Ничего не знал об этой команде в Linux, но пробовать некогда. Как бы не забыть. Потому здесь просто длиннющая распечатка man awk
In [2]:
!man awk
MAWK(1) USER COMMANDS MAWK(1)
N NA AM ME E
mawk - pattern scanning and text processing language
S SY YN NO OP PS SI IS S
m ma aw wk k [-W W _ o_ p_ t_ i_ o_ n] [-F F _ v_ a_ l_ u_ e] [-v v _ v_ a_ r_ =_ v_ a_ l_ u_ e] [--] 'program text' [file ...]
m ma aw wk k [-W W _ o_ p_ t_ i_ o_ n] [-F F _ v_ a_ l_ u_ e] [-v v _ v_ a_ r_ =_ v_ a_ l_ u_ e] [-f f _ p_ r_ o_ g_ r_ a_ m_ -_ f_ i_ l_ e] [--] [file ...]
D DE ES SC CR RI IP PT TI IO ON N
m ma aw wk k 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. m ma aw wk k
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 referred to as the AWK book.) m ma aw wk k
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 m ma aw wk k provides a small number of extensions.
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 determined by
the record separator variable, R RS S. Initially, R RS S = "\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.
O OP PT TI IO ON NS S
-F F _ v_ a_ l_ u_ e sets the field separator, F FS S, to _ v_ a_ l_ u_ e.
-f f _ f_ i_ l_ e Program text is read from _ f_ i_ l_ e instead of from the command line. Multiple - -f f options are
allowed.
-v v _ v_ a_ r_ =_ v_ a_ l_ u_ e assigns _ v_ a_ l_ u_ e to program variable _ v_ a_ r.
-- 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 W. m ma aw wk k provides six:
-W W version m ma aw wk k writes its version and copyright to stdout and compiled limits to stderr and exits 0.
-W W dump writes an assembler like listing of the internal representation of the program to stdout
and exits 0 (on successful compilation).
-W W interactive sets unbuffered writes to stdout and line buffered reads from stdin. Records from stdin
are lines regardless of the value of R RS S.
-W W exec _ f_ i_ l_ e Program text is read from _ f_ i_ l_ e and this is the last option. Useful on systems that support
the # #! ! "magic number" convention for executable scripts.
-W W sprintf=_ n_ u_ m adjusts the size of m ma aw wk k' 's s internal sprintf buffer to _ n_ u_ m bytes. More than rare use of
this option indicates m ma aw wk k should be recompiled.
-W W posix_space forces m ma aw wk k not to consider '\n' to be space.
The short forms - -W W[vdiesp] are recognized and on some systems - -W We is mandatory to avoid command line
length limitations.
T TH HE E A AW WK K L LA AN NG GU UA AG GE E
1 1. . P Pr ro og gr ra am m s st tr ru uc ct tu ur re e
An AWK program is a sequence of _ p_ a_ t_ t_ e_ r_ n _ {_ a_ c_ t_ i_ o_ n_ } pairs and user function definitions.
A pattern can be:
B BE EG GI IN N
E EN ND D
expression
expression , expression
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. B BE EG GI IN N and E EN ND D 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 contin‐
ued with a backslash, \. A statement can be broken without a backslash after a comma, left brace, &&,
||, d do o, e el ls se e, the right parenthesis of an i if f, w wh hi il le e or f fo or r 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.
i if f ( _ e_ x_ p_ r ) _ s_ t_ a_ t_ e_ m_ e_ n_ t
i if f ( _ e_ x_ p_ r ) _ s_ t_ a_ t_ e_ m_ e_ n_ t e el ls se e _ s_ t_ a_ t_ e_ m_ e_ n_ t
w wh hi il le e ( _ e_ x_ p_ r ) _ s_ t_ a_ t_ e_ m_ e_ n_ t
d do o _ s_ t_ a_ t_ e_ m_ e_ n_ t w wh hi il le e ( _ e_ x_ p_ r )
f fo or r ( _ 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
f fo or r ( _ v_ a_ r i in n _ a_ r_ r_ a_ y ) _ s_ t_ a_ t_ e_ m_ e_ n_ t
c co on nt ti in nu ue e
b br re ea ak k
2 2. . D Da at ta a t ty yp pe es s, , c co on nv ve er rs si io on n a an nd d c co om mp pa ar ri is so on n
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., m ma aw wk k 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 sec‐
tion 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 read from x is con‐
verted 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 s sp pr ri in nt tf f( (C CO ON NV VF FM MT T, _ e_ x_ p_ r), unless _ e_ x_ p_ r can be represented on the host machine
as an exact integer then it is converted to s sp pr ri in nt tf f("%d", _ e_ x_ p_ r). S Sp pr ri in nt tf f( () ) is an AWK built-in that
duplicates the functionality of _ s_ p_ r_ i_ n_ t_ f(3), and C CO ON NV VF FM MT T is a built-in variable used for internal conver‐
sion from number to string and initialized to "%.6g". 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 r re el l- -o op p _ 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, i if f ( _ 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 ""; numeric values if and only if not numerically zero.
3 3. . R Re eg gu ul la ar r e ex xp pr re es ss si io on ns s
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 expressions 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 pattern-action pairs,
/_ r/ { _ a_ c_ t_ i_ o_ n } and $ $0 0 ~ /_ r/ { _ a_ c_ t_ i_ o_ n }
are the same, and for each input record that matches _ r, _ a_ c_ t_ i_ o_ n is executed. In fact, /_ r/ is an AWK
expression that is equivalent to ($ $0 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 _ 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).
^ 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:
_ r1_ r2 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.
m ma aw wk k 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 4. . R Re ec co or rd ds s a an nd d f fi ie el ld ds s
Records are read in one at a time, and stored in the _ f_ i_ e_ l_ d variable $ $0 0. The record is split into _ f_ i_ e_ l_ d_ s
which are stored in $ $1 1, $ $2 2, ..., $ $N NF F. The built-in variable N NF F is set to the number of fields, and N NR R
and F FN NR R are incremented by 1. Fields above $ $N NF F are set to "".
Assignment to $ $0 0 causes the fields and N NF F to be recomputed. Assignment to N NF F or to a field causes $ $0 0 to
be reconstructed by concatenating the $ $i i' 's s separated by O OF FS S. Assignment to a field with index greater
than N NF F, increases N NF F and causes $ $0 0 to be reconstructed.
Data input stored in fields is string, unless the entire field has numeric form and then the type is num‐
ber and string. For example,
echo 24 24E |
mawk '{ print($1>100, $1>"100", $2>100, $2>"100") }'
0 1 1 1
$ $0 0 and $ $2 2 are string and $ $1 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 5. . E Ex xp pr re es ss si io on ns s a an nd d o op pe er ra at to or rs s
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 _ 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 i in n
_ m_ a_ t_ c_ h_ i_ n_ g ~ !~
_ r_ e_ l_ a_ t_ i_ o_ n_ a_ l < > <= >= == !=
_ 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 6. . A Ar rr ra ay ys s
Awk provides one-dimensional arrays. Array elements are expressed as _ a_ r_ r_ a_ y[_ e_ x_ p_ r]. _ E_ x_ p_ r 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. Initially an array is empty; elements
exist when first accessed. An expression, _ e_ x_ p_ r i in n _ 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 f fo or r statement that loops over each index of an array.
f fo or r ( _ v_ a_ r i in n _ a_ r_ r_ a_ y ) _ s_ t_ a_ t_ e_ m_ e_ n_ t
sets _ v_ a_ r to each index of _ a_ r_ r_ a_ y and executes _ s_ t_ a_ t_ e_ m_ e_ n_ t. The order that _ v_ a_ r transverses the indices of
_ a_ r_ r_ a_ y is not defined.
The statement, d de el le et te e _ a_ r_ r_ a_ y[_ e_ x_ p_ r], causes _ a_ r_ r_ a_ y[_ e_ x_ p_ r] not to exist. m ma aw wk k supports an extension, d de el le et te e
_ a_ r_ r_ a_ y, which deletes all elements of _ a_ r_ r_ a_ y.
Multidimensional arrays are synthesized with concatenation using the built-in variable S SU UB BS SE EP P.
_ 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 S SU UB BS SE EP P _ e_ x_ p_ r2]. Testing for a multidimensional element
uses a parenthesized index, such as
if ( (i, j) in A ) print A[i, j]
7 7. . B Bu ui il lt ti in n- -v va ar ri ia ab bl le es s
The following variables are built-in and initialized before program execution.
A AR RG GC C number of command line arguments.
A AR RG GV V array of command line arguments, 0..ARGC-1.
C CO ON NV VF FM MT T format for internal conversion of numbers to string, initially = "%.6g".
E EN NV VI IR RO ON N array indexed by environment variables. An environment string, _ v_ a_ r_ =_ v_ a_ l_ u_ e is stored as
E EN NV VI IR RO ON N[_ v_ a_ r] = _ v_ a_ l_ u_ e.
F FI IL LE EN NA AM ME E name of the current input file.
F FN NR R current record number in F FI IL LE EN NA AM ME E.
F FS S splits records into fields as a regular expression.
N NF F number of fields in the current record.
N NR R current record number in the total input stream.
O OF FM MT T format for printing numbers; initially = "%.6g".
O OF FS S inserted between fields on output, initially = " ".
O OR RS S terminates each record on output, initially = "\n".
R RL LE EN NG GT TH H length set by the last call to the built-in function, m ma at tc ch h( () ).
R RS S input record separator, initially = "\n".
R RS ST TA AR RT T index set by the last call to m ma at tc ch h( () ).
S SU UB BS SE EP P used to build multiple array subscripts, initially = "\034".
8 8. . B Bu ui il lt t- -i in n f fu un nc ct ti io on ns s
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 0 is used. An & in
the replacement string _ s is replaced by the matched substring 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 _ 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, R RS ST TA AR RT T is set to the return value. R RL LE EN NG GT TH H is set to the
length of the match or -1 if no match. If the empty string is matched, R RL LE EN NG GT TH H 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 omit‐
ted, F FS S 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.
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.
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. m ma aw wk k seeds the random number generator 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 9. . I In np pu ut t a an nd d o ou ut tp pu ut t
There are two output statements, p pr ri in nt t and p pr ri in nt tf f.
print writes $ $0 0 O OR RS S to standard output.
print _ e_ x_ p_ r1, _ e_ x_ p_ r2, ..., _ e_ x_ p_ rn
writes _ e_ x_ p_ r1 O OF FS S _ e_ x_ p_ r2 O OF FS S ... _ e_ x_ p_ rn O OR RS S to standard output. Numeric expressions are con‐
verted to string with O OF FM MT T.
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. The complete 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 O OF FM MT T or "%d" for exact integers. "%c" with a numeric argument prints the corresponding 8 bit char‐
acter, with a string argument it prints the first character of the string. 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. By convention, m ma aw wk k associates the filename "/dev/stderr" with stderr which allows
print and printf to be redirected to stderr. m ma aw wk k also associates "-" and "/dev/stdout" with stdin and
stdout which allows these streams to be passed to functions.
The input function g ge et tl li in ne e has the following variations.
getline
reads into $ $0 0, updates the fields, N NF F, N NR R and F FN NR R.
getline < _ f_ i_ l_ e
reads into $ $0 0 from _ f_ i_ l_ e, updates the fields and N NF F.
getline _ v_ a_ r
reads the next record into _ v_ a_ r, updates N NR R and F FN NR R.
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 0 and updates the fields and N NF F.
_ 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.
Commands on the end of pipes are executed by /bin/sh.
The function c cl lo os se e(_ e_ x_ p_ r) closes the file or pipe associated with _ e_ x_ p_ r. Close returns 0 if _ e_ x_ p_ r is an
open file, the exit status if _ e_ x_ p_ r 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 f ff fl lu us sh h(_ e_ x_ p_ r) flushes the output file or pipe associated with _ e_ x_ p_ r. Fflush returns 0 if _ e_ x_ p_ r
is an open output stream else -1. Fflush without an argument flushes stdout. Fflush with an empty argu‐
ment ("") flushes all open output.
The function s sy ys st te em m(_ 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.
Changes made to the E EN NV VI IR RO ON N array are not passed to commands executed with s sy ys st te em m or pipes.
1 10 0. . U Us se er r d de ef fi in ne ed d f fu un nc ct ti io on ns s
The syntax for a user defined function is
f fu un nc ct ti io on n name( _ a_ r_ g_ s ) { _ s_ t_ a_ t_ e_ m_ e_ n_ t_ s }
The function body can contain a return statement
r re et tu ur rn n _ 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 initial‐
ized 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 variables is conventional. Functions can be ref‐
erenced before they are defined, but the function name and the '(' of the arguments must touch to avoid
confusion with concatenation.
1 11 1. . S Sp pl li it tt ti in ng g s st tr ri in ng gs s, , r re ec co or rd ds s a an nd d f fi il le es s
Awk programs use the same algorithm to split strings into arrays with split(), and records into fields on
F FS S. m ma aw wk k uses essentially the same algorithm to split files into records on R RS S.
Split(_ e_ x_ p_ r_ ,_ A_ ,_ s_ e_ p) works as follows:
(1) If _ s_ e_ p is omitted, it is replaced by F FS S. _ 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>. m ma aw wk k defines <SPACE> as the regular expression /[ \t\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.
(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 set empty. 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 1, $ $2 2,..., $ $N NF F. If $ $0 0 is
empty, N NF F is set to 0 and all $ $i i to "".
m ma aw wk k splits files into records by the same algorithm, but with the slight difference that R RS S is really a
terminator instead of a separator. (O OR RS S is really a terminator too).
E.g., if F FS S = ":+" and $ $0 0 = "a::b:" , then N NF F = 3 and $ $1 1 = "a", $ $2 2 = "b" and $ $3 3 = "", but if
"a::b:" is the contents of an input file and R RS S = ":+", then there are two records "a" and "b".
R RS S = " " is not special.
If F FS S = "", then m ma aw wk k breaks the record into individual characters, and, similarly, split(_ s_ ,_ A_ ,"") places
the individual characters of _ s into _ A.
1 12 2. . M Mu ul lt ti i- -l li in ne e r re ec co or rd ds s
Since m ma aw wk k interprets R RS S as a regular expression, multi-line records are easy. Setting R RS S = "\n\n+",
makes one or more blank lines separate records. If F FS S = " " (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", R RS S = "\n\n+" and F FS S = " ", then there is one record
"a b\nc" with three fields "a", "b" and "c". Changing F FS S = "\n", gives two fields "a b" and "c";
changing F FS S = "", gives one field identical to the record.
If you want lines with spaces or tabs to be considered blank, set R RS S = "\n([ \t]*\n)+". For compatibil‐
ity with other awks, setting R RS S = "" has the same effect as if blank lines are stripped from the front
and back of files and then records are determined as if R RS S = "\n\n+". Posix requires that "\n" always
separates records when R RS S = "" regardless of the value of F FS S. m ma aw wk k does not support this convention,
because defining "\n" as <SPACE> makes it unnecessary.
Most of the time when you change R RS S for multi-line records, you will also want to change O OR RS S to "\n\n" so
the record spacing is preserved on output.
1 13 3. . P Pr ro og gr ra am m e ex xe ec cu ut ti io on n
This section describes the order of program execution. First A AR RG GC C is set to the total number of command
line arguments passed to the execution phase of the program. A AR RG GV V[ [0 0] ] is set the name of the AWK inter‐
preter and A AR RG GV V[ [1 1] ] ... A AR RG GV V[ [A AR RG GC C- -1 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
A AR RG GC C = 5 with A AR RG GV V[ [0 0] ] = "mawk", A AR RG GV V[ [1 1] ] = "v=1", A AR RG GV V[ [2 2] ] = "A", A AR RG GV V[ [3 3] ] = "t=hello" and A AR RG GV V[ [4 4] ] = "B".
Next, each B BE EG GI IN N block is executed in order. If the program consists entirely of B BE EG GI IN N blocks, then exe‐
cution terminates, else an input stream is opened and execution continues. If A AR RG GC C equals 1, the input
stream is set to stdin, else the command line arguments A AR RG GV V[ [1 1] ] ... A AR RG GV V[ [A AR RG GC C- -1 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 A AR RG GV V[ [i 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 i skips
to the next argument; else A AR RG GV V[ [i i] ] is opened for input. If it fails to open, execution terminates with
exit code 2. If no command line argument is a file argument, then input comes from stdin. Getline in a
B BE EG GI IN N 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 sec‐
tion 2). A B BE EG GI IN N pattern matches before any input has been read, and an E EN ND D pattern matches after all
input has been read. A range pattern, _ e_ x_ p_ r1,_ e_ x_ p_ r2 , matches every record between the match of _ e_ x_ p_ r1 and
the match _ e_ x_ p_ r2 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 E EN ND D _ p_ a_ t_ t_ e_ r_ n is considered matched and all E EN ND D
_ a_ c_ t_ i_ o_ n_ s are executed.
In the example, the assignment v=1 takes place after the B BE EG GI IN N _ 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 E EN ND D _ a_ c_ t_ i_ o_ n_ s are executed.
Program flow at the _ p_ a_ t_ t_ e_ r_ n _ {_ a_ c_ t_ i_ o_ n_ } level can be changed with the
n ne ex xt t
e ex xi it t _ o_ p_ t_ __ e_ x_ p_ r
statements. A n ne ex xt t 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 e ex xi it t statement causes immediate execution of the E EN ND D
actions or program termination if there are none or if the e ex xi it t occurs in an E EN ND D action. The _ o_ p_ t_ __ e_ x_ p_ r
sets the exit value of the program unless overridden by a later e ex xi it t or subsequent error.
E EX XA AM MP PL LE ES S
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
}
C CO OM MP PA AT TI IB BI IL LI IT TY Y I IS SS SU UE ES S
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:
New functions: toupper() and tolower().
New variables: ENVIRON[] and CONVFMT.
ANSI C conversion specifications for printf() and sprintf().
New command options: -v var=value, multiple -f options and implementation options as arguments to
-W.
Posix AWK is oriented to operate on files a line at a time. R RS S can be changed from "\n" to another sin‐
gle character, but it is hard to find any use for this — there are no examples in the AWK book. By con‐
vention, R RS S = "", makes one or more blank lines separate records, allowing multi-line records. When R RS S =
"", "\n" is always a field separator regardless of the value in F FS S.
m ma aw wk k, on the other hand, allows R RS S to be a regular expression. When "\n" appears in records, it is
treated as space, and F FS S 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, m ma aw wk k 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 m ma aw wk k, 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, m ma aw wk k
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{out,err}" or \x hex escape sequences in strings. Unlike ANSI C,
m ma aw wk k limits the number of digits that follows \x to two as the current implementation only supports 8 bit
characters. The built-in f ff fl lu us sh h first appeared in a recent (1993) AT&T awk released to netlib, and is
not part of the posix standard. Aggregate deletion with d de el le et te e _ a_ r_ r_ a_ y is not part of the posix standard.
Posix explicitly leaves the behavior of F FS S = "" undefined, and mentions splitting the record into charac‐
ters as a possible interpretation, but currently this use is not portable across implementations.
Finally, here is how m ma aw wk k 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.
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 intersection 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 R RL LE EN NG GT TH H to 0.
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 con‐
dition, 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
E EN ND D actions, $ $0 0, the fields and N NF F have their value unaltered from the last record.
S SE EE E A AL LS SO O
_ 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.
B BU UG GS S
m ma aw wk k 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.
m ma aw wk k 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 conversion qualifier may not be
available. Also m ma aw wk k 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.
A AU UT TH HO OR R
Mike Brennan (brennan@whidbey.com).
Version 1.2 Dec 22 1994 MAWK(1)
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