MirBSD manpage: awk(1)
AWK(1) BSD Reference Manual AWK(1)
awk - pattern-directed scanning and processing language
awk [-safe] [-V] [-d[n]] [-F fs] [-v var=value] [prog | -f progfile]
file ...
awk scans each input file for lines that match any of a set of patterns
specified literally in prog or in one or more files specified as -f
progfile. With each pattern there can be an associated action that will
be performed when a line of a file matches the pattern. Each line is
matched against the pattern portion of every pattern-action statement;
the associated action is performed for each matched pattern. The file
name '-' means the standard input. Any file of the form var=value is
treated as an assignment, not a filename, and is executed at the time it
would have been opened if it were a filename.
The options are as follows:
-d[n] Debug mode. Set debug level to n, or 1 if n is not specified. A
value greater than 1 causes awk to dump core on fatal errors.
-F fs Define the input field separator to be the regular expression fs.
-f progfile
Read program code from the specified file progfile instead of
from the command line.
-safe Disable file output (print >, print >>), process creation
(cmd | getline, print , system) and access to the environment
(ENVIRON; see the section on variables below). This is a first
(and not very reliable) approximation to a "safe" version of awk.
-V Print the version number of awk to standard output and exit.
-v var=value
Assign value to variable var before prog is executed; any number
of -v options may be present.
The input is normally made up of input lines (records) separated by new-
lines, or by the value of RS. If RS is null, then any number of blank
lines are used as the record separator, and newlines are used as field
separators (in addition to the value of FS). This is convenient when
working with multi-line records.
An input line is normally made up of fields separated by whitespace, or
by the regular expression FS. The fields are denoted $1, $2, ..., while
$0 refers to the entire line. If FS is null, the input line is split into
one field per character.
Normally, any number of blanks separate fields. In order to set the field
separator to a single blank, use the -F option with a value of '[ ]'. If
a field separator of 't' is specified, awk treats it as if '\t' had been
specified and uses <TAB> as the field separator. In order to use a
literal 't' as the field separator, use the -F option with a value of
'[t]'.
A pattern-action statement has the form
pattern { action }
A missing { action } means print the line; a missing pattern always
matches. Pattern-action statements are separated by newlines or semi-
colons.
Newlines are permitted after a terminating statement or following a comma
(','), an open brace ('{'), a logical AND ('&&'), a logical OR ('||'),
after the 'do' or 'else' keywords, or after the closing parenthesis of an
'if', 'for', or 'while' statement. Additionally, a backslash ('\') can be
used to escape a newline between tokens.
An action is a sequence of statements. A statement can be one of the fol-
lowing:
if (expression) statement [else statement]
while (expression) statement
for (expression; expression; expression) statement
for (var in array) statement
do statement while (expression)
break
continue
{ [statement ...] }
expression # commonly var = expression
print [expression-list] [>expression]
printf format [..., expression-list] [>expression]
return [expression]
next # skip remaining patterns on this input line
nextfile # skip rest of this file, open next, start
delete array[expression] # delete an array element
delete array # delete all elements of array
exit [expression] # exit immediately; status is expression
Statements are terminated by semicolons, newlines or right braces. An
empty expression-list stands for $0. String constants are quoted "", with
the usual C escapes recognized within (see printf(1) for a complete list
of these). Expressions take on string or numeric values as appropriate,
and are built using the operators + - * / % ^ (exponentiation), and con-
catenation (indicated by whitespace). The operators ! ++ -- += -= *= /=
%= ^= > >= < <= == != ?: are also available in expressions. Variables may
be scalars, array elements (denoted x[i]) or fields. Variables are ini-
tialized to the null string. Array subscripts may be any string, not
necessarily numeric; this allows for a form of associative memory. Multi-
ple subscripts such as [i,j,k] are permitted; the constituents are con-
catenated, separated by the value of SUBSEP (see the section on variables
below).
The print statement prints its arguments on the standard output (or on a
file if >file or >>file is present or on a pipe if | cmd is present),
separated by the current output field separator, and terminated by the
output record separator. file and cmd may be literal names or
parenthesized expressions; identical string values in different state-
ments denote the same open file. The printf statement formats its expres-
sion list according to the format (see printf(1)).
Patterns are arbitrary Boolean combinations (with ! || &&) of regular ex-
pressions and relational expressions. awk supports a subset of extended
regular expressions (EREs), excepting repeat counts. See re_format(7) for
more information on regular expressions. Isolated regular expressions in
a pattern apply to the entire line. Regular expressions may also occur in
relational expressions, using the operators ~ and !~. /re/ is a constant
regular expression; any string (constant or variable) may be used as a
regular expression, except in the position of an isolated regular expres-
sion in a pattern.
A pattern may consist of two patterns separated by a comma; in this case,
the action is performed for all lines from an occurrence of the first
pattern through an occurrence of the second.
A relational expression is one of the following:
expression matchop regular-expression
expression relop expression
expression in array-name
(expr, expr, ...) in array-name
where a relop is any of the six relational operators in C, and a matchop
is either ~ (matches) or !~ (does not match). A conditional is an arith-
metic 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 and END do not
combine with other patterns.
Variable names with special meanings:
ARGC Argument count, assignable.
ARGV Argument array, assignable; non-null members are taken as
filenames.
CONVFMT Conversion format when converting numbers (default "%.6g").
ENVIRON Array of environment variables; subscripts are names.
FILENAME The name of the current input file.
FNR Ordinal number of the current record in the current file.
FS Regular expression used to separate fields; also settable by
option -F fs.
NF Number of fields in the current record. $NF can be used to ob-
tain the value of the last field in the current record.
NR Ordinal number of the current record.
OFMT Output format for numbers (default "%.6g").
OFS Output field separator (default blank).
ORS Output record separator (default newline).
RLENGTH The length of the string matched by the match() function.
RS Input record separator (default newline).
RSTART The starting position of the string matched by the match()
function.
SUBSEP Separates multiple subscripts (default 034).
The awk language has a variety of built-in functions: arithmetic, string,
input/output, general, and bit-operation.
Functions may be defined (at the position of a pattern-action statement)
thusly:
function foo(a, b, c) { ...; return x }
Parameters are passed by value if scalar, and by reference if array name;
functions may be called recursively. Parameters are local to the func-
tion; all other variables are global. Thus local variables may be created
by providing excess parameters in the function definition.
atan2(y, x) Return the arctangent of y/x in radians.
cos(x) Return the cosine of x, where x is in radians.
exp(x) Return the exponential of x.
int(x) Return x truncated to an integer value.
log(x) Return the natural logarithm of x.
rand() Return a random number, n, such that 0<=n<1. No further
guarantees are made, especially not on the reproducibility
of the random values, even in the face of srand().
sin(x) Return the sine of x, where x is in radians.
sqrt(x) Return the square root of x.
srand(expr) Sets seed for rand() to expr and returns the previous seed.
If expr is omitted, the time of day is used instead. This
statement is ignored in this implementation.
gsub(r, t, s) The same as sub() except that all occurrences of the
regular expression are replaced. gsub() returns the
number of replacements.
index(s, t) The position in s where the string t occurs, or 0 if it
does not.
length(s) The length of s taken as a string, or of $0 if no argu-
ment is given.
match(s, r) The position in s where the regular expression r occurs,
or 0 if it does not. The variable RSTART is set to the
starting position of the matched string (which is the
same as the returned value) or zero if no match is
found. The variable RLENGTH is set to the length of the
matched string, or -1 if no match is found.
split(s, a, fs) Splits the string s into array elements a[1], a[2], ...,
a[n] and returns n. The separation is done with the reg-
ular expression fs or with the field separator FS if fs
is not given. An empty string as field separator splits
the string into one array element per character.
sprintf(fmt, expr, ...)
The string resulting from formatting expr, ... according
to the printf(1) format fmt.
sub(r, t, s) Substitutes t for the first occurrence of the regular
expression r in the string s. If s is not given, $0 is
used. An ampersand ('&') in t is replaced in string s
with regular expression r. A literal ampersand can be
specified by preceding it with two backslashes ('\\'). A
literal backslash can be specified by preceding it with
another backslash ('\\'). sub() returns the number of
replacements.
substr(s, m, n) Return at most the n-character substring of s that be-
gins at position m counted from 1. If n is omitted, or
if n specifies more characters than are left in the
string, the length of the substring is limited by the
length of s.
tolower(str) Returns a copy of str with all upper-case characters
translated to their corresponding lower-case
equivalents.
toupper(str) Returns a copy of str with all lower-case characters
translated to their corresponding upper-case
equivalents.
close(expr) Closes the file or pipe expr. expr should match the
string that was used to open the file or pipe.
cmd | getline [var] Read a record of input from a stream piped from the
output of cmd. If var is omitted, the variables $0
and NF are set. Otherwise var is set. If the stream
is not open, it is opened. As long as the stream
remains open, subsequent calls will read subsequent
records from the stream. The stream remains open
until explicitly closed with a call to close().
getline returns 1 for a successful input, 0 for end
of file, and -1 for an error.
fflush([expr]) Flushes any buffered output for the file or pipe
expr, or all open files or pipes if expr is omit-
ted. expr should match the string that was used to
open the file or pipe.
getline Sets $0 to the next input record from the current
input file. This form of getline sets the variables
NF, NR, and FNR. getline returns 1 for a successful
input, 0 for end of file, and -1 for an error.
getline var Sets $0 to variable var. This form of getline sets
the variables NR and FNR. getline returns 1 for a
successful input, 0 for end of file, and -1 for an
error.
getline [var] <file Sets $0 to the next record from file. If var is om-
itted, the variables $0 and NF are set. Otherwise
var is set. If file is not open, it is opened. As
long as the stream remains open, subsequent calls
will read subsequent records from file. file
remains open until explicitly closed with a call to
close().
system(cmd) Executes cmd and returns its exit status.
compl(x) Returns the bitwise complement of integer argument x.
and(x, y) Performs a bitwise AND on integer arguments x and y.
or(x, y) Performs a bitwise OR on integer arguments x and y.
xor(x, y) Performs a bitwise Exclusive-OR on integer arguments x and
y.
lshift(x, n) Returns integer argument x shifted by n bits to the left.
rshift(x, n) Returns integer argument x shifted by n bits to the right.
The awk utility exits 0 on success, and >0 if an error occurs.
But note that the exit expression can modify the exit status.
Print lines longer than 72 characters:
length($0) > 72
Print first two fields in opposite order:
{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and tabs:
BEGIN { FS = ",[ \t]*|[ \t]+" }
{ print $2, $1 }
Add up first column, print sum and average:
{ s += $1 }
END { print "sum is", s, " average is", s/NR }
Print all lines between start/stop pairs:
/start/, /stop/
Simulate echo(1):
BEGIN { # Simulate echo(1)
for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
printf "\n"
exit }
Print an error message to standard error:
{ print "error!" > "/dev/stderr" }
lex(1), printf(1), sed(1), re_format(7), script(7)
A. V. Aho, B. W. Kernighan, and P. J. Weinberger, The AWK Programming
Language, Addison-Wesley, 1988, ISBN 0-201-07981-X.
The awk utility is compliant with the IEEE Std 1003.1-2008 ("POSIX.1")
specification, except awk lacks support for repeat counts ("{n,m}") in
regular expressions.
The flags [-dV] and [-safe], as well as the commands fflush, compl, and,
or, xor, lshift, rshift, are extensions to that specification.
An awk utility appeared in Version 7 AT&T UNIX.
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 "" to it.
The scope rules for variables in functions are a botch; the syntax is
worse.
MirBSD #10-current August 17, 2021 5