4.3BSD-Reno/share/man/cat1/awk.0
AWK(1) UNIX Reference Manual AWK(1)
NNAAMMEE
aawwkk - pattern scanning and processing language
SSYYNNOOPPSSIISS
aawwkk [--FF_c] [--ff _p_r_o_g__f_i_l_e] [_p_r_o_g] [_f_i_l_e ...]
DDEESSCCRRIIPPTTIIOONN
AAwwkk scans each input _f_i_l_e for lines that match any of a set of patterns
specified in _p_r_o_g. With each pattern in _p_r_o_g there can be an associated
action that will be performed when a line of a _f_i_l_e matches the pattern.
The set of patterns may appear literally as _p_r_o_g or in a file specified
as --ff _f_i_l_e.
--FF_c Specify a field separator of _c.
--ff Use _p_r_o_g__f_i_l_e as an input _p_r_o_g (an awk script).
Files are read in order; if there are no files, the standard input is
read. The file name `--' means the standard input. Each line is matched
against the pattern portion of every pattern-action statement; the
associated action is performed for each matched pattern.
An input line is made up of fields separated by white space. (This
default can be changed by using FS, _v_i_d_e _i_n_f_r_a.) The fields are denoted
$1, $2, ... ; $0 refers to the entire line.
A pattern-action statement has the form
pattern {action}
A missing { action } means print the line; a missing pattern always
matches.
An action is a sequence of statements. A statement can be one of the
following:
if ( conditional ) statement [ else statement ]
while ( conditional ) statement
for ( expression ; conditional ; expression ) statement
break
continue
{ [ statement ] ... }
variable = expression
print [ expression-list ] [ >expression ]
printf format [, expression-list ] [ >expression ]
next # skip remaining patterns on this input line
exit # skip the rest of the input
Statements are terminated by semicolons, newlines or right braces. An
empty expression-list stands for the whole line. Expressions take on
string or numeric values as appropriate, and are built using the opera-
tors +, -, *, /, %, and concatenation (indicated by a blank). The C
operators ++, --, +=, -=, *=, /=, and %= are also available in expres-
sions. Variables may be scalars, array elements (denoted x[i]) or
fields. Variables are initialized to the null string. Array subscripts
may be any string, not necessarily numeric; this allows for a form of
associative memory. String constants are quoted "...".
The pprriinntt statement prints its arguments on the standard output (or on a
file if >_f_i_l_e is present), separated by the current output field separa-
tor, and terminated by the output record separator. The pprriinnttff statement
formats its expression list according to the format (see printf(3)).
The built-in function lleennggtthh returns the length of its argument taken as
a string, or of the whole line if no argument. There are also built-in
functions eexxpp, lloogg, ssqqrrtt and iinntt. The last truncates its argument to an
integer. The function ssuubbssttrr(_s, _m, _n) returns the _n-character substring
of _s that begins at position _m. The sspprriinnttff(_f_m_t, _e_x_p_r, _e_x_p_r, ...) func-
tion formats the expressions according to the printf(3) format given by
_f_m_t and returns the resulting string.
Patterns are arbitrary Boolean combinations (!, ||, &&, and parentheses)
of regular expressions and relational expressions. Regular expressions
must be surrounded by slashes and are as in egrep(1). Isolated regular
expressions in a pattern apply to the entire line. Regular expressions
may also occur in relational expressions.
A pattern may consist of two patterns separated by a comma; in this case,
the action is performed for all lines between an occurrence of the first
pattern and the next occurrence of the second.
A relational expression is one of the following:
expression matchop regular-expression
expression relop expression
where a relop is any of the six relational operators in C, and a matchop
is either ~ (for contains) or !~ (for does not contain). A conditional
is an arithmetic expression, a relational expression, or a Boolean combi-
nation of these.
The special patterns BEGIN and END may be used to capture control before
the first input line is read and after the last. BEGIN must be the first
pattern, END the last.
A single character _c may be used to separate the fields by starting the
program with
BEGIN { FS = c }
or by using the --FF_c option.
Other variable names with special meanings include
NF the number of fields in the current record;
NR the ordinal number of the current record;
FILENAME the name of the current input file;
OFS the output field separator (default blank);
ORS the output record separator (default newline);
OFMT the output format for numbers (default "%.6g").
EEXXAAMMPPLLEESS
Print lines longer than 72 characters:
length > 72
Print first two fields in opposite order:
{ print $2, $1 }
Add up first column, print sum and average:
{ s += $1 }
END { print "sum is", s, " average is", s/NR }
Print fields in reverse order:
{ for (i = NF; i > 0; --i)
Print all lines between start/stop pairs:
/start/, /stop/
Print all lines whose first field is different from previous one:
$1 != prev { print; prev = $1 }
SSEEEE AALLSSOO
lex(1), sed(1)
A. V. Aho, B. W. Kernighan, P. J. Weinberger, _A_w_k - _a _p_a_t_t_e_r_n _s_c_a_n_n_i_n_g
_a_n_d _p_r_o_c_e_s_s_i_n_g _l_a_n_g_u_a_g_e
HHIISSTTOORRYY
AAwwkk appeared in Version 7 AT&T UNIX. A much improved and true to the
book version of aawwkk appeared in the AT&T Toolchest in the late 1980's.
The version of aawwkk this manual page describes is a derivative of the ori-
ginal and not the Toolchest version.
BBUUGGSS
There are no explicit conversions between numbers and strings. To force
an expression to be treated as a number add 0 to it; to force it to be
treated as a string concatenate "" (an empty string) to it.