open with the value of
expression as its command name. The stream created shall be equivalent
to one created by a call to the popen() function defined in the System
Interfaces volume of IEEE Std 1003.1-2001 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 shall write
output to the existing stream. The stream shall remain open until the
close function (see Input/Output and General Functions ) is called with
an expression that evaluates to the same string value. At that time, the
stream shall be closed as if by a call to the pclose() function defined
in the System Interfaces volume of IEEE Std 1003.1-2001.
As described in detail by the grammar in Grammar , these output statements shall
take a comma-separated list of expressions referred to 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 shall write 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 shall be
taken as strings, being converted if necessary; this conversion shall be as
described in Expressions in awk , with the exception that the printf
format in OFMT shall be used instead of the value in CONVFMT. An
empty expression list shall stand for the whole input record ($0).
The printf statement shall produce output based on a notation similar to
the File Format Notation used to describe file formats in this volume of
IEEE Std 1003.1-2001 (see the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 5, File Format Notation). Output
shall be 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:
awk: skenování a zpracování jazyka
Originální popis anglicky: awk - pattern scanning and processing languageNávod, kniha: POSIX Programmer's Manual
STRUČNĚ
awk [-F ERE][-v assignment] ... program [argument ...]POPIS / INSTRUKCE
The awk utility shall execute programs written in the awk programming language, which is specialized for textual data manipulation. An awk program is a sequence of patterns and corresponding actions. When input is read that matches a pattern, the action associated with that pattern is carried out. Input shall be interpreted as a sequence of records. By default, a record is a line, less its terminating <newline>, but this can be changed by using the RS built-in variable. Each record of input shall be matched in turn against each pattern in the program. For each pattern matched, the associated action shall be executed. The awk utility shall interpret each input record as a sequence of fields where, by default, a field is a string of non- <blank>s. This default white-space field delimiter can be changed by using the FS built-in variable or -F ERE. The awk utility shall denote the first field in a record $1, the second $2, and so on. The symbol $0 shall refer to the entire record; setting any other field causes the re-evaluation of $0. Assigning to $0 shall reset the values of all other fields and the NF built-in variable.OPTIONS
The awk utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. The following options shall be supported:- -F ERE
- Define the input field separator to be the extended regular expression ERE, before any input is read; see Regular Expressions .
- -f progfile
- Specify the pathname of the file progfile containing an awk program. If multiple instances of this option are specified, the concatenation of the files specified as progfile in the order specified shall be the awk program. The awk program can alternatively be specified in the command line as a single argument.
- -v assignment
- The application shall ensure that the assignment
argument is in the same form as an assignment operand. The
specified variable assignment shall occur prior to executing the
awk program, including the actions associated with BEGIN
patterns (if any). Multiple occurrences of this option can be specified.
OPERANDS
The following operands shall be supported:- program
- If no -f option is specified, the first operand to awk shall be the text of the awk program. The application shall supply the program operand as a single argument to awk. If the text does not end in a <newline>, awk shall interpret 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 shall be used.
- assignment
An operand that begins with an underscore or
alphabetic character from the portable character set (see the table in the
Base Definitions volume of IEEE Std 1003.1-2001, Section 6.1,
Portable Character Set), followed by a sequence of underscores, digits, and
alphabetics from the portable character set, followed by the '='
character, shall specify a variable assignment rather than a pathname. The
characters before the '=' represent the name of an awk variable;
if that name is an awk reserved word (see Grammar ) the behavior is
undefined. The characters following the equal sign shall be interpreted as if
they appeared in the awk program preceded and followed by a
double-quote ( ' )' character, as a STRING token (see Grammar ),
except that if the last character is an unescaped backslash, it shall be
interpreted as a literal backslash rather than as the first character of the
sequence "\"" . The variable shall be assigned the value
of that STRING token and, if appropriate, shall be considered a
numeric string (see Expressions in awk ), the variable shall also be
assigned its numeric value. Each such variable assignment shall occur just
prior to the processing of the following file, if any. Thus, an
assignment before the first file argument shall be executed after the
BEGIN actions (if any), while an assignment after the last file
argument shall occur before the END actions (if any). If there are no
file arguments, assignments shall be executed before processing the
standard input.
STDIN
The standard input shall be used only if no file operands are specified, or if a file operand is '-' ; see the INPUT FILES section. If the awk program contains no actions and no patterns, but is otherwise a valid awk program, standard input and any file operands shall not be read and awk shall exit with a return status of zero.INPUT FILES
Input files to the awk program from any of the following sources shall be text files:- *
- Any file operands or their equivalents, achieved by modifying the awk variables ARGV and ARGC
- *
- Standard input in the absence of any file operands
- *
- Arguments to the getline function
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of awk:- LANG
- Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- LC_ALL
- If set to a non-empty string value, override the values of all the other internationalization variables.
- LC_COLLATE
- Determine the locale for the behavior of ranges, equivalence classes, and multi-character collating elements within regular expressions and in comparisons of string values.
- LC_CTYPE
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files), the behavior of character classes within regular expressions, the identification of characters as letters, and the mapping of uppercase and lowercase characters for the toupper and tolower functions.
- LC_MESSAGES
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- LC_NUMERIC
- Determine the radix character used when interpreting numeric input, performing conversions between numeric and string values, and formatting numeric output. Regardless of locale, the period character (the decimal-point character of the POSIX locale) is the decimal-point character recognized in processing awk programs (including assignments in command line arguments).
- NLSPATH
- Determine the location of message catalogs for the processing of LC_MESSAGES .
- PATH
- Determine the search path when looking for commands
executed by system(expr), or input and output pipes; see the
Base Definitions volume of IEEE Std 1003.1-2001, Chapter 8,
Environment Variables.
ASYNCHRONOUS EVENTS
Default.STDOUT
The nature of the output files depends on the awk program.STDERR
The standard error shall be used only for diagnostic messages.OUTPUT FILES
The nature of the output files depends on the awk program.EXTENDED DESCRIPTION
Overall Program Structure
An awk program is composed of pairs of the form:
pattern { action }
{ print }
Expressions in awk
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 operators shall be 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). The precise syntax of expressions is given in Grammar .| 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 array | Multi-dimension array | Numeric | Left |
| membership | |||
| expr && expr | Logical AND | Numeric | Left |
| expr || expr | Logical OR | Numeric | Left |
| expr1 ? expr2 : expr3 | Conditional expression | Type of selected | Right |
| expr2 or expr3 | |||
| lvalue ^= expr | Exponentiation assignment | Numeric | Right |
| lvalue %= expr | Modulus assignment | Numeric | Right |
| lvalue *= expr | Multiplication assignment | Numeric | Right |
| 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 |
setlocale(LC_NUMERIC, ""); numeric_value = atof(string_value);
- 1.
- Field variables
- 2.
- Input from the getline() function
- 3.
- FILENAME
- 4.
- ARGV array elements
- 5.
- ENVIRON array elements
- 6.
- Array elements created by the split() function
- 7.
- A command line variable assignment
- 8.
- Variable assignment from another numeric string variable
- *
- All leading and trailing <blank>s are discarded.
- *
- If the first non- <blank> is '+' or '-' , it is discarded.
- *
- Changing each occurrence of the decimal point character from the current locale to a period.
- *
- 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)
expr1 ^ expr2
pow(expr1, expr2)
lvalue ^= expr
lvalue = pow(lvalue, expr)
expr1 % expr2
fmod(expr1, expr2)
lvalue %= expr
lvalue = fmod(lvalue, expr)
lvalue = expression
- *
- A parameter in a function definition or function call
- *
- The NAME token following any use of the keyword in as specified in the grammar (see Grammar ); if the name used in this context is not an array name, the behavior is undefined
var[expr1, expr2, ... exprn]var[expr1 SUBSEP expr2 SUBSEP ... SUBSEP exprn]
Variables and Special Variables
Variables can be used in an awk program by referencing them. With the exception of function parameters (see User-Defined Functions ), they are not explicitly declared. Function parameter names shall be local to the function; all other variable names shall be global. The same name shall not be used as both a function parameter name and as the name of a function or a special awk variable. The same name shall not be used both as a variable name with global scope and as the name of a function. The same name shall not be used within the same scope both as a scalar variable and as an array. Uninitialized variables, including scalar variables, array elements, and field variables, shall have an uninitialized value. An uninitialized value shall have both a numeric value of zero and a string value of the empty string. Evaluation of variables with an uninitialized value, to either string or numeric, shall be determined by the context in which they are used. Field variables shall be 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 context. New field variables can be created by assigning a value to them. References to nonexistent fields (that is, fields after $ NF), shall evaluate to the uninitialized value. Such references shall not create new fields. However, assigning to a nonexistent field (for example, $( NF+2)=5) shall increase the value of NF; create any intervening fields with the uninitialized value; and cause the value of $0 to be recomputed, with the fields being separated by the value of OFS. Each field variable shall have a string value or an uninitialized value when created. Field variables shall have the uninitialized value when created from $0 using FS and the variable does not contain any characters. If appropriate, the field variable shall be considered a numeric string (see Expressions in awk ). Implementations shall support the following other special variables that are set by 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.
- CONVFMT
- The printf format for converting numbers to strings (except for output statements, where OFMT is used); "%.6g" by default.
- ENVIRON
- An array representing the value of the environment, as described in the exec functions defined in the System Interfaces volume of IEEE Std 1003.1-2001. The indices of the array shall be strings consisting of the names of the environment variables, and the value of each array element shall be a string consisting of the value of that variable. If appropriate, the environment variable shall be considered a numeric string (see Expressions in awk ); the array element shall also have its numeric value.
- FILENAME
- A pathname of the current input file. Inside a BEGIN action the value is undefined. Inside an END action the value shall be 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 shall be zero. Inside an END action the value shall be the number of the last record processed in the last file processed.
- FS
- Input field separator regular expression; a <space> 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 shall retain 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 shall be zero. Inside an END action the value shall be the number of the last record processed.
- OFMT
- The printf format for converting numbers to strings in output statements (see 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 separation; <space> by default.
- ORS
- The print statement output record separator; a <newline> by default.
- RLENGTH
- The length of the string matched by the match function.
- RS
- The first character of the string value of RS shall be the input record separator; a <newline> by default. If RS contains more than one character, the results are unspecified. If RS is null, then records are separated by sequences consisting of a <newline> plus one or more blank lines, leading or trailing blank lines shall not result in empty records at the beginning or end of the input, and a <newline> shall always be a field separator, no matter what the value of FS is.
- RSTART
- The starting position of the string matched by the match function, numbering from 1. This shall always be equivalent to the return value of the match function.
- SUBSEP
- The subscript separator string for multi-dimensional
arrays; the default value is implementation-defined.
Regular Expressions
The awk utility shall make use of the extended regular expression notation (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 9.4, Extended Regular Expressions) except that it shall allow the use of C-language conventions for escaping special characters within the EREs, as specified in the table in the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 5, File Format Notation ( '\\' , '\a' , '\b' , '\f' , '\n' , '\r' , '\t' , '\v' ) and the following table; these escape sequences shall be recognized both inside and outside bracket expressions. Note that records need not be separated by <newline>s and string constants can contain <newline>s, so even the "\n" sequence is valid in awk EREs. Using a slash character within an ERE requires the escaping shown in the following table.| Escape | ||
| Sequence | Description | Meaning |
| \" | Backslash quotation-mark | Quotation-mark character |
| \/ | Backslash slash | Slash character |
| \ddd | A backslash character followed by the longest sequence of one, two, or three octal-digit characters (01234567). If all of the digits are 0 (that is, representation of the NUL character), the behavior is undefined. | The character whose encoding is represented by the one, two, or three-digit octal integer. Multi-byte characters require multiple, concatenated escape sequences of this type, including the leading '\' for each byte. |
| \c | A backslash character followed by any character not described in this table or in the table in the Base Definitions volume of IEEE Std 1003.1-2001, Chapter 5, File Format Notation ( '\\' , '\a' , '\b' , '\f' , '\n' , '\r' , '\t' , '\v' ). | Undefined |
$0 ~ /ere/
- 1.
- If FS is a null string, the behavior is unspecified.
- 2.
- If FS is a single character:
- a.
- If FS is <space>, skip leading and trailing <blank>s; fields shall be delimited by sets of one or more <blank>s.
- b.
- Otherwise, if FS is any other character c, fields shall be delimited by each single occurrence of c.
- 3.
- Otherwise, the string value of FS shall be considered to be an extended regular expression. Each occurrence of a sequence matching the extended regular expression shall delimit fields.
Patterns
A pattern is any valid expression, a range specified by two expressions separated by a comma, or one of the two special patterns BEGIN or END.Special Patterns
The awk utility shall recognize two special patterns, BEGIN and END. Each BEGIN pattern shall be matched once and its associated action executed before the first record of input is read (except possibly by use of the getline function-see Input/Output and General Functions - in a prior BEGIN action) and before command line assignment is done. Each END pattern shall be matched once and its associated action executed after the last record of input has been read. These two patterns shall have associated actions. BEGIN and END shall not combine with other patterns. Multiple BEGIN and END patterns shall be allowed. The actions associated with the BEGIN patterns shall be 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 awk program consists of only actions with the pattern BEGIN, and the BEGIN action contains no getline function, awk shall exit without reading its input when the last statement in the last BEGIN action is executed. If an awk program consists of only actions with the pattern END or only actions with the patterns BEGIN and END, the input shall be read before the statements in the END actions are executed.Expression Patterns
An expression pattern shall be evaluated as if it were an expression in a Boolean context. If the result is true, the pattern shall be considered to match, and the associated action (if any) shall be executed. If the result is false, the action shall not be executed.Pattern Ranges
A pattern range consists of two expressions separated by a comma; in this case, the action shall be 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 as shown in the grammar in Grammar . Any single statement can be replaced by a statement list enclosed in braces. The application shall ensure that statements in a statement list are separated by <newline>s or semicolons. Statements in a statement list shall be executed sequentially in the order that they appear. The expression acting as the conditional in an if statement shall be evaluated and if it is non-zero or non-null, the following statement shall be executed; otherwise, if else is present, the statement following the else shall be executed. The if, while, do... while, for, break, and continue statements are based on the ISO C standard (see Concepts Derived from the ISO C Standard ), except that the Boolean expressions shall be treated as described in Expressions in awk , and except in the case of:for (variable in array)
for (index in array)
delete array[index]
Output Statements
Both print and printf statements shall write to standard output by default. The output shall be written to the location specified by output_redirection if one is supplied, as follows:> expression>> expression| expression
- 1.
- The format shall be an actual character string rather than a graphical representation. Therefore, it cannot contain empty character positions. The <space> in the format string, in any context other than a flag of a conversion specification, shall be treated as an ordinary character that is copied to the output.
- 2.
- If the character set contains a ' ' character and that character appears in the format string, it shall be treated as an ordinary character that is copied to the output.
- 3.
- The escape sequences beginning with a backslash character shall be treated as sequences of ordinary characters that are copied to the output. Note that these same sequences shall be interpreted lexically by awk when they appear in literal strings, but they shall not be 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 shall be fetched and its numeric value taken as the field width or precision.
- 5.
- The implementation shall not precede or follow output from the d or u conversion specifier characters with <blank>s not specified by the format string.
- 6.
- The implementation shall not precede output from the o conversion specifier character with leading zeros not specified by the format string.
- 7.
- For the c conversion specifier character: if the argument has a numeric value, the character whose encoding is that value shall be 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 shall be output; if the string does not contain any characters, the behavior is undefined.
- 8.
- For each conversion specification that consumes an argument, the next expression argument shall be evaluated. With the exception of the c conversion specifier character, the value shall be converted (according to the rules specified in Expressions in awk ) 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.
Functions
The awk language has a variety of built-in functions: arithmetic, string, input/output, and general.Arithmetic Functions
The arithmetic functions, except for int, shall be based on the ISO C standard (see Concepts Derived from 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 (see 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.- atan2(y,x)
- Return arctangent of y/x in radians in the range [-pi,pi].
- 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)
- Return the argument truncated to an integer. Truncation shall be 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 shall
be returned.
String Functions
The string functions in the following list shall be supported. Although the grammar (see 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.- <