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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 experi-
menting with algorithms. mawk is a new awk meaning it implements the AWK language as de-
fined in Aho, Kernighan and Weinberger, The AWK Programming Language, Addison-Wesley Pub-
lishing, 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 interpre-
tation. 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 = "\n" 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. Im-
plementation specific options are prefaced with -W. mawk provides these:
-W dump writes an assembler like listing of the internal representation of the pro-
gram to stdout and exits 0 (on successful compilation).
-W exec file Program text is read from file and this is the last option.
This is a useful alternative to -f on systems that support the #! "magic
number" convention for executable scripts. Those implicitly pass the path-
name of the script itself as the final parameter, and expect no more than
one "-" option on the #! line. Because mawk can combine multiple -W op-
tions separated by commas, you can use this option when an additional -W
option is needed.
-W help prints a usage message to stderr and exits (same as "-W usage").
-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 posix_space forces mawk not to consider '\n' to be space.
-W random=num calls srand with the given parameter (and overrides the auto-seeding behav-
ior).
-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 usage prints a usage message to stderr and exits (same as "-W help").
-W version mawk writes its version and copyright to stdout and compiled limits to
stderr and exits 0.
mawk accepts abbreviations for any of these options, e.g., "-W v" and "-Wv" both tell mawk
to show its version.
mawk allows multiple -W options to be combined by separating the options with commas,
e.g., -Wsprint=2000,posix. This is useful for executable #! "magic number" invocations
in which only one argument is supported, e.g., -Winteractive,exec.
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 im-
plicitly { 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 def-
inition. 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.\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 number and string which has both a
numeric value and a string value at the same time. User defined variables come into exis-
tence 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 oc-
curs 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 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 nec-
essary 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 long-
est numeric prefix as with atof(3). A numeric expression is converted to string by re-
placing expr with sprintf(CONVFMT, expr), unless expr can be represented on the host ma-
chine 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 conversion 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 the -E option of grep(1). The regular ex-
pression 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 charac-
ters 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. Assign-
ment to a field with index greater than NF, increases NF and causes $0 to be recon-
structed.
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 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 prece-
dence.
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 ele-
ment and the actual index is "1". Arrays indexed by strings are called associative ar-
rays. Initially 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 ex-
tension, 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 = "\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, initially = "\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 re-
placed 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 sub-
string of t. \& and \\ put literal & and \, respectively, 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)
Returns the length of string or array. s.
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 returned if the match is at the back.
split(s,A,r) split(s,A)
String s is split into fields by regular expression 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(format,expr-list)
Returns a string constructed from expr-list according to format. See the de-
scription 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.
tolower(s)
Returns a copy of s with all upper case characters converted to lower case.
toupper(s)
Returns a copy of s with all lower case characters converted to upper case.
Time functions
These are available on systems which support the corresponding C mktime and strftime func-
tions:
mktime(specification)
converts a date specification to a timestamp with the same units as systime.
The date specification is a string containing the components of the date as
decimal integers:
YYYY
the year, e.g., 2012
MM the month of the year starting at 1
DD the day of the month starting at 1
HH hour (0-23)
MM minute (0-59)
SS seconds (0-59)
DST
tells how to treat timezone versus daylight savings time:
positive
DST is in effect
zero (default)
DST is not in effect
negative
mktime() should (use timezone information and system databases to) at-
tempt to determine whether DST is in effect at the specified time.
strftime([format [, timestamp [, utc ]]])
formats the given timestamp using the format (passed to the C strftime func-
tion):
o If the format parameter is missing, "%c" is used.
o If the timestamp parameter is missing, the current value from systime is
used.
o If the utc parameter is present and nonzero, the result is in UTC. Other-
wise local time is used.
systime()
returns the current time of day as the number of seconds since the Epoch
(1970-01-01 00:00:00 UTC on POSIX systems).
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(expr) srand()
Seeds the random number generator, using the clock if expr is omitted, and re-
turns the value of the previous seed. Srand(expr) is useful for repeating
pseudo random sequences.
Note: mawk is normally configured to seed the random number generator from the
clock at startup, making it unnecessary to call srand(). This feature can be
suppressed via conditional compile, or overridden using the -Wrandom option.
9. Input and output
There are two output statements, print and printf.
print writes $0 ORS to standard output.
print expr1, expr2, ..., exprn
writes expr1 OFS expr2 OFS ... exprn ORS to standard output. Numeric expres-
sions are converted to string with OFMT.
printf format, expr-list
duplicates the printf C library function writing to standard output. The com-
plete ANSI C format specifications are recognized with conversions %c, %d, %e,
%E, %f, %g, %G, %i, %o, %s, %u, %x, %X and %%, and conversion qualifiers h and
l.
The argument list to print or printf can optionally be enclosed in parentheses. Print
formats numbers using OFMT or "%d" for exact integers. "%c" with a numeric argument
prints the corresponding 8 bit character, with a string argument it prints the first char-
acter of the string. The output of print and printf can be redirected to a file or com-
mand by appending > file, >> file or | command to the end of the print statement. Redi-
rection opens file or command only once, subsequent redirections append to the already
open stream. By convention, mawk associates the filename
o "/dev/stderr" with stderr,
o "/dev/stdout" with stdout,
o "-" and "/dev/stdin" with stdin.
The association with stderr is especially useful because it allows print and printf to be
redirected to stderr. These names can also be passed to functions.
The input function getline has the following variations.
getline
reads into $0, updates the fields, NF, NR and FNR.
getline < file
reads into $0 from file, updates the fields and NF.
getline var
reads the next record into var, updates NR and FNR.
getline var < file
reads the next record of file into var.
command | getline
pipes a record from command into $0 and updates the fields and NF.
command | getline var
pipes a record from command into var.
Getline returns 0 on end-of-file, -1 on error, otherwise 1.
Commands on the end of pipes are executed by /bin/sh.
The function close(expr) closes the file or pipe associated with expr. Close returns 0 if
expr is an open file, the exit status if expr is a piped command, and -1 otherwise. Close
is used to reread a file or command, make sure the other end of an output pipe is finished
or conserve file resources.
The function fflush(expr) flushes the output file or pipe associated with expr. Fflush
returns 0 if expr is an open output stream else -1. Fflush without an argument flushes
stdout. Fflush with an empty argument ("") flushes all open output.
The function system(expr) uses the C runtime system call to execute expr and returns the
corresponding wait status of the command as follows:
o if the system call failed, setting the status to -1, mawk returns that value.
o if the command exited normally, mawk returns its exit-status.
o if the command exited due to a signal such as SIGHUP, mawk returns the signal number
plus 256.
Changes made to the ENVIRON array are not passed to commands executed with system or
pipes.
10. User defined functions
The syntax for a user defined function is
function name( args ) { statements }
The function body can contain a return statement
return opt_expr
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 null. 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 variables is conventional. Func-
tions can be referenced before they are defined, but the function name and the '(' of the
arguments must touch to avoid confusion with concatenation.
A function parameter is normally a scalar value (number or string). If there is a forward
reference to a function using an array as a parameter, the function's corresponding param-
eter will be treated as an array.
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(expr,A,sep) works as follows:
(1) If sep is omitted, it is replaced by FS. Sep can be an expression or regular ex-
pression. If it is an expression of non-string type, it is converted to string.
(2) If sep = " " (a single space), then <SPACE> is trimmed from the front and back of
expr, and sep becomes <SPACE>. mawk defines <SPACE> as the regular expression
/[ \t\n]+/. Otherwise sep 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.
(3) If expr is not string, it is converted to string. If expr is then the empty
string "", split() returns 0 and A is set empty. Otherwise, all non-overlapping,
non-null and longest matches of sep in expr, separate expr 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.
If FS = "", then mawk breaks the record into individual characters, and, similarly,
split(s,A,"") places the individual characters of s into A.
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
o a file is "a b\nc\n\n",
o RS = "\n\n+" and
o FS = " ",
then there is one record "a b\nc" with three fields "a", "b" and "c":
o Changing FS = "\n", gives two fields "a b" and "c";
o 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 as if blank lines
are stripped from the front and back of files and then records are determined as if RS =
"\n\n+". POSIX requires that "\n" always separates records when RS = "" regardless of the
value of FS. mawk does not support this convention, because defining "\n" as <SPACE>
makes it unnecessary.
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.
13. Program execution
This section describes the order of program execution. First ARGC is set to the total
number of command line arguments 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 com-
mand 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 terminates, else an input stream is opened and execution continues.
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 var=string. When an ARGV[i] is examined
as a possible file argument, if it is empty it is skipped; if it is an assignment argu-
ment, the assignment to var 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 2. If no com-
mand 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 pattern, and if it
matches, the associated action is executed. An expression pattern matches if it is bool-
ean true (see the end of section 2). A BEGIN pattern matches before any input has been
read, and an END pattern matches after all input has been read. A range pattern,
expr1,expr2 , matches every record between the match of expr1 and the match expr2 inclu-
sively.
When end of file occurs on the input stream, the remaining command line arguments are ex-
amined for a file argument, and if there is one it is opened, else the END pattern is con-
sidered matched and all END actions are executed.
In the example, the assignment v=1 takes place after the BEGIN actions 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 actions are executed.
Program flow at the pattern {action} level can be changed with the
next
nextfile
exit opt_expr
statements:
o A next statement causes the next input record to be read and pattern testing to
restart with the first pattern {action} pair in the program.
o A nextfile statement tells mawk to stop processing the current input file. It then
updates FILENAME to the next file listed on the command line, and resets FNR to 1.
o 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 opt_expr 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
# 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 1.3.3 versus POSIX 1003.2 Draft 11.3
The POSIX 1003.2(draft 11.3) definition of the AWK language is AWK as described in the AWK
book with a few extensions that appeared in SystemVR4 nawk. The extensions are:
o New functions: toupper() and tolower().
o New variables: ENVIRON[] and CONVFMT.
o ANSI C conversion specifications for printf() and sprintf().
o New command options: -v var=value, multiple -f options and implementation options
as arguments to -W.
o For systems (MS-DOS or Windows) which provide a setmode function, an environment
variable MAWKBINMODE and a built-in variable BINMODE. The bits of the BINMODE
value tell mawk how to modify the RS and ORS variables:
0 set standard input to binary mode, and if BIT-2 is unset, set RS to "\r\n"
(CR/LF) rather than "\n" (LF).
1 set standard output to binary mode, and if BIT-2 is unset, set ORS to "\r\n"
(CR/LF) rather than "\n" (LF).
2 suppress the assignment to RS and ORS of CR/LF, making it possible to run
scripts and generate output compatible with Unix line-endings.
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 exam-
ples 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 re-
gardless of the value in FS.
mawk, on the other hand, allows RS to be a regular expression. When "\n" appears in
records, it is treated as space, and FS always determines fields.
Removing the line at a time paradigm can make some programs simpler 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.
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. POSIX explicitly declines to define the behavior which passively forces programs
that must run under a variety of awks to use the more portable but less readable, double
escape.
POSIX AWK does not recognize "/dev/std{in,out,err}". Some systems provide an actual de-
vice for this, allowing AWKs which do not implement the feature directly to support it.
POSIX AWK does not recognize \x hex escape sequences in strings. Unlike ANSI C, mawk lim-
its the number of digits that follows \x to two as the current implementation only sup-
ports 8 bit characters. The built-in fflush first appeared in a recent (1993) AT&T awk
released to netlib, and is not part of the POSIX standard. Aggregate deletion with delete
array is not part of the POSIX standard.
POSIX explicitly leaves the behavior of FS = "" undefined, and mentions splitting the
record into characters as a possible interpretation, but currently this use is not porta-
ble across implementations.
Random numbers
POSIX does not prescribe a method for initializing random numbers at startup.
In practice, most implementations do nothing special, which makes srand and rand follow
the C runtime library, making the initial seed value 1. Some implementations (Solaris
XPG4 and Tru64) return 0 from the first call to srand, although the results from rand be-
have as if the initial seed is 1. Other implementations return 1.
While mawk can call srand at startup with no parameter (initializing random numbers from
the clock), this feature may be suppressed using conditional compilation.
Extensions added for compatibility for GAWK and BWK
Nextfile is a gawk extension (also implemented by BWK awk), is not yet part of the POSIX
standard (as of October 2012), although it has been accepted for the next revision of the
standard.
Mktime, strftime and systime are gawk extensions.
The "/dev/stdin" feature was added to mawk after 1.3.4, for compatibility with gawk and
BWK awk. The corresponding "-" (alias for /dev/stdin) was present in mawk 1.3.3.
Subtle Differences not in POSIX or the AWK Book
Finally, here is how mawk handles exceptional cases not discussed in the AWK book or the
POSIX draft. It is unsafe to assume consistency across awks and safe to skip to the next
section.
o substr(s, i, n) returns the characters of s in the intersection of the closed in-
terval [1, length(s)] and the half-open interval [i, i+n). When this intersection
is empty, the empty string is returned; so substr("ABC", 1, 0) = "" and sub-
str("ABC", -4, 6) = "A".
o 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.
o 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.
o 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.
ENVIRONMENT VARIABLES
Mawk recognizes these variables:
MAWKBINMODE
(see COMPATIBILITY ISSUES)
MAWK_LONG_OPTIONS
If this is set, mawk uses its value to decide what to do with GNU-style long op-
tions:
allow Mawk allows the option to be checked against the (small) set of long op-
tions it recognizes.
error Mawk prints an error message and exits. This is the default.
ignore Mawk ignores the option.
warn Print an warning message and otherwise ignore the option.
If the variable is unset, mawk prints an error message and exits.
WHINY_USERS
This is an undocumented gawk feature. It tells mawk to sort array indices before it
starts to iterate over the elements of an array.
SEE ALSO
grep(1)
Aho, Kernighan and Weinberger, The AWK Programming Language, 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.
The GAWK Manual, 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 implements printf() and sprintf() using the C library functions, printf and sprintf,
so full ANSI compatibility requires an ANSI C library. In practice this means the h con-
version qualifier may not be available. Also mawk inherits any bugs or limitations of the
library functions.
Implementors of the AWK language have shown a consistent lack of imagination when naming
their programs.
AUTHOR
Mike Brennan (brennan AT whidbey.com).
Thomas E. Dickey <dickey AT invisible-island.net>.
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