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NAMEawk — pattern-directed scanning and processing language SYNOPSISawk
[-F
fs]
[-v
var=value
]
[program
|
-f
progfile ...]
[file ...] DESCRIPTIONawk
scans each input
file
for lines that match any of a set of patterns specified literally in
program
or in one or more files specified as
-f
progfile.
With each pattern there can be an associated action
that is to be performed when a line in a
file
matches the pattern.
Each line is matched against the pattern portion
of every pattern-action statement,
and the associated action is performed for each matched pattern.
The file name
-
means the standard input.
Any
file
of the form
var=value
is treated as an assignment, not a filename.
An assignment is evaluated
at the time it would have been opened if it were a filename,
unless the
-v
option is used. An input line is made up of fields separated by white space,
or by regular expression
FS.
The fields are denoted
$1,
$2,
...;
$0
refers to the entire line. Optionsawk
recognizes the following options and arguments:
- -F fs
Specify regular expression used to separate fields.
The default is to recognize space and tab characters,
and to discard leading spaces and tabs.
If the
-F
option is used, leading input field separators are no longer discarded. - -f progfile
Specify an awk program file.
Up to 100 program files can be specified.
The pattern-action statements in these files are executed
in the same order as the files were specified. - -v var=value
Cause
var=value
assignment to occur before the
BEGIN
action (if it exists) is executed.
StatementsA pattern-action statement has the form:
A missing
{ action }
means print the line; a missing pattern always matches.
Pattern-action statements are separated by new-lines or semicolons. An action is a sequence of statements.
A statement can be one of the following:
if(expression) statement [ else statement ]
while(expression) statement
for(expression;expression;expression) statement
for(var in array) statement
do statement while(expression)
break
continue
{[statement ...]}
expression # commonly var = expression
print [expression-list] [ > expression]
printf format [, expression-list] [ > expression]
return [expression]
next # skip remaining patterns on this input line.
delete array [expression] # delete an array element.
exit [expression] # exit immediately; status is expression. Statements are terminated by semicolons, newlines or right braces.
An empty
expression-list
stands for
$0.
String constants are quoted
(""),
with the usual C escapes recognized within.
Expressions take on string or numeric values as appropriate,
and are built using the operators
+,
-,
*,
/,
%,
^
(exponentiation), and concatenation (indicated by a blank).
The operators
++,
--,
+=,
-=,
*=,
/=,
%=,
^=,
**=,
>,
>=,
<,
<=,
==,
!=,
and
?:
are also available in expressions.
Variables can be scalars, array elements (denoted
x[i]
) or fields.
Variables are initialized to the null string.
Array subscripts can be any string, not necessarily numeric
(this allows for a form of associative memory).
Multiple subscripts such as
[i,
j,k]
are permitted.
The constituents are concatenated, separated by the value of
SUBSEP. The
print
statement prints its arguments on the standard output
(or on a file if
>file
or
>>file
is present or on a pipe if
|cmd
is present), separated by the current output field separator,
and terminated by the output record separator.
file
and
cmd
can be literal names or parenthesized expressions.
Identical string values in different statements denote the same open file.
The
printf
statement formats its expression list according to the format (see
printf(3)). Built-In FunctionsThe built-in function
close(expr)
closes the file or pipe
expr
opened by a
print
or
printf
statement or a call to
getline
with the same string-valued
expr.
This function returns zero if successful, otherwise, it returns non-zero. The customary functions
exp,
log,
sqrt,
sin,
cos,
atan2
are built in.
Other built-in functions are:
- blength[([s])]
Length of its associated argument (in bytes) taken as a string, or of
$0
if no argument. - length[([s])]
Length of its associated argument (in characters) taken as a string, or of
$0
if no argument. - rand()
Returns a random number between zero and one. - srand([expr])
Sets the seed value for
rand,
and returns the previous seed value.
If no argument is given, the time of day is used as the seed value;
otherwise,
expr
is used. - int(x)
Truncates to an integer value - substr(s, m [, n])
Return the at most
n-character
substring of
s
that begins at position
m,
numbering from 1.
If
n
is omitted, the substring is limited by the length of string
s. - 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. - match(s, ere)
Return the position, in characters, numbering from 1, in string
s
where the extended regular expression
ere
occurs, or 0 if it does not.
The variables
RSTART
and
RLENGTH
are set to the position and length of the matched string. - split(s, a[, fs])
Splits the string
s
into array elements
a[1]
,
a[2]
,
...,
a[n]
, and returns
n.
The separation is done with the regular expression
fs,
or with the field separator
FS
if
fs
is not given. - sub(ere, repl [, in])
Substitutes
repl
for the first occurrence of the extended regular expression
ere
in the string
in.
If
in
is not given,
$0
is used. - gsub
Same as
sub
except that all occurrences of the regular expression are replaced;
sub
and
gsub
return the number of replacements. - sprintf(fmt, expr, ...)
String resulting from formatting
expr ...
according to the
printf(3S)
format
fmt - system(cmd)
Executes
cmd
and returns its exit status - toupper(s)
Converts the argument string
s
to uppercase and returns the result. - tolower(s)
Converts the argument string
s
to lowercase and returns the result.
The built-in function
getline
sets
$0
to the next input record from the current input file;
getline < file
sets
$0
to the next record from
file.
getline
x
sets variable
x
instead.
Finally,
cmd | getline
pipes the output of
cmd
into
getline;
each call of
getline
returns the next line of output from
cmd.
In all cases,
getline
returns 1 for a successful input,
0 for end of file, and -1 for an error. PatternsPatterns are arbitrary Boolean combinations
(with
! || &&)
of regular expressions and relational expressions.
awk
supports Extended Regular Expressions as described in
regexp(5).
Isolated regular expressions in a pattern apply to the entire line.
Regular expressions can also occur in
relational expressions, using the operators
~
and
!~.
/re/
is a constant regular expression;
any string (constant or variable) can be used as a regular expression,
except in the position of an isolated regular expression in a pattern. A pattern can consist of two patterns separated by a comma;
in this case, the action is performed for all lines
from an occurrence of the first pattern
though an occurrence of the second. A relational expression is one of the following:
expression matchop regular-expression expression relop expression (expr,expr,...) in array-name
where a relop is any of the six relational operators in C,
and a matchop is either
~
(matches) or
!~
(does not match).
A conditional is an arithmetic expression,
a relational expression, or a Boolean combination of the two. The special patterns
BEGIN
and
END
can be used to capture control before the first input line is read
and after the last.
BEGIN
and
END
do not combine with other patterns. Special CharactersThe following special escape sequences are recognized by
awk
in both regular expressions and strings:
- Escape
Meaning - \a
alert character - \b
backspace character - \f
form-feed character - \n
new-line character - \r
carriage-return character - \t
tab character - \v
vertical-tab character - \nnn
1- to 3-digit octal value
nnn - \xhhh
1- to n-digit hexadecimal number
Variable NamesVariable names with special meanings are:
- FS
Input field separator regular expression; a space character by default;
also settable by option
-Ffs. - NF
The number of fields in the current record. - 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. - 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. - FILENAME
A pathname of the current input file. - RS
The input record separator; a newline character by default. - OFS
The
print
statement output field separator; a space character by default. - ORS
The
print
statement output record separator; a newline character by default. - OFMT
Output format for numbers (default
%.6g).
If the value of
OFMT
is not a floating-point format specification, the results are unspecified. - CONVFMT
Internal conversion format for numbers (default
%.6g).
If the value of
CONVFMT
is not a floating-point format specification, the results are unspecified. - SUBSEP
The subscript separator string for multi-dimensional arrays; the default
value is "\034" - 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,
awk
will treat the next non-null element of
ARGV,
up to the current value of
ARGC-1,
inclusive, as the name of the next input file. Thus, setting an element of
ARGV
to null means that it will not be treated as an input file. The name
-
indicates
the standard input. If an argument matches the format of an
assignment
operand, this argument will be treated as an assignment rather than a
file
argument. - ENVIRON
Array of environment variables; subscripts are names.
For example, if environment variable
V=thing,
ENVIRON["V"]
produces
thing. - 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. - RLENGTH
The length of the string matched by the
match
function.
Functions can be defined (at the position of a pattern-action statement)
as follows:
function foo(a, b, c) { ...; return x } Parameters are passed by value if scalar, and by reference if array name.
Functions can be called recursively.
Parameters are local to the function; all other variables are global. Note that if pattern-action statements are used in an HP-UX
command line as an argument to the
awk
command, the pattern-action statement
must be enclosed in single quotes to protect it from the shell.
For example, to print lines longer than 72 characters,
the pattern-action statement as used in a script
(-f
progfile
command form) is:
The same pattern action statement used as an argument to the
awk
command is quoted in this manner:
EXTERNAL INFLUENCESEnvironment Variables- LANG
Provides a default value for the internationalization variables that are unset
or null.
If
LANG
is unset or null, the default value of "C" (see
lang(5))
is used.
If any of the internationalization variables contains an invalid setting,
awk
will behave as if all internationalization variables are set to "C".
See
environ(5). - LC_ALL
If set to a non-empty string value, overrides the values of all the other
internationalization variables. - LC_CTYPE
Determines the interpretation of text as single and/or
multi-byte characters, the classification of characters as printable,
and the characters matched by character class expressions in regular
expressions. - LC_NUMERIC
Determines the radix character used when interpreting numeric input, performing
conversion 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). - LC_COLLATE
Determines the locale for the behavior of ranges, equivalence classes
and multi-character collating elements within regular expressions. - LC_MESSAGES
Determines the locale that should be used to affect the format and contents
of diagnostic messages written to standard error and informative messages
written to standard output. - NLSPATH
Determines the location of message catalogues for the processing of
LC_MESSAGES. - PATH
Determines the search path when looking for commands executed by
system(cmd),
or input and output pipes.
In addition, all environment variables will be visible via the
awk
variable
ENVIRON. International Code Set SupportSingle- and multi-byte character code sets are supported
except that variable names must contain only ASCII
characters and regular expressions
must contain only valid characters. DIAGNOSTICSawk
supports up to 199 fields
($1,
$2,
...,
$199)
per record. EXAMPLESPrint lines longer than 72 characters:
Print first two fields in opposite order:
Same, with input fields separated by comma and/or blanks and tabs:
BEGIN { FS = ",[ \t]*|[ \t]+" }
{ print $2, $1 } Add up first column, print sum and average:
{ s += $1 }"
END { print "sum is", s, " average is", s/NR } Print all lines between start/stop pairs:
Simulate
echo
command (see
echo(1)):
BEGIN { # Simulate echo(1)
for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
printf "\n"
exit } AUTHORawk
was developed by AT&T, IBM, OSF, and HP. SEE ALSOlex(1),
sed(1). A. V. Aho, B. W. Kernighan, P. J. Weinberger:
The AWK Programming Language,
Addison-Wesley, 1988. STANDARDS CONFORMANCEawk: SVID2, SVID3, XPG2, XPG3, XPG4, POSIX.2 |
