.... awk
An input line is normally made up of fields separated by white space, or by 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.
To compensate for inadequate implementation of storage management, the -mr option can be used to set the maximum size of the input record, and the -mf option to set the maximum number of fields.
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 semicolons.
An action is a sequence of statements. A statement can be one of the following:
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 at top
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 \f(CW"\ ", with the usual C escapes recognized within. Expressions take on string or numeric values as appropriate, and are built using the operators + (exponentiation), and concatenation (indicated by white space). The operators ! ++ -- += -= *= /= %= ^= > >= < <= == != ?: 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. Multiple subscripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.
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 statements denote the same open file. The printf statement formats its expression list according to the format (see printf(3)). The built-in function close(expr) closes the file or pipe expr. The built-in function fflush(expr) flushes any buffered output for the file or pipe expr.
The mathematical functions exp, log, sqrt, sin, cos, and atan2 are built in. Other built-in functions:
Patterns are arbitrary Boolean combinations (with ! || &&) of regular expressions and relational expressions. Regular expressions are as in egrep; see grep(1). 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 expression 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 though an occurrence of the second.
A relational expression is one of the following:
expression
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 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 and END do not combine with other patterns.
Variable names with special meanings:
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 function; all other variables are global. Thus local variables may be created by providing excess parameters in the function definition.
Same, with input fields separated by comma and/or blanks and tabs.
{ s += $1 }
END { print "sum is", s, " average is", s/NR }
Add up first column, print sum and average.
BEGIN { # Simulate echo(1)
for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
printf "\n"
exit }
A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Language, Addison-Wesley, 1988. ISBN 0-201-07981-X
The scope rules for variables in functions are a botch; the syntax is worse.