4.4BSD/usr/share/man/cat1/awk.0
AWK(1) Utility Commands AWK(1)
NNAAMMEE
awk - pattern scanning and processing language
SSYYNNOOPPSSIISS
aawwkk [ POSIX or GNU style options ] --ff _p_r_o_g_r_a_m_-_f_i_l_e [ ---- ]
file ...
aawwkk [ POSIX or GNU style options ] [ ---- ] _p_r_o_g_r_a_m_-_t_e_x_t
file ...
DDEESSCCRRIIPPTTIIOONN
_G_a_w_k is the GNU Project's implementation of the AWK pro-
gramming language. In the 4.4BSD distribution, it is
installed as _a_w_k. It conforms to the definition of the
language in the POSIX 1003.2 Command Language And Utili-
ties Standard. This version in turn is based on the
description in _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, by Aho,
Kernighan, and Weinberger, with the additional features
defined in the System V Release 4 version of UNIX _a_w_k.
_G_a_w_k also provides some GNU-specific extensions.
The command line consists of options to _g_a_w_k itself, the
AWK program text (if not supplied via the --ff or ----ffiillee
options), and values to be made available in the AARRGGCC and
AARRGGVV pre-defined AWK variables.
OOPPTTIIOONNSS
_G_a_w_k options may be either the traditional POSIX one let-
ter options, or the GNU style long options. POSIX style
options start with a single ``-'', while GNU long options
start with ``--''. GNU style long options are provided
for both GNU-specific features and for POSIX mandated fea-
tures. Other implementations of the AWK language are
likely to only accept the traditional one letter options.
Following the POSIX standard, _g_a_w_k-specific options are
supplied via arguments to the --WW option. Multiple --WW
options may be supplied, or multiple arguments may be sup-
plied together if they are separated by commas, or
enclosed in quotes and separated by white space. Case is
ignored in arguments to the --WW option. Each --WW option has
a corresponding GNU style long option, as detailed below.
_G_a_w_k accepts the following options.
--FF _f_s
----ffiieelldd--sseeppaarraattoorr==_f_s
Use _f_s for the input field separator (the value of
the FFSS predefined variable).
--vv _v_a_r==_v_a_l
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AWK(1) Utility Commands AWK(1)
----aassssiiggnn==_v_a_r==_v_a_l
Assign the value _v_a_l, to the variable _v_a_r, before
execution of the program begins. Such variable
values are available to the BBEEGGIINN block of an AWK
program.
--ff _p_r_o_g_r_a_m_-_f_i_l_e
----ffiillee==_p_r_o_g_r_a_m_-_f_i_l_e
Read the AWK program source from the file _p_r_o_g_r_a_m_-
_f_i_l_e, instead of from the first command line argu-
ment. Multiple --ff (or ----ffiillee) options may be used.
--WW ccoommppaatt
----ccoommppaatt Run in _c_o_m_p_a_t_i_b_i_l_i_t_y mode. In compatibility
mode, _g_a_w_k behaves identically to UNIX _a_w_k;
none of the GNU-specific extensions are recog-
nized. See GGNNUU EEXXTTEENNSSIIOONNSS, below, for more
information.
--WW ccooppyylleefftt
--WW ccooppyyrriigghhtt
----ccooppyylleefftt
----ccooppyyrriigghhtt Print the short version of the GNU copyright
information message on the standard error out-
put.
--WW hheellpp
--WW uussaaggee
----hheellpp
----uussaaggee Print a relatively short summary of the avail-
able options on the standard error output.
--WW lliinntt
----lliinntt Provide warnings about constructs that are
dubious or non-portable to other AWK implemen-
tations.
--WW ppoossiixx
----ppoossiixx This turns on _c_o_m_p_a_t_i_b_i_l_i_t_y mode, with the
following additional restrictions:
+o \\xx escape sequences are not recognized.
+o The synonym ffuunncc for the keyword ffuunnccttiioonn is
not recognized.
+o The operators **** and ****== cannot be used in
place of ^^ and ^^==.
--WW ssoouurrccee==_p_r_o_g_r_a_m_-_t_e_x_t
----ssoouurrccee==_p_r_o_g_r_a_m_-_t_e_x_t
Use _p_r_o_g_r_a_m_-_t_e_x_t as AWK program source code.
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AWK(1) Utility Commands AWK(1)
This option allows the easy intermixing of
library functions (used via the --ff and ----ffiillee
options) with source code entered on the com-
mand line. It is intended primarily for
medium to large size AWK programs used in
shell scripts.
The --WW ssoouurrccee== form of this option uses the
rest of the command line argument for _p_r_o_g_r_a_m_-
_t_e_x_t; no other options to --WW will be recog-
nized in the same argument.
--WW vveerrssiioonn
----vveerrssiioonn Print version information for this particular
copy of _g_a_w_k on the standard error output.
This is useful mainly for knowing if the cur-
rent copy of _g_a_w_k on your system is up to date
with respect to whatever the Free Software
Foundation is distributing.
---- Signal the end of options. This is useful to
allow further arguments to the AWK program
itself to start with a ``-''. This is mainly
for consistency with the argument parsing con-
vention used by most other POSIX programs.
Any other options are flagged as illegal, but are other-
wise ignored.
AAWWKK PPRROOGGRRAAMM EEXXEECCUUTTIIOONN
An AWK program consists of a sequence of pattern-action
statements and optional function definitions.
_p_a_t_t_e_r_n {{ _a_c_t_i_o_n _s_t_a_t_e_m_e_n_t_s }}
ffuunnccttiioonn _n_a_m_e((_p_a_r_a_m_e_t_e_r _l_i_s_t)) {{ _s_t_a_t_e_m_e_n_t_s }}
_G_a_w_k first reads the program source from the _p_r_o_g_r_a_m_-
_f_i_l_e(s) if specified, or from the first non-option argu-
ment on the command line. The --ff option may be used mul-
tiple times on the command line. _G_a_w_k will read the pro-
gram text as if all the _p_r_o_g_r_a_m_-_f_i_l_es had been concate-
nated together. This is useful for building libraries of
AWK functions, without having to include them in each new
AWK program that uses them. To use a library function in
a file from a program typed in on the command line, spec-
ify //ddeevv//ttttyy as one of the _p_r_o_g_r_a_m_-_f_i_l_es, type your pro-
gram, and end it with a ^^DD (control-d).
The environment variable AAWWKKPPAATTHH specifies a search path
to use when finding source files named with the --ff option.
If this variable does not exist, the default path is
""..:://uussrr//lliibb//aawwkk:://uussrr//llooccaall//lliibb//aawwkk"". If a file name given
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AWK(1) Utility Commands AWK(1)
to the --ff option contains a ``/'' character, no path
search is performed.
_G_a_w_k executes AWK programs in the following order. First,
_g_a_w_k compiles the program into an internal form. Next,
all variable assignments specified via the --vv option are
performed. Then, _g_a_w_k executes the code in the BBEEGGIINN
block(s) (if any), and then proceeds to read each file
named in the AARRGGVV array. If there are no files named on
the command line, _g_a_w_k reads the standard input.
If a filename on the command line has the form _v_a_r==_v_a_l it
is treated as a variable assignment. The variable _v_a_r will
be assigned the value _v_a_l. (This happens after any BBEEGGIINN
block(s) have been run.) Command line variable assignment
is most useful for dynamically assigning values to the
variables AWK uses to control how input is broken into
fields and records. It is also useful for controlling
state if multiple passes are needed over a single data
file.
If the value of a particular element of AARRGGVV is empty
(""""), _g_a_w_k skips over it.
For each line in the input, _g_a_w_k tests to see if it
matches any _p_a_t_t_e_r_n in the AWK program. For each pattern
that the line matches, the associated _a_c_t_i_o_n is executed.
The patterns are tested in the order they occur in the
program.
Finally, after all the input is exhausted, _g_a_w_k executes
the code in the EENNDD block(s) (if any).
VVAARRIIAABBLLEESS AANNDD FFIIEELLDDSS
AWK variables are dynamic; they come into existence when
they are first used. Their values are either floating-
point numbers or strings, or both, depending upon how they
are used. AWK also has one dimensional arrays; multiply
dimensioned arrays may be simulated. Several pre-defined
variables are set as a program runs; these will be
described as needed and summarized below.
FFiieellddss
As each input line is read, _g_a_w_k splits the line into
_f_i_e_l_d_s, using the value of the FFSS variable as the field
separator. If FFSS is a single character, fields are sepa-
rated by that character. Otherwise, FFSS is expected to be
a full regular expression. In the special case that FFSS is
a single blank, fields are separated by runs of blanks
and/or tabs. Note that the value of IIGGNNOORREECCAASSEE (see
below) will also affect how fields are split when FFSS is a
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AWK(1) Utility Commands AWK(1)
regular expression.
If the FFIIEELLDDWWIIDDTTHHSS variable is set to a space separated
list of numbers, each field is expected to have fixed
width, and _g_a_w_k will split up the record using the speci-
fied widths. The value of FFSS is ignored. Assigning a new
value to FFSS overrides the use of FFIIEELLDDWWIIDDTTHHSS, and restores
the default behavior.
Each field in the input line may be referenced by its
position, $$11, $$22, and so on. $$00 is the whole line. The
value of a field may be assigned to as well. Fields need
not be referenced by constants:
nn == 55
pprriinntt $$nn
prints the fifth field in the input line. The variable NNFF
is set to the total number of fields in the input line.
References to non-existent fields (i.e., fields after $$NNFF)
produce the null-string. However, assigning to a non-
existent field (e.g., $$((NNFF++22)) == 55) will increase the value
of NNFF, create any intervening fields with the null string
as their value, and cause the value of $$00 to be recom-
puted, with the fields being separated by the value of
OOFFSS.
BBuuiilltt--iinn VVaarriiaabblleess
AWK's built-in variables are:
AARRGGCC The number of command line arguments (does not
include options to _g_a_w_k, or the program
source).
AARRGGIINNDD The index in AARRGGVV of the current file being
processed.
AARRGGVV Array of command line arguments. The array is
indexed from 0 to AARRGGCC - 1. Dynamically
changing the contents of AARRGGVV can control the
files used for data.
CCOONNVVFFMMTT The conversion format for numbers, ""%%..66gg"", by
default.
EENNVVIIRROONN An array containing the values of the current
environment. The array is indexed by the
environment variables, each element being the
value of that variable (e.g., EENNVVIIRROONN[[""HHOOMMEE""]]
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AWK(1) Utility Commands AWK(1)
might be //uu//aarrnnoolldd). Changing this array does
not affect the environment seen by programs
which _g_a_w_k spawns via redirection or the ssyyss--
tteemm(()) function. (This may change in a future
version of _g_a_w_k.)
EERRRRNNOO If a system error occurs either doing a redi-
rection for ggeettlliinnee, during a read for ggeett--
lliinnee, or during a cclloossee, then EERRRRNNOO will con-
tain a string describing the error.
FFIIEELLDDWWIIDDTTHHSS A white-space separated list of fieldwidths.
When set, _g_a_w_k parses the input into fields of
fixed width, instead of using the value of the
FFSS variable as the field separator. The fixed
field width facility is still experimental;
expect the semantics to change as _g_a_w_k evolves
over time.
FFIILLEENNAAMMEE The name of the current input file. If no
files are specified on the command line, the
value of FFIILLEENNAAMMEE is ``-''.
FFNNRR The input record number in the current input
file.
FFSS The input field separator, a blank by default.
IIGGNNOORREECCAASSEE Controls the case-sensitivity of all regular
expression operations. If IIGGNNOORREECCAASSEE has a
non-zero value, then pattern matching in
rules, field splitting with FFSS, regular
expression matching with ~~ and !!~~, and the
ggssuubb(()), iinnddeexx(()), mmaattcchh(()), sspplliitt(()), and ssuubb(())
pre-defined functions will all ignore case
when doing regular expression operations.
Thus, if IIGGNNOORREECCAASSEE is not equal to zero, //aaBB//
matches all of the strings ""aabb"", ""aaBB"", ""AAbb"",
and ""AABB"". As with all AWK variables, the ini-
tial value of IIGGNNOORREECCAASSEE is zero, so all regu-
lar expression operations are normally case-
sensitive.
NNFF The number of fields in the current input
record.
NNRR The total number of input records seen so far.
OOFFMMTT The output format for numbers, ""%%..66gg"", by
default.
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AWK(1) Utility Commands AWK(1)
OOFFSS The output field separator, a blank by
default.
OORRSS The output record separator, a newline by
default.
RRSS The input record separator, a newline by
default. RRSS is exceptional in that only the
first character of its string value is used
for separating records. (This will probably
change in a future release of _g_a_w_k.) If RRSS is
set to the null string, then records are sepa-
rated by blank lines. When RRSS is set to the
null string, then the newline character always
acts as a field separator, in addition to
whatever value FFSS may have.
RRSSTTAARRTT The index of the first character matched by
mmaattcchh(()); 0 if no match.
RRLLEENNGGTTHH The length of the string matched by mmaattcchh(());
-1 if no match.
SSUUBBSSEEPP The character used to separate multiple sub-
scripts in array elements, ""\\003344"" by default.
AArrrraayyss
Arrays are subscripted with an expression between square
brackets ([[ and ]]). If the expression is an expression
list (_e_x_p_r, _e_x_p_r ...) then the array subscript is a
string consisting of the concatenation of the (string)
value of each expression, separated by the value of the
SSUUBBSSEEPP variable. This facility is used to simulate multi-
ply dimensioned arrays. For example:
ii == ""AA"" ;; jj == ""BB"" ;; kk == ""CC""
xx[[ii,, jj,, kk]] == ""hheelllloo,, wwoorrlldd\\nn""
assigns the string ""hheelllloo,, wwoorrlldd\\nn"" to the element of the
array xx which is indexed by the string ""AA\\003344BB\\003344CC"". All
arrays in AWK are associative, i.e., indexed by string
values.
The special operator iinn may be used in an iiff or wwhhiillee
statement to see if an array has an index consisting of a
particular value.
iiff ((vvaall iinn aarrrraayy))
pprriinntt aarrrraayy[[vvaall]]
If the array has multiple subscripts, use ((ii,, jj)) iinn aarrrraayy.
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AWK(1) Utility Commands AWK(1)
The iinn construct may also be used in a ffoorr loop to iterate
over all the elements of an array.
An element may be deleted from an array using the ddeelleettee
statement.
VVaarriiaabbllee TTyyppiinngg AAnndd CCoonnvveerrssiioonn
Variables and fields may be (floating point) numbers, or
strings, or both. How the value of a variable is inter-
preted depends upon its context. If used in a numeric
expression, it will be treated as a number, if used as a
string it will be treated as a string.
To force a variable to be treated as a number, add 0 to
it; to force it to be treated as a string, concatenate it
with the null string.
When a string must be converted to a number, the conver-
sion is accomplished using _a_t_o_f(3). A number is converted
to a string by using the value of CCOONNVVFFMMTT as a format
string for _s_p_r_i_n_t_f(3), with the numeric value of the vari-
able as the argument. However, even though all numbers in
AWK are floating-point, integral values are _a_l_w_a_y_s con-
verted as integers. Thus, given
CCOONNVVFFMMTT == ""%%22..22ff""
aa == 1122
bb == aa """"
the variable bb has a value of ""1122"" and not ""1122..0000"".
_G_a_w_k performs comparisons as follows: If two variables are
numeric, they are compared numerically. If one value is
numeric and the other has a string value that is a
``numeric string,'' then comparisons are also done numeri-
cally. Otherwise, the numeric value is converted to a
string and a string comparison is performed. Two strings
are compared, of course, as strings. According to the
POSIX standard, even if two strings are numeric strings, a
numeric comparison is performed. However, this is clearly
incorrect, and _g_a_w_k does not do this.
Uninitialized variables have the numeric value 0 and the
string value "" (the null, or empty, string).
PPAATTTTEERRNNSS AANNDD AACCTTIIOONNSS
AWK is a line oriented language. The pattern comes first,
and then the action. Action statements are enclosed in {{
and }}. Either the pattern may be missing, or the action
may be missing, but, of course, not both. If the pattern
is missing, the action will be executed for every single
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AWK(1) Utility Commands AWK(1)
line of input. A missing action is equivalent to
{{ pprriinntt }}
which prints the entire line.
Comments begin with the ``#'' character, and continue
until the end of the line. Blank lines may be used to
separate statements. Normally, a statement ends with a
newline, however, this is not the case for lines ending in
a ``,'', ``{'', ``?'', ``:'', ``&&'', or ``||''. Lines
ending in ddoo or eellssee also have their statements automati-
cally continued on the following line. In other cases, a
line can be continued by ending it with a ``\'', in which
case the newline will be ignored.
Multiple statements may be put on one line by separating
them with a ``;''. This applies to both the statements
within the action part of a pattern-action pair (the usual
case), and to the pattern-action statements themselves.
PPaatttteerrnnss
AWK patterns may be one of the following:
BBEEGGIINN
EENNDD
//_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n//
_r_e_l_a_t_i_o_n_a_l _e_x_p_r_e_s_s_i_o_n
_p_a_t_t_e_r_n &&&& _p_a_t_t_e_r_n
_p_a_t_t_e_r_n |||| _p_a_t_t_e_r_n
_p_a_t_t_e_r_n ?? _p_a_t_t_e_r_n :: _p_a_t_t_e_r_n
((_p_a_t_t_e_r_n))
!! _p_a_t_t_e_r_n
_p_a_t_t_e_r_n_1,, _p_a_t_t_e_r_n_2
BBEEGGIINN and EENNDD are two special kinds of patterns which are
not tested against the input. The action parts of all
BBEEGGIINN patterns are merged as if all the statements had
been written in a single BBEEGGIINN block. They are executed
before any of the input is read. Similarly, all the EENNDD
blocks are merged, and executed when all the input is
exhausted (or when an eexxiitt statement is executed). BBEEGGIINN
and EENNDD patterns cannot be combined with other patterns in
pattern expressions. BBEEGGIINN and EENNDD patterns cannot have
missing action parts.
For //_r_e_g_u_l_a_r _e_x_p_r_e_s_s_i_o_n// patterns, the associated state-
ment is executed for each input line that matches the reg-
ular expression. Regular expressions are the same as
those in _e_g_r_e_p(1), and are summarized below.
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AWK(1) Utility Commands AWK(1)
A _r_e_l_a_t_i_o_n_a_l _e_x_p_r_e_s_s_i_o_n may use any of the operators
defined below in the section on actions. These generally
test whether certain fields match certain regular expres-
sions.
The &&&&, ||||, and !! operators are logical AND, logical OR,
and logical NOT, respectively, as in C. They do short-
circuit evaluation, also as in C, and are used for combin-
ing more primitive pattern expressions. As in most lan-
guages, parentheses may be used to change the order of
evaluation.
The ??:: operator is like the same operator in C. If the
first pattern is true then the pattern used for testing is
the second pattern, otherwise it is the third. Only one of
the second and third patterns is evaluated.
The _p_a_t_t_e_r_n_1,, _p_a_t_t_e_r_n_2 form of an expression is called a
range pattern. It matches all input records starting with
a line that matches _p_a_t_t_e_r_n_1, and continuing until a
record that matches _p_a_t_t_e_r_n_2, inclusive. It does not com-
bine with any other sort of pattern expression.
RReegguullaarr EExxpprreessssiioonnss
Regular expressions are the extended kind found in _e_g_r_e_p.
They are composed of characters as follows:
_c matches the non-metacharacter _c.
_\_c matches the literal character _c.
.. matches any character except newline.
^^ matches the beginning of a line or a string.
$$ matches the end of a line or a string.
[[_a_b_c_._._.]] character class, matches any of the characters
_a_b_c_._._..
[[^^_a_b_c_._._.]] negated character class, matches any character
except _a_b_c_._._. and newline.
_r_1||_r_2 alternation: matches either _r_1 or _r_2.
_r_1_r_2 concatenation: matches _r_1, and then _r_2.
_r++ matches one or more _r's.
_r** matches zero or more _r's.
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AWK(1) Utility Commands AWK(1)
_r?? matches zero or one _r's.
((_r)) grouping: matches _r.
The escape sequences that are valid in string constants
(see below) are also legal in regular expressions.
AAccttiioonnss
Action statements are enclosed in braces, {{ and }}. Action
statements consist of the usual assignment, conditional,
and looping statements found in most languages. The opera-
tors, control statements, and input/output statements
available are patterned after those in C.
OOppeerraattoorrss
The operators in AWK, in order of increasing precedence,
are
== ++== --==
**== //== %%== ^^== Assignment. Both absolute assignment ((_v_a_r ==
_v_a_l_u_e)) and operator-assignment (the other
forms) are supported.
??:: The C conditional expression. This has the
form _e_x_p_r_1 ?? _e_x_p_r_2 :: _e_x_p_r_3. If _e_x_p_r_1 is true,
the value of the expression is _e_x_p_r_2, other-
wise it is _e_x_p_r_3. Only one of _e_x_p_r_2 and _e_x_p_r_3
is evaluated.
|||| Logical OR.
&&&& Logical AND.
~~ !!~~ Regular expression match, negated match.
NNOOTTEE:: Do not use a constant regular expression
(//ffoooo//) on the left-hand side of a ~~ or !!~~.
Only use one on the right-hand side. The
expression //ffoooo// ~~ _e_x_p has the same meaning as
(((($$00 ~~ //ffoooo//)) ~~ _e_x_p)). This is usually _n_o_t
what was intended.
<< >>
<<== >>==
!!== ==== The regular relational operators.
_b_l_a_n_k String concatenation.
++ -- Addition and subtraction.
** // %% Multiplication, division, and modulus.
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AWK(1) Utility Commands AWK(1)
++ -- !! Unary plus, unary minus, and logical negation.
^^ Exponentiation (**** may also be used, and ****==
for the assignment operator).
++++ ---- Increment and decrement, both prefix and post-
fix.
$$ Field reference.
CCoonnttrrooll SSttaatteemmeennttss
The control statements are as follows:
iiff ((_c_o_n_d_i_t_i_o_n)) _s_t_a_t_e_m_e_n_t [ eellssee _s_t_a_t_e_m_e_n_t ]
wwhhiillee ((_c_o_n_d_i_t_i_o_n)) _s_t_a_t_e_m_e_n_t
ddoo _s_t_a_t_e_m_e_n_t wwhhiillee ((_c_o_n_d_i_t_i_o_n))
ffoorr ((_e_x_p_r_1;; _e_x_p_r_2;; _e_x_p_r_3)) _s_t_a_t_e_m_e_n_t
ffoorr ((_v_a_r iinn _a_r_r_a_y)) _s_t_a_t_e_m_e_n_t
bbrreeaakk
ccoonnttiinnuuee
ddeelleettee _a_r_r_a_y[[_i_n_d_e_x]]
eexxiitt [ _e_x_p_r_e_s_s_i_o_n ]
{{ _s_t_a_t_e_m_e_n_t_s }}
II//OO SSttaatteemmeennttss
The input/output statements are as follows:
cclloossee((_f_i_l_e_n_a_m_e)) Close file (or pipe, see below).
ggeettlliinnee Set $$00 from next input record; set
NNFF, NNRR, FFNNRR.
ggeettlliinnee <<_f_i_l_e Set $$00 from next record of _f_i_l_e; set
NNFF.
ggeettlliinnee _v_a_r Set _v_a_r from next input record; set
NNFF, FFNNRR.
ggeettlliinnee _v_a_r <<_f_i_l_e Set _v_a_r from next record of _f_i_l_e.
nneexxtt Stop processing the current input
record. The next input record is
read and processing starts over with
the first pattern in the AWK pro-
gram. If the end of the input data
is reached, the EENNDD block(s), if
any, are executed.
nneexxtt ffiillee Stop processing the current input
file. The next input record read
Free Software Foundation April 15 1993 12
AWK(1) Utility Commands AWK(1)
comes from the next input file.
FFIILLEENNAAMMEE is updated, FFNNRR is reset to
1, and processing starts over with
the first pattern in the AWK pro-
gram. If the end of the input data
is reached, the EENNDD block(s), if
any, are executed.
pprriinntt Prints the current record.
pprriinntt _e_x_p_r_-_l_i_s_t Prints expressions.
pprriinntt _e_x_p_r_-_l_i_s_t >>_f_i_l_e Prints expressions on _f_i_l_e.
pprriinnttff _f_m_t_, _e_x_p_r_-_l_i_s_t Format and print.
pprriinnttff _f_m_t_, _e_x_p_r_-_l_i_s_t >>_f_i_l_e
Format and print on _f_i_l_e.
ssyysstteemm((_c_m_d_-_l_i_n_e)) Execute the command _c_m_d_-_l_i_n_e, and
return the exit status. (This may
not be available on non-POSIX sys-
tems.)
Other input/output redirections are also allowed. For
pprriinntt and pprriinnttff, >>>>_f_i_l_e appends output to the _f_i_l_e, while
|| _c_o_m_m_a_n_d writes on a pipe. In a similar fashion, _c_o_m_m_a_n_d
|| ggeettlliinnee pipes into ggeettlliinnee. GGeettlliinnee will return 0 on
end of file, and -1 on an error.
TThhee _p_r_i_n_t_f SSttaatteemmeenntt
The AWK versions of the pprriinnttff statement and sspprriinnttff(())
function (see below) accept the following conversion spec-
ification formats:
%%cc An ASCII character. If the argument used for %%cc is
numeric, it is treated as a character and printed.
Otherwise, the argument is assumed to be a string,
and the only first character of that string is
printed.
%%dd A decimal number (the integer part).
%%ii Just like %%dd.
%%ee A floating point number of the form
[[--]]dd..ddddddddddddEE[[++--]]dddd.
%%ff A floating point number of the form [[--]]dddddd..dddddddddddd.
%%gg Use ee or ff conversion, whichever is shorter, with
Free Software Foundation April 15 1993 13
AWK(1) Utility Commands AWK(1)
nonsignificant zeros suppressed.
%%oo An unsigned octal number (again, an integer).
%%ss A character string.
%%xx An unsigned hexadecimal number (an integer).
%%XX Like %%xx, but using AABBCCDDEEFF instead of aabbccddeeff.
%%%% A single %% character; no argument is converted.
There are optional, additional parameters that may lie
between the %% and the control letter:
-- The expression should be left-justified within its
field.
_w_i_d_t_h The field should be padded to this width. If the
number has a leading zero, then the field will be
padded with zeros. Otherwise it is padded with
blanks.
.._p_r_e_c A number indicating the maximum width of strings or
digits to the right of the decimal point.
The dynamic _w_i_d_t_h and _p_r_e_c capabilities of the ANSI C
pprriinnttff(()) routines are supported. A ** in place of either
the wwiiddtthh or pprreecc specifications will cause their values
to be taken from the argument list to pprriinnttff or sspprriinnttff(()).
SSppeecciiaall FFiillee NNaammeess
When doing I/O redirection from either pprriinntt or pprriinnttff
into a file, or via ggeettlliinnee from a file, _g_a_w_k recognizes
certain special filenames internally. These filenames
allow access to open file descriptors inherited from
_g_a_w_k's parent process (usually the shell). Other special
filenames provide access information about the running
ggaawwkk process. The filenames are:
//ddeevv//ppiidd Reading this file returns the process ID of
the current process, in decimal, terminated
with a newline.
//ddeevv//ppppiidd Reading this file returns the parent process
ID of the current process, in decimal, termi-
nated with a newline.
//ddeevv//ppggrrppiidd Reading this file returns the process group ID
of the current process, in decimal, terminated
with a newline.
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AWK(1) Utility Commands AWK(1)
//ddeevv//uusseerr Reading this file returns a single record ter-
minated with a newline. The fields are sepa-
rated with blanks. $$11 is the value of the
_g_e_t_u_i_d(2) system call, $$22 is the value of the
_g_e_t_e_u_i_d(2) system call, $$33 is the value of the
_g_e_t_g_i_d(2) system call, and $$44 is the value of
the _g_e_t_e_g_i_d(2) system call. If there are any
additional fields, they are the group IDs
returned by _g_e_t_g_r_o_u_p_s(2). (Multiple groups
may not be supported on all systems.)
//ddeevv//ssttddiinn The standard input.
//ddeevv//ssttddoouutt The standard output.
//ddeevv//ssttddeerrrr The standard error output.
//ddeevv//ffdd//_n The file associated with the open file
descriptor _n.
These are particularly useful for error messages. For
example:
pprriinntt ""YYoouu bblleeww iitt!!"" >> ""//ddeevv//ssttddeerrrr""
whereas you would otherwise have to use
pprriinntt ""YYoouu bblleeww iitt!!"" || ""ccaatt 11>>&&22""
These file names may also be used on the command line to
name data files.
NNuummeerriicc FFuunnccttiioonnss
AWK has the following pre-defined arithmetic functions:
aattaann22((_y,, _x)) returns the arctangent of _y_/_x in radians.
ccooss((_e_x_p_r)) returns the cosine in radians.
eexxpp((_e_x_p_r)) the exponential function.
iinntt((_e_x_p_r)) truncates to integer.
lloogg((_e_x_p_r)) the natural logarithm function.
rraanndd(()) returns a random number between 0 and 1.
ssiinn((_e_x_p_r)) returns the sine in radians.
ssqqrrtt((_e_x_p_r)) the square root function.
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AWK(1) Utility Commands AWK(1)
ssrraanndd((_e_x_p_r)) use _e_x_p_r as a new seed for the random number
generator. If no _e_x_p_r is provided, the time of
day will be used. The return value is the
previous seed for the random number generator.
SSttrriinngg FFuunnccttiioonnss
AWK has the following pre-defined string functions:
ggssuubb((_r,, _s,, _t)) for each substring matching the
regular expression _r in the string
_t, substitute the string _s, and
return the number of substitu-
tions. If _t is not supplied, use
$$00.
iinnddeexx((_s,, _t)) returns the index of the string _t
in the string _s, or 0 if _t is not
present.
lleennggtthh((_s)) returns the length of the string
_s, or the length of $$00 if _s is not
supplied.
mmaattcchh((_s,, _r)) returns the position in _s where
the regular expression _r occurs,
or 0 if _r is not present, and sets
the values of RRSSTTAARRTT and RRLLEENNGGTTHH.
sspplliitt((_s,, _a,, _r)) splits the string _s into the array
_a on the regular expression _r, and
returns the number of fields. If _r
is omitted, FFSS is used.
sspprriinnttff((_f_m_t,, _e_x_p_r_-_l_i_s_t)) prints _e_x_p_r_-_l_i_s_t according to _f_m_t,
and returns the resulting string.
ssuubb((_r,, _s,, _t)) just like ggssuubb(()), but only the
first matching substring is
replaced.
ssuubbssttrr((_s,, _i,, _n)) returns the _n-character substring
of _s starting at _i. If _n is omit-
ted, the rest of _s is used.
ttoolloowweerr((_s_t_r)) returns a copy of the string _s_t_r,
with all the upper-case characters
in _s_t_r translated to their corre-
sponding lower-case counterparts.
Non-alphabetic characters are left
unchanged.
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AWK(1) Utility Commands AWK(1)
ttoouuppppeerr((_s_t_r)) returns a copy of the string _s_t_r,
with all the lower-case characters
in _s_t_r translated to their corre-
sponding upper-case counterparts.
Non-alphabetic characters are left
unchanged.
TTiimmee FFuunnccttiioonnss
Since one of the primary uses of AWK programs is process-
ing log files that contain time stamp information, _g_a_w_k
provides the following two functions for obtaining time
stamps and formatting them.
ssyyssttiimmee(()) returns the current time of day as the number of
seconds since the Epoch (Midnight UTC, January
1, 1970 on POSIX systems).
ssttrrffttiimmee((_f_o_r_m_a_t, _t_i_m_e_s_t_a_m_p))
formats _t_i_m_e_s_t_a_m_p according to the specification
in _f_o_r_m_a_t_. The _t_i_m_e_s_t_a_m_p should be of the same
form as returned by ssyyssttiimmee(()). If _t_i_m_e_s_t_a_m_p is
missing, the current time of day is used. See
the specification for the ssttrrffttiimmee(()) function in
ANSI C for the format conversions that are guar-
anteed to be available. A public-domain version
of _s_t_r_f_t_i_m_e(3) and a man page for it are shipped
with _g_a_w_k; if that version was used to build
_g_a_w_k, then all of the conversions described in
that man page are available to _g_a_w_k_.
SSttrriinngg CCoonnssttaannttss
String constants in AWK are sequences of characters
enclosed between double quotes (""). Within strings, cer-
tain _e_s_c_a_p_e _s_e_q_u_e_n_c_e_s are recognized, as in C. These are:
\\\\ A literal backslash.
\\aa The ``alert'' character; usually the ASCII BEL char-
acter.
\\bb backspace.
\\ff form-feed.
\\nn newline.
\\rr carriage return.
\\tt horizontal tab.
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AWK(1) Utility Commands AWK(1)
\\vv vertical tab.
\\xx_h_e_x _d_i_g_i_t_s
The character represented by the string of hexadeci-
mal digits following the \\xx. As in ANSI C, all fol-
lowing hexadecimal digits are considered part of the
escape sequence. (This feature should tell us some-
thing about language design by committee.) E.g.,
"\x1B" is the ASCII ESC (escape) character.
\\_d_d_d The character represented by the 1-, 2-, or 3-digit
sequence of octal digits. E.g. "\033" is the ASCII
ESC (escape) character.
\\_c The literal character _c.
The escape sequences may also be used inside constant reg-
ular expressions (e.g., //[[ \\tt\\ff\\nn\\rr\\vv]]// matches whitespace
characters).
FFUUNNCCTTIIOONNSS
Functions in AWK are defined as follows:
ffuunnccttiioonn _n_a_m_e((_p_a_r_a_m_e_t_e_r _l_i_s_t)) {{ _s_t_a_t_e_m_e_n_t_s }}
Functions are executed when called from within the action
parts of regular pattern-action statements. Actual parame-
ters supplied in the function call are used to instantiate
the formal parameters declared in the function. Arrays
are passed by reference, other variables are passed by
value.
Since functions were not originally part of the AWK lan-
guage, the provision for local variables is rather clumsy:
they are declared as extra parameters in the parameter
list. The convention is to separate local variables from
real parameters by extra spaces in the parameter list. For
example:
ffuunnccttiioonn ff((pp,, qq,, aa,, bb)) {{ ## aa && bb aarree llooccaall
.......... }}
//aabbcc// {{ ...... ;; ff((11,, 22)) ;; ...... }}
The left parenthesis in a function call is required to
immediately follow the function name, without any inter-
vening white space. This is to avoid a syntactic ambigu-
ity with the concatenation operator. This restriction
does not apply to the built-in functions listed above.
Functions may call each other and may be recursive.
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AWK(1) Utility Commands AWK(1)
Function parameters used as local variables are initial-
ized to the null string and the number zero upon function
invocation.
The word ffuunncc may be used in place of ffuunnccttiioonn.
EEXXAAMMPPLLEESS
Print and sort the login names of all users:
BBEEGGIINN {{ FFSS == ""::"" }}
{{ pprriinntt $$11 || ""ssoorrtt"" }}
Count lines in a file:
{{ nnlliinneess++++ }}
EENNDD {{ pprriinntt nnlliinneess }}
Precede each line by its number in the file:
{{ pprriinntt FFNNRR,, $$00 }}
Concatenate and line number (a variation on a theme):
{{ pprriinntt NNRR,, $$00 }}
SSEEEE AALLSSOO
_e_g_r_e_p(1)
_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, Alfred V. Aho, Brian W.
Kernighan, Peter J. Weinberger, Addison-Wesley, 1988. ISBN
0-201-07981-X.
_T_h_e _G_A_W_K _M_a_n_u_a_l, Edition 0.15, published by the Free Soft-
ware Foundation, 1993.
PPOOSSIIXX CCOOMMPPAATTIIBBIILLIITTYY
A primary goal for _g_a_w_k is compatibility with the POSIX
standard, as well as with the latest version of UNIX _a_w_k.
To this end, _g_a_w_k incorporates the following user visible
features which are not described in the AWK book, but are
part of _a_w_k in System V Release 4, and are in the POSIX
standard.
The --vv option for assigning variables before program exe-
cution starts is new. The book indicates that command
line variable assignment happens when _a_w_k would otherwise
open the argument as a file, which is after the BBEEGGIINN
block is executed. However, in earlier implementations,
when such an assignment appeared before any file names,
the assignment would happen _b_e_f_o_r_e the BBEEGGIINN block was
run. Applications came to depend on this ``feature.''
Free Software Foundation April 15 1993 19
AWK(1) Utility Commands AWK(1)
When _a_w_k was changed to match its documentation, this
option was added to accomodate applications that depended
upon the old behavior. (This feature was agreed upon by
both the AT&T and GNU developers.)
The --WW option for implementation specific features is from
the POSIX standard.
When processing arguments, _g_a_w_k uses the special option
``----'' to signal the end of arguments, and warns about,
but otherwise ignores, undefined options.
The AWK book does not define the return value of ssrraanndd(()).
The System V Release 4 version of UNIX _a_w_k (and the POSIX
standard) has it return the seed it was using, to allow
keeping track of random number sequences. Therefore
ssrraanndd(()) in _g_a_w_k also returns its current seed.
Other new features are: The use of multiple --ff options
(from MKS _a_w_k); the EENNVVIIRROONN array; the \\aa, and \\vv escape
sequences (done originally in _g_a_w_k and fed back into
AT&T's version); the ttoolloowweerr(()) and ttoouuppppeerr(()) built-in
functions (from AT&T); and the ANSI C conversion specifi-
cations in pprriinnttff (done first in AT&T's version).
GGNNUU EEXXTTEENNSSIIOONNSS
_G_a_w_k has some extensions to POSIX _a_w_k. They are described
in this section. All the extensions described here can be
disabled by invoking _g_a_w_k with the --WW ccoommppaatt option.
The following features of _g_a_w_k are not available in POSIX
_a_w_k.
+o The \\xx escape sequence.
+o The ssyyssttiimmee(()) and ssttrrffttiimmee(()) functions.
+o The special file names available for I/O redirec-
tion are not recognized.
+o The AARRGGIINNDD and EERRRRNNOO variables are not special.
+o The IIGGNNOORREECCAASSEE variable and its side-effects are
not available.
+o The FFIIEELLDDWWIIDDTTHHSS variable and fixed width field
splitting.
+o No path search is performed for files named via
the --ff option. Therefore the AAWWKKPPAATTHH environment
variable is not special.
Free Software Foundation April 15 1993 20
AWK(1) Utility Commands AWK(1)
+o The use of nneexxtt ffiillee to abandon processing of the
current input file.
The AWK book does not define the return value of the
cclloossee(()) function. _G_a_w_k's cclloossee(()) returns the value from
_f_c_l_o_s_e(3), or _p_c_l_o_s_e(3), when closing a file or pipe,
respectively.
When _g_a_w_k is invoked with the --WW ccoommppaatt option, if the _f_s
argument to the --FF option is ``t'', then FFSS will be set to
the tab character. Since this is a rather ugly special
case, it is not the default behavior. This behavior also
does not occur if --WW ppoossiixx has been specified.
HHIISSTTOORRIICCAALL FFEEAATTUURREESS
There are two features of historical AWK implementations
that _g_a_w_k supports. First, it is possible to call the
lleennggtthh(()) built-in function not only with no argument, but
even without parentheses! Thus,
aa == lleennggtthh
is the same as either of
aa == lleennggtthh(())
aa == lleennggtthh(($$00))
This feature is marked as ``deprecated'' in the POSIX
standard, and _g_a_w_k will issue a warning about its use if
--WW lliinntt is specified on the command line.
The other feature is the use of the ccoonnttiinnuuee statement
outside the body of a wwhhiillee, ffoorr, or ddoo loop. Traditional
AWK implementations have treated such usage as equivalent
to the nneexxtt statement. _G_a_w_k will support this usage if --WW
ppoossiixx has not been specified.
BBUUGGSS
The --FF option is not necessary given the command line
variable assignment feature; it remains only for backwards
compatibility.
If your system actually has support for //ddeevv//ffdd and the
associated //ddeevv//ssttddiinn, //ddeevv//ssttddoouutt, and //ddeevv//ssttddeerrrr files,
you may get different output from _g_a_w_k than you would get
on a system without those files. When _g_a_w_k interprets
these files internally, it synchronizes output to the
standard output with output to //ddeevv//ssttddoouutt, while on a
system with those files, the output is actually to differ-
ent open files. Caveat Emptor.
Free Software Foundation April 15 1993 21
AWK(1) Utility Commands AWK(1)
VVEERRSSIIOONN IINNFFOORRMMAATTIIOONN
This man page documents _g_a_w_k, version 2.15.
Starting with the 2.15 version of _g_a_w_k, the --cc, --VV, --CC,
--aa, and --ee options of the 2.11 version are no longer rec-
ognized.
AAUUTTHHOORRSS
The original version of UNIX _a_w_k was designed and imple-
mented by Alfred Aho, Peter Weinberger, and Brian
Kernighan of AT&T Bell Labs. Brian Kernighan continues to
maintain and enhance it.
Paul Rubin and Jay Fenlason, of the Free Software Founda-
tion, wrote _g_a_w_k, to be compatible with the original ver-
sion of _a_w_k distributed in Seventh Edition UNIX. John
Woods contributed a number of bug fixes. David Trueman,
with contributions from Arnold Robbins, made _g_a_w_k compati-
ble with the new version of UNIX _a_w_k.
The initial DOS port was done by Conrad Kwok and Scott
Garfinkle. Scott Deifik is the current DOS maintainer.
Pat Rankin did the port to VMS, and Michal Jaegermann did
the port to the Atari ST.
AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS
Brian Kernighan of Bell Labs provided valuable assistance
during testing and debugging. We thank him.
Free Software Foundation April 15 1993 22