4.3BSD-UWisc/man/cat1/awk.1
AWK(1) UNIX Programmer's Manual AWK(1)
NAME
awk - pattern scanning and processing language
SYNOPSIS
awk [ -F_c ] [ prog ] [ file ] ...
DESCRIPTION
_A_w_k 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 pat-
terns may appear literally as _p_r_o_g, or in a file specified
as -f _f_i_l_e.
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 operators +, -, *, /, %, and con-
catenation (indicated by a blank). The C operators ++, --,
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AWK(1) UNIX Programmer's Manual AWK(1)
+=, -=, *=, /=, and %= are also available in expressions.
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 con-
stants are quoted "...".
The _p_r_i_n_t 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 separator, and terminated by the output
record separator. The _p_r_i_n_t_f statement formats its expres-
sion list according to the format (see _p_r_i_n_t_f(3S)).
The built-in function _l_e_n_g_t_h returns the length of its argu-
ment taken as a string, or of the whole line if no argument.
There are also built-in functions _e_x_p, _l_o_g, _s_q_r_t, and _i_n_t.
The last truncates its argument to an integer.
_s_u_b_s_t_r(_s, _m, _n) returns the _n-character substring of _s that
begins at position _m. The function
_s_p_r_i_n_t_f(_f_m_t, _e_x_p_r, _e_x_p_r, ...) formats the expressions
according to the _p_r_i_n_t_f(3S) format given by _f_m_t and returns
the resulting string.
Patterns are arbitrary Boolean combinations (!, ||, &&, and
parentheses) of regular expressions and relational expres-
sions. Regular expressions must be surrounded by slashes
and are as in _e_g_r_e_p. Isolated regular expressions in a pat-
tern 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 combination 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
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AWK(1) UNIX Programmer's Manual AWK(1)
BEGIN { FS = "c" }
or by using the -F_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);
and OFMT, the output format for numbers (default "%.6g").
EXAMPLES
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 $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 }
SEE ALSO
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
BUGS
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 concaten-
ate "" to it.
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