MAWK(1) USER COMMANDS MAWK(1)
NAME
mawk - pattern scanning and text processing language
SYNOPSIS
mawk [-W option] [-F value] [-v var=value] [--] 'program text' [file ...]
mawk [-W option] [-F value] [-v var=value] [-f program-file] [--] [file ...]
DESCRIPTION
mawk is an interpreter for the AWK Programming Language. The AWK language is useful for manipulation of data files, text retrieval and
processing, and for prototyping and experimenting with algorithms. mawk is a new awk meaning it implements the AWK language as defined in
Aho, Kernighan and Weinberger, The AWK Programming Language, Addison-Wesley Publishing, 1988. (Hereafter referred to as the AWK book.)
mawk conforms to the Posix 1003.2 (draft 11.3) definition of the AWK language which contains a few features not described in the AWK book,
and mawk provides a small number of extensions.
An AWK program is a sequence of pattern {action} pairs and function definitions. Short programs are entered on the command line usually
enclosed in ' ' to avoid shell interpretation. Longer programs can be read in from a file with the -f option. Data input is read from
the list of files on the command line or from standard input when the list is empty. The input is broken into records as determined by the
record separator variable, RS. Initially, RS = "
" and records are synonymous with lines. Each record is compared against each pattern
and if it matches, the program text for {action} is executed.
OPTIONS
-F value sets the field separator, FS, to value.
-f file Program text is read from file instead of from the command line. Multiple -f options are allowed.
-v var=value assigns value to program variable var.
-- indicates the unambiguous end of options.
The above options will be available with any Posix compatible implementation of AWK, and implementation specific options are prefaced with
-W. mawk provides six:
-W version mawk writes its version and copyright to stdout and compiled limits to stderr and exits 0.
-W dump writes an assembler like listing of the internal representation of the program to stdout and exits 0 (on successful compila-
tion).
-W interactive sets unbuffered writes to stdout and line buffered reads from stdin. Records from stdin are lines regardless of the value
of RS.
-W exec file Program text is read from file and this is the last option. Useful on systems that support the #! "magic number" convention
for executable scripts.
-W sprintf=num adjusts the size of mawk's internal sprintf buffer to num bytes. More than rare use of this option indicates mawk should be
recompiled.
-W posix_space forces mawk not to consider '
' to be space.
The short forms -W[vdiesp] are recognized and on some systems -We is mandatory to avoid command line length limitations.
THE AWK LANGUAGE
1. Program structure
An AWK program is a sequence of pattern {action} pairs and user function definitions.
A pattern can be:
BEGIN
END
expression
expression , expression
One, but not both, of pattern {action} can be omitted. If {action} is omitted it is implicitly { print }. If pattern is omitted, then it
is implicitly matched. BEGIN and END patterns require an action.
Statements are terminated by newlines, semi-colons or both. Groups of statements such as actions or loop bodies are blocked via { ... } as
in C. The last statement in a block doesn't need a terminator. Blank lines have no meaning; an empty statement is terminated with a semi-
colon. Long statements can be continued with a backslash, . A statement can be broken without a backslash after a comma, left brace, &&,
||, do, else, the right parenthesis of an if, while or for statement, and the right parenthesis of a function definition. A comment starts
with # and extends to, but does not include the end of line.
The following statements control program flow inside blocks.
if ( expr ) statement
if ( expr ) statement else statement
while ( expr ) statement
do statement while ( expr )
for ( opt_expr ; opt_expr ; opt_expr ) statement
for ( var in array ) statement
continue
break
2. Data types, conversion and comparison
There are two basic data types, numeric and string. Numeric constants can be integer like -2, decimal like 1.08, or in scientific notation
like -1.1e4 or .28E-3. All numbers are represented internally and all computations are done in floating point arithmetic. So for example,
the expression 0.2e2 == 20 is true and true is represented as 1.0.
String constants are enclosed in double quotes.
"This is a string with a newline at the end.
"
Strings can be continued across a line by escaping () the newline. The following escape sequences are recognized.
\
" "
a alert, ascii 7
backspace, ascii 8
tab, ascii 9
newline, ascii 10
v vertical tab, ascii 11
f formfeed, ascii 12
carriage return, ascii 13
ddd 1, 2 or 3 octal digits for ascii ddd
xhh 1 or 2 hex digits for ascii hh
If you escape any other character c, you get c, i.e., mawk ignores the escape.
There are really three basic data types; the third is number and string which has both a numeric value and a string value at the same time.
User defined variables come into existence when first referenced and are initialized to null, a number and string value which has numeric
value 0 and string value "". Non-trivial number and string typed data come from input and are typically stored in fields. (See section
4).
The type of an expression is determined by its context and automatic type conversion occurs if needed. For example, to evaluate the state-
ments
y = x + 2 ; z = x "hello"
The value stored in variable y will be typed numeric. If x is not numeric, the value read from x is converted to numeric before it is
added to 2 and stored in y. The value stored in variable z will be typed string, and the value of x will be converted to string if neces-
sary and concatenated with "hello". (Of course, the value and type stored in x is not changed by any conversions.) A string expression is
converted to numeric using its longest numeric prefix as with atof(3). A numeric expression is converted to string by replacing expr with
sprintf(CONVFMT, expr), unless expr can be represented on the host machine as an exact integer then it is converted to sprintf("%d", expr).
Sprintf() is an AWK built-in that duplicates the functionality of sprintf(3), and CONVFMT is a built-in variable used for internal conver-
sion from number to string and initialized to "%.6g". Explicit type conversions can be forced, expr "" is string and expr+0 is numeric.
To evaluate, expr1 rel-op expr2, if both operands are numeric or number and string then the comparison is numeric; if both operands are
string the comparison is string; if one operand is string, the non-string operand is converted and the comparison is string. The result is
numeric, 1 or 0.
In boolean contexts such as, if ( expr ) statement, a string expression evaluates true if and only if it is not the empty string "";
numeric values if and only if not numerically zero.
3. Regular expressions
In the AWK language, records, fields and strings are often tested for matching a regular expression. Regular expressions are enclosed in
slashes, and
expr ~ /r/
is an AWK expression that evaluates to 1 if expr "matches" r, which means a substring of expr is in the set of strings defined by r. With
no match the expression evaluates to 0; replacing ~ with the "not match" operator, !~ , reverses the meaning. As pattern-action pairs,
/r/ { action } and $0 ~ /r/ { action }
are the same, and for each input record that matches r, action is executed. In fact, /r/ is an AWK expression that is equivalent to ($0 ~
/r/) anywhere except when on the right side of a match operator or passed as an argument to a built-in function that expects a regular
expression argument.
AWK uses extended regular expressions as with egrep(1). The regular expression metacharacters, i.e., those with special meaning in regular
expressions are
^ $ . [ ] | ( ) * + ?
Regular expressions are built up from characters as follows:
c matches any non-metacharacter c.
c matches a character defined by the same escape sequences used in string constants or the literal character c if c is
not an escape sequence.
. matches any character (including newline).
^ matches the front of a string.
$ matches the back of a string.
[c1c2c3...] matches any character in the class c1c2c3... . An interval of characters is denoted c1-c2 inside a class [...].
[^c1c2c3...] matches any character not in the class c1c2c3...
Regular expressions are built up from other regular expressions as follows:
r1r2 matches r1 followed immediately by r2 (concatenation).
r1 | r2 matches r1 or r2 (alternation).
r* matches r repeated zero or more times.
r+ matches r repeated one or more times.
r? matches r zero or once.
(r) matches r, providing grouping.
The increasing precedence of operators is alternation, concatenation and unary (*, + or ?).
For example,
/^[_a-zA-Z][_a-zA-Z0-9]*$/ and
/^[-+]?([0-9]+.?|.[0-9])[0-9]*([eE][-+]?[0-9]+)?$/
are matched by AWK identifiers and AWK numeric constants respectively. Note that . has to be escaped to be recognized as a decimal point,
and that metacharacters are not special inside character classes.
Any expression can be used on the right hand side of the ~ or !~ operators or passed to a built-in that expects a regular expression. If
needed, it is converted to string, and then interpreted as a regular expression. For example,
BEGIN { identifier = "[_a-zA-Z][_a-zA-Z0-9]*" }
$0 ~ "^" identifier
prints all lines that start with an AWK identifier.
mawk recognizes the empty regular expression, //, which matches the empty string and hence is matched by any string at the front, back and
between every character. For example,
echo abc | mawk { gsub(//, "X") ; print }
XaXbXcX
4. Records and fields
Records are read in one at a time, and stored in the field variable $0. The record is split into fields which are stored in $1, $2, ...,
$NF. The built-in variable NF is set to the number of fields, and NR and FNR are incremented by 1. Fields above $NF are set to "".
Assignment to $0 causes the fields and NF to be recomputed. Assignment to NF or to a field causes $0 to be reconstructed by concatenating
the $i's separated by OFS. Assignment to a field with index greater than NF, increases NF and causes $0 to be reconstructed.
Data input stored in fields is string, unless the entire field has numeric form and then the type is number and string. For example,
echo 24 24E |
mawk '{ print($1>100, $1>"100", $2>100, $2>"100") }'
0 1 1 1
$0 and $2 are string and $1 is number and string. The first comparison is numeric, the second is string, the third is string (100 is con-
verted to "100"), and the last is string.
5. Expressions and operators
The expression syntax is similar to C. Primary expressions are numeric constants, string constants, variables, fields, arrays and function
calls. The identifier for a variable, array or function can be a sequence of letters, digits and underscores, that does not start with a
digit. Variables are not declared; they exist when first referenced and are initialized to null.
New expressions are composed with the following operators in order of increasing precedence.
assignment = += -= *= /= %= ^=
conditional ? :
logical or ||
logical and &&
array membership in
matching ~ !~
relational < > <= >= == !=
concatenation (no explicit operator)
add ops + -
mul ops * / %
unary + -
logical not !
exponentiation ^
inc and dec ++ -- (both post and pre)
field $
Assignment, conditional and exponentiation associate right to left; the other operators associate left to right. Any expression can be
parenthesized.
6. Arrays
Awk provides one-dimensional arrays. Array elements are expressed as array[expr]. Expr is internally converted to string type, so, for
example, A[1] and A["1"] are the same element and the actual index is "1". Arrays indexed by strings are called associative arrays. Ini-
tially an array is empty; elements exist when first accessed. An expression, expr in array evaluates to 1 if array[expr] exists, else to
0.
There is a form of the for statement that loops over each index of an array.
for ( var in array ) statement
sets var to each index of array and executes statement. The order that var transverses the indices of array is not defined.
The statement, delete array[expr], causes array[expr] not to exist. mawk supports an extension, delete array, which deletes all elements
of array.
Multidimensional arrays are synthesized with concatenation using the built-in variable SUBSEP. array[expr1,expr2] is equivalent to
array[expr1 SUBSEP expr2]. Testing for a multidimensional element uses a parenthesized index, such as
if ( (i, j) in A ) print A[i, j]
7. Builtin-variables
The following variables are built-in and initialized before program execution.
ARGC number of command line arguments.
ARGV array of command line arguments, 0..ARGC-1.
CONVFMT format for internal conversion of numbers to string, initially = "%.6g".
ENVIRON array indexed by environment variables. An environment string, var=value is stored as ENVIRON[var] = value.
FILENAME name of the current input file.
FNR current record number in FILENAME.
FS splits records into fields as a regular expression.
NF number of fields in the current record.
NR current record number in the total input stream.
OFMT format for printing numbers; initially = "%.6g".
OFS inserted between fields on output, initially = " ".
ORS terminates each record on output, initially = "
".
RLENGTH length set by the last call to the built-in function, match().
RS input record separator, initially = "
".
RSTART index set by the last call to match().
SUBSEP used to build multiple array subscripts, initially = "