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MAWK(1) USER COMMANDS MAWK(1)
NAME
mawk - pattern scanning and text processing language
SYNOPSIS
mawk [-F_s] 'program text' [file ...]
mawk [-F_s] -f program-file [file ...]
mawk -V
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 _n_e_w _a_w_k meaning it
implements the AWK language as defined in Aho, Kernighan and
Weinberger, _T_h_e _A_W_K _P_r_o_g_r_a_m_m_i_n_g _L_a_n_g_u_a_g_e, Addison-Wesley
Publishing, 1988. (Hereafter refered to as the AWK book.)
An AWK program is a sequence of _p_a_t_t_e_r_n {_a_c_t_i_o_n} 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 deter-
mined by the record separator variable, RS. Initially, RS =
"\n" and records are synonymous with lines. Each record is
compared against each _p_a_t_t_e_r_n and if it matches, the program
text for {_a_c_t_i_o_n} is executed.
OPTIONS
-F_s Set the field separator, FS, to string _s.
-f file
Read the program text from file instead of from the
command line.
-V mawk writes its version and copyright notice to stdout
and internal limits to stderr and exits 0. The inter-
nal limits can be changed by recompilation.
The -f option must be last and when the -V option is recog-
nized the rest of the command line is ignored.
THE AWK LANGUAGE
1. Program structure
An AWK program is a sequence of _p_a_t_t_e_r_n {_a_c_t_i_o_n} pairs and
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MAWK(1) USER COMMANDS MAWK(1)
user function definitions.
A pattern can be:
BEGIN
END
expression
/regular expression/
( pattern )
! pattern
pattern || pattern
pattern && pattern
pattern , pattern (a range pattern)
Range, BEGIN and END patterns cannot be combined with other
patterns. One, but not both, of _p_a_t_t_e_r_n {_a_c_t_i_o_n} can be
omitted. If {_a_c_t_i_o_n} is omitted it is implicitly { print
}. If _p_a_t_t_e_r_n 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 state-
ments 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 defini-
tion. A comment starts with # and extends to, but does not
include the end of line.
The following statements control program flow inside blocks.
if ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t
if ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t else _s_t_a_t_e_m_e_n_t
while ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t
do _s_t_a_t_e_m_e_n_t while ( _e_x_p_r )
for ( _o_p_t__e_x_p_r ; _o_p_t__e_x_p_r ; _o_p_t__e_x_p_r ) _s_t_a_t_e_m_e_n_t
for ( _v_a_r in _a_r_r_a_y ) _s_t_a_t_e_m_e_n_t
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
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MAWK(1) USER COMMANDS MAWK(1)
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.\n"
Strings can be continued across a line by escaping (\) the
newline. The following escape sequences are recognized.
\\ \
\" "
\a alert, ascii 7
\b backspace, ascii 8
\t tab, ascii 9
\n newline, ascii 10
\v vertical tab, ascii 11
\f formfeed, ascii 12
\r 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 _n_u_m_b_e_r
_a_n_d _s_t_r_i_n_g 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 _n_u_l_l,
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 statements
y = x + 2 ; z = x "hello"
The value stored in variable y will be typed numeric. If x
is not numeric, the value taken 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 necessary and concatenated
with "hello". (Of course, the value and type stored in x is
not changed by any conversions.) A string expression is con-
verted to numeric using its longest numeric prefix as with
_a_t_o_f(3). A numeric expression is converted to string by
replacing _e_x_p_r with sprintf( OFMT, _e_x_p_r). Sprintf() is an
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MAWK(1) USER COMMANDS MAWK(1)
AWK built-in that duplicates the functionality of
_s_p_r_i_n_t_f(3). Explicit type conversions can be forced, _e_x_p_r
"" is string and _e_x_p_r+0 is numeric.
To evaluate, _e_x_p_r1 rel-op _e_x_p_r2, 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 ( _e_x_p_r ) _s_t_a_t_e_m_e_n_t, a string
expression evaluates true if and only if it is not the empty
string ""; otherwise if and only if not numerically zero.
3. Regular expressions
In the AWK language, records, fields and strings are often
tested for matching a _r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n. Regular expres-
sions are enclosed in slashes, and
_e_x_p_r ~ /_r/
is an AWK expression that evaluates to 1 if _e_x_p_r "matches"
_r, which means a substring of _e_x_p_r 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 a pattern,
/_r/ { _a_c_t_i_o_n }
is the same as
$0 ~ /_r/ { _a_c_t_i_o_n }
and for each input record that matches _r, _a_c_t_i_o_n is exe-
cuted.
AWK uses extended regular expressions as with _e_g_r_e_p(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).
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MAWK(1) USER COMMANDS MAWK(1)
^ 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 expres-
sions as follows:
_r1_r2 matches _r1 followed immediately by _r2 (concatena-
tion).
_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, con-
catenation 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 recog-
nized 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 regu-
lar 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.
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MAWK(1) USER COMMANDS MAWK(1)
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 exam-
ple,
echo abc | mawk { gsub(//, "X") ; print }
XaXbXcX
4. Records and fields
Records are read in one at a time, and stored in the _f_i_e_l_d
variable $0. The record is split into _f_i_e_l_d_s 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
using 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 converted 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 functions. The identifier for a variable, array
or function can be a sequence of letters, digits and under-
scores, that does not start with a digit. Variables are not
declared; they exist when first referenced and are initial-
ized to _n_u_l_l.
New expressions are composed with the following operators in
order of increasing precedence.
_a_s_s_i_g_n_m_e_n_t = += -= *= /= %= ^=
_c_o_n_d_i_t_i_o_n_a_l ? :
_l_o_g_i_c_a_l _o_r ||
_l_o_g_i_c_a_l _a_n_d &&
_a_r_r_a_y _m_e_m_b_e_r_s_h_i_p in
_m_a_t_c_h_i_n_g ~ !~
_r_e_l_a_t_i_o_n_a_l < > <= >= == !=
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MAWK(1) USER COMMANDS MAWK(1)
_c_o_n_c_a_t_e_n_a_t_i_o_n (no explicit operator)
_a_d_d _o_p_s + -
_m_u_l _o_p_s * / %
_u_n_a_r_y + -
_l_o_g_i_c_a_l _n_o_t !
_e_x_p_o_n_e_n_t_i_a_t_i_o_n ^
_i_n_c _a_n_d _d_e_c ++ -- (both post and pre)
_f_i_e_l_d $
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 _a_r_r_a_y[_e_x_p_r]. Initially an array is empty; ele-
ments exist when first accessed. An expression, _e_x_p_r in
_a_r_r_a_y evaluates to 1 if _a_r_r_a_y[_e_x_p_r] exists, else to 0.
There is a form of the for statement that loops over each
element of an array.
for ( _v_a_r in _a_r_r_a_y ) _s_t_a_t_e_m_e_n_t
sets _v_a_r to each element of _a_r_r_a_y and executes _s_t_a_t_e_m_e_n_t.
The order of execution is not defined.
The statement, delete _a_r_r_a_y[_e_x_p_r], causes _a_r_r_a_y[_e_x_p_r] not to
exist.
Multidimensional arrays are synthesized with concatenation
using the built-in variable SUBSEP. _a_r_r_a_y[_e_x_p_r1,_e_x_p_r2] is
equivalent to _a_r_r_a_y[_e_x_p_r1 SUBSEP _e_x_p_r2]. Testing for a mul-
tidimensional 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.
FILENAME name of the current input file.
FNR current record number in FILENAME.
FS splits records into fields as a regular
expression.
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MAWK(1) USER COMMANDS MAWK(1)
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 =
"\n".
RLENGTH length set by the last call to the built-in
function, match().
RS input record separator, initially = "\n".
RSTART index set by the last call to match().
SUBSEP used to build multiple array subscripts, ini-
tially = "\034".
8. Built-in functions
String functions
gsub(_r,_s,_t) gsub(_r,_s)
Global substitution, every match of regular
expression _r in variable _t is replaced by string
_s. The number of replacements is returned. If _t
is omitted, $0 is used. An & in the replacement
string _s is replaced by the matched substring of
_t. \& puts a literal & in the replacement string.
index(_s,_t)
If _t is a substring of _s, then the position where
_t starts is returned, else 0 is returned. The
first character of _s is in position 1.
length(_s) length
Returns the length of string _s; without an argu-
ment, returns the length of $0.
match(_s,_r)
Returns the index of the first longest match of
regular expression _r in string _s. Returns 0 if no
match. As a side effect, RSTART is set to the
return value. RLENGTH is set to the length of the
match or -1 if no match. If the empty string is
matched, RLENGTH is set to 0, and 1 is returned if
the match is at the front, and length(_s)+1 is
Version 1.0 Last change: Sep 14 1991 8
MAWK(1) USER COMMANDS MAWK(1)
returned if the match is at the back.
split(_s,_A,_r) split(_s,_A)
String _s is split into fields by regular expres-
sion _r and the fields are loaded into array _A.
The number of fields is returned. See section 11
below for more detail. If _r is omitted, FS is
used.
sprintf(_f_o_r_m_a_t,_e_x_p_r-_l_i_s_t)
Returns a string constructed from _e_x_p_r-_l_i_s_t
according to _f_o_r_m_a_t. See the description of
printf() below.
sub(_r,_s,_t) sub(_r,_s)
Single substitution, same as gsub() except at most
one substitution.
substr(_s,_i,_n) substr(_s,_i)
Returns the substring of string _s, starting at
index _i, of length _n. If _n is omitted, the suffix
of _s, starting at _i is returned.
Arithmetic functions
atan2(_y,_x) Arctan of _y/_x between -pi and pi.
cos(_x) Cosine function, _x in radians.
exp(_x) Exponential function.
int(_x) Returns _x truncated towards zero.
log(_x) Natural logarithm.
rand() Returns a random number between zero and one.
sin(_x) Sine function, _x in radians.
sqrt(_x) Returns square root of _x.
srand(_e_x_p_r) srand()
Seeds the random number generator, using the clock
if _e_x_p_r is omitted, and returns the value of the
previous seed. mawk seeds the random number gen-
erator from the clock at startup so there is no
real need to call srand(). Srand(_e_x_p_r) is useful
for repeating pseudo random sequences.
9. Input and output
There are two output statements, print and printf.
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MAWK(1) USER COMMANDS MAWK(1)
print
writes $0 ORS to standard output.
print _e_x_p_r1, _e_x_p_r2, ..., _e_x_p_rn
writes _e_x_p_r1 OFS _e_x_p_r2 OFS ... _e_x_p_rn ORS to stan-
dard output.
printf _f_o_r_m_a_t, _e_x_p_r-_l_i_s_t
duplicates the printf C library function writing
to standard output. Supported conversions are %c,
%d, %e, %f, %g, %o and %x. -, width and .prec are
supported. Dynamic widths can be built using
string operations.
The output of print and printf can be redirected to a file
or command by appending > _f_i_l_e, >> _f_i_l_e or | _c_o_m_m_a_n_d to the
end of the print statement. Redirection opens _f_i_l_e or _c_o_m_-
_m_a_n_d only once, subsequent redirections append to the
already open stream. The argument list to print or printf
can optionally be enclosed in parentheses.
The input function getline has the following variations.
getline
reads $0, updates the fields, NF, NR and FNR.
getline < _f_i_l_e
reads $0 from _f_i_l_e, updates the fields and NF.
getline _v_a_r
reads the next record into _v_a_r, updates NR and
FNR.
getline _v_a_r < _f_i_l_e
reads the next record of _f_i_l_e into _v_a_r.
_c_o_m_m_a_n_d | getline
pipes a record from _c_o_m_m_a_n_d into $0 and updates
the fields and NF.
_c_o_m_m_a_n_d | getline _v_a_r
pipes a record from _c_o_m_m_a_n_d into _v_a_r.
Getline returns 0 on end-of-file, -1 on error, otherwise 1.
_C_o_m_m_a_n_d is executed by /bin/sh.
The function close(_e_x_p_r) closes the file or pipe associated
with _e_x_p_r. Close returns 0 or -1 if _e_x_p_r is not associated
with an open stream. Close() is used to reread a file or
command, make sure the other end of an output pipe is fin-
ished or conserve file resources.
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MAWK(1) USER COMMANDS MAWK(1)
The function system(_e_x_p_r) uses /bin/sh to execute _e_x_p_r and
returns the exit status of the command _e_x_p_r.
10. User defined functions
The syntax for a user defined function is
function name( _a_r_g_s ) { _s_t_a_t_e_m_e_n_t_s }
The function body can contain a return statement
return _o_p_t__e_x_p_r
A return statement is not required. Function calls may be
nested or recursive. Functions are passed expressions by
value and arrays by reference. Extra arguments serve as
local variables and are initialized to _n_u_l_l. For example,
csplit(_s,_A) puts each character of _s into array _A and
returns the length of _s.
function csplit(s, A, n, i)
{
n = length(s)
for( i = 1 ; i <= n ; i++ ) A[i] = substr(s, i, 1)
return n
}
Putting extra space between passed arguments and local vari-
ables is conventional. Functions can be referenced before
they are defined, but the function name and the '(' of the
arguments must touch to avoid confusion with concatenation.
11. Splitting strings, records and files
Awk programs use the same algorithm to split strings into
arrays with split(), and records into fields on FS. mawk
uses essentially the same algorithm to split files into
records on RS.
Split(_e_x_p_r,_A,_s_e_p) works as follows:
(1) If _s_e_p is omitted, it is replaced by FS. _S_e_p can
be an expression or regular expression. If it is
an expression of non-string type, it is converted
to string.
(2) If _s_e_p = " " (a single space), then <SPACE> is
trimmed from the front and back of _e_x_p_r, and _s_e_p
becomes <SPACE>. mawk defines <SPACE> as the reg-
ular expression /[ \t\r\n]+/. Otherwise _s_e_p is
treated as a regular expression, except that
meta-characters are ignored for a string of length
1, e.g., split(x, A, "*") and split(x, A, /\*/)
are the same.
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MAWK(1) USER COMMANDS MAWK(1)
(3) If _e_x_p_r is not string, it is converted to string.
If _e_x_p_r is then the empty string "", split()
returns 0 and _A is unchanged. Otherwise, all
non-overlapping, non-null and longest matches of
_s_e_p in _e_x_p_r, separate _e_x_p_r into fields which are
loaded into _A. The fields are placed in A[1],
A[2], ..., A[n] and split() returns n, the number
of fields which is the number of matches plus one.
Data placed in _A that looks numeric is typed
number and string.
Splitting records into fields works the same except the
pieces are loaded into $1, $2,..., $NF. If $0 is empty, NF
is set to 0 and all $i to "".
mawk splits files into records by the same algorithm, but
with the slight difference that RS is really a terminator
instead of a separator. (ORS is really a terminator too).
E.g., if FS = ":+" and $0 = "a::b:" , then NF = 3 and
$1 = "a", $2 = "b" and $3 = "", but if "a::b:" is the
contents of an input file and RS = ":+", then there are
two records "a" and "b".
RS = " " is not special.
12. Multi-line records
Since mawk interprets RS as a regular expression, multi-line
records are easy. Setting RS = "\n\n+", makes one or more
blank lines separate records. If FS = " " (the default),
then single newlines, by the rules for <SPACE> above, become
space and single newlines are field separators.
For example, if a file is "a b\nc\n\n", RS = "\n\n+"
and FS = " ", then there is one record "a b\nc" with
three fields "a", "b" and "c". Changing FS = "\n",
gives two fields "a b" and "c"; changing FS = "", gives
one field identical to the record.
If you want lines with spaces or tabs to be considered
blank, set RS = "\n([ \t]*\n)+". For compatibility with
other awks, setting RS = "" has the same effect on determin-
ing records as RS = "\n\n+". (This interpretation makes
mawk picky that the input not start with blank lines and
that the last record is fully terminated with at least two
newlines.)
Most of the time when you change RS for multi-line records,
you will also want to change ORS to "\n\n" so the record
spacing is preserved on output.
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MAWK(1) USER COMMANDS MAWK(1)
13. Program execution
This section describes the order of program execution.
First ARGC is set to the total number of command line argu-
ments passed to the execution phase of the program. ARGV[0]
is set the name of the AWK interpreter and ARGV[1] ...
ARGV[ARGC-1] holds the remaining command line arguments
exclusive of options and program source. For example with
mawk -f prog v=1 A t=hello B
ARGC = 5 with ARGV[0] = "mawk", ARGV[1] = "v=1", ARGV[2] =
"A", ARGV[3] = "t=hello" and ARGV[4] = "B".
Next, each BEGIN block is executed in order. If the program
consists entirely of BEGIN blocks, then execution ter-
minates, else an input stream is opened and execution con-
tinues. If ARGC equals 1, the input stream is set to stdin,
else the command line arguments ARGV[1] ... ARGV[ARGC-1]
are examined for a file argument.
The command line arguments divide into three sets: file
arguments, assignment arguments and empty strings "". An
assignment has the form _v_a_r=_s_t_r_i_n_g. When an ARGV[i] is
examined as a possible file argument, if it is empty it is
skipped; if it is an assignment argument, the assignment to
_v_a_r takes place and i skips to the next argument; else
ARGV[i] is opened for input. If it fails to open, execution
terminates with exit code 1. If no command line argument is
a file argument, then input comes from stdin. Getline in a
BEGIN action opens input. "-" as a file argument denotes
stdin.
Once an input stream is open, each input record is tested
against each _p_a_t_t_e_r_n, and if it matches, the associated
_a_c_t_i_o_n is executed. An expression pattern matches if it is
boolean true (see the end of section 2). A regular expres-
sion pattern matches if $0 matches the regular expression.
A BEGIN pattern matches before any input has been read, and
an END pattern matches after all input has been read. A
range pattern, _p_a_t1,_p_a_t2 , matches every record between the
match of _p_a_t1 and the match _p_a_t2 inclusively.
When end of file occurs on the input stream, the remaining
command line arguments are examined for a file argument, and
if there is one it is opened, else the END _p_a_t_t_e_r_n is con-
sidered matched and all END _a_c_t_i_o_n_s are executed.
In the example, the assignment v=1 takes place after the
BEGIN _a_c_t_i_o_n_s are executed, and the data placed in v is
typed number and string. Input is then read from file A.
On end of file A, t is set to the string "hello", and B is
opened for input. On end of file B, the END _a_c_t_i_o_n_s are
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MAWK(1) USER COMMANDS MAWK(1)
executed.
Program flow at the _p_a_t_t_e_r_n {_a_c_t_i_o_n} level can be changed
with the
next and
exit _o_p_t__e_x_p_r
statements. A next statement causes the next input record
to be read and pattern testing to restart with the first
_p_a_t_t_e_r_n {_a_c_t_i_o_n} pair in the program. An exit statement
causes immediate execution of the END actions or program
termination if there are none or if the exit occurs in an
END action. The _o_p_t__e_x_p_r sets the exit value of the program
unless overridden by a later exit or subsequent error.
EXAMPLES
1. emulate cat.
{ print }
2. emulate wc.
{ chars += length($0) + 1 # add one for the \n
words += NF
}
END{ print NR, words, chars }
3. count the number of unique "real words".
BEGIN { FS = "[^A-Za-z]+" }
{ for(i = 1 ; i <= NF ; i++) word[$i] = "" }
END { delete word[""]
for ( i in word ) cnt++
print cnt
}
4. sum the second field of every record based on the first
field.
$1 ~ /credit|gain/ { sum += $2 }
$1 ~ /debit|loss/ { sum -= $2 }
END { print sum }
5. sort a file, comparing as string
{ line[NR] = $0 "" } # make sure of comparison type
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MAWK(1) USER COMMANDS MAWK(1)
# in case some lines look numeric
END { isort(line, NR)
for(i = 1 ; i <= NR ; i++) print line[i]
}
#insertion sort of A[1..n]
function isort( A, n, i, j, hold)
{
for( i = 2 ; i <= n ; i++)
{
hold = A[j = i]
while ( A[j-1] > hold )
{ j-- ; A[j+1] = A[j] }
A[j] = hold
}
# sentinel A[0] = "" will be created if needed
}
COMPATIBILITY ISSUES
mawk and SystemVR3 nawk (new awk) implement the AWK language
as described in the AWK book. SystemVR4 nawk, with influ-
ence from GNU gawk, added a few features that are now speci-
fied in the draft 11.1 POSIX standard for awk, most notably,
functions toupper() and tolower(), and access to the
environment through an array, ENVIRON[].
With mawk, the following are all equivalent,
x ~ /a\+b/ x ~ "a\+b" x ~ "a\\+b"
The strings get scanned twice, once as string and once as
regular expression. On the string scan, mawk ignores the
escape on non-escape characters while the AWK book advocates
_\_c be recognized as _c which necessitates the double escaping
of meta-characters in strings. For programs that must run
under a variety of awks, the more portable but less read-
able, double escape should be used.
POSIX AWK is oriented to operate on files a line at a time.
RS can be changed from "\n" to another single character, but
it is hard to find any use for this - there are no examples
in the AWK book. By convention, RS = "", makes one or more
blank lines separate records, allowing multi-line records.
When RS = "", "\n" is always a field separator regardless of
the value in FS.
mawk, on the other hand, allows RS to be a regular expres-
sion. When "\n" appears in records, it is treated as space,
and FS always determines fields. RS = "" is treated the
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MAWK(1) USER COMMANDS MAWK(1)
same as RS = "\n\n+".
Removing the line at a time paradigm can make some programs
simplier and can often improve performance. For example,
redoing example 3 from above,
BEGIN { RS = "[^A-Za-z]+" }
{ word[ $0 ] = "" }
END { delete word[ "" ]
for( i in word ) cnt++
print cnt
}
counts the number of unique words by making each word a
record. On moderate size files, mawk executes twice as
fast, because of the simplified inner loop.
The following program replaces each comment by a single
space in a C program file,
BEGIN {
RS = "/\*([^*]|\*+[^/*])*\*+/"
# comment is record separator
ORS = " "
getline hold
}
{ print hold ; hold = $0 }
END { printf "%s" , hold }
Buffering one record is needed to avoid terminating the last
record with a space.
Finally, here is how mawk handles exceptional cases not dis-
cussed in the AWK book or the POSIX draft. It is unsafe to
assume consistency across awks and safe to skip to the next
section.
substr(s, i, n) returns the characters of s in the
intersection of the closed interval [1, length(s)] and
the half-open interval [i, i+n). When this intersec-
tion is empty, the empty string is returned; so
substr("ABC", 1, 0) = "" and substr("ABC", -4, 6) =
"A".
Every string, including the empty string, matches the
empty string at the front so, s ~ // and s ~ "", are
always 1 as is match(s, //) and match(s, ""). The last
two set RLENGTH to 0.
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MAWK(1) USER COMMANDS MAWK(1)
index(s, t) is always the same as match(s, t1) where t1
is the same as t with metacharacters escaped. Hence
consistency with match requires that index(s, "")
always returns 1. Also the condition, index(s,t) != 0
if and only t is a substring of s, requires
index("","") = 1.
If getline encounters end of file, getline var, leaves
var unchanged. Similarly, on entry to the END actions,
$0, the fields and NF have their value unaltered from
the last record.
DIAGNOSTICS
A previously undiscussed option -D causes mawk to _d_u_m_p to
stderr an assembler like listing of its internal representa-
tion of the program which is linear byte code for a virtual
stack machine.
SEE ALSO
_e_g_r_e_p (1)
Aho, Kernighan and Weinberger, _T_h_e _A_W_K _P_r_o_g_r_a_m_m_i_n_g _L_a_n_g_u_a_g_e,
Addison-Wesley Publishing, 1988, (the AWK book), defines the
language, opening with a tutorial and advancing to many
interesting programs that delve into issues of software
design and analysis relevant to programming in any language.
_T_h_e _G_A_W_K _M_a_n_u_a_l, The Free Software Foundation, 1991, is a
tutorial and language reference that does not attempt the
depth of the AWK book and assumes the reader may be a novice
programmer. The section on AWK arrays is excellent. It also
discusses POSIX requirements for AWK.
BUGS
mawk cannot handle ascii NUL \0 in the source or data files.
You can output NUL using printf with %c, and any other 8 bit
character is acceptable input.
Implementors of the AWK language have shown a consistent
lack of imagination when naming their programs.
AUTHOR
Mike Brennan (brennan@boeing.com).
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