awk(1) awk(1) NAME awk, nawk, pawk - pattern scanning and processing language SYNOPSIS awk [-F re] [-v var=value] ['prog'] [file. . .] awk [-F re] [-v var=value] [-f progfile] [file. . .] DESCRIPTION NOTE: This version of awk has some incompatibilities with previous versions. See the COMPATIBILITY ISSUES section below for more detail. awk and nawk use the old regexp() and compile() regular expression routines. When the environment variable _XPG is equal to 1 (one), pawk is exec'ed which uses the newer regcomp() and regexec() routines which implement the Extended Regular Expression package. awk scans each input file for lines that match any of a set of patterns specified in prog. The prog string must be enclosed in single quotes (') to protect it from the shell. Patterns are arbitrary Boolean combinations of regular expressions and relational expressions. For each pattern in prog there may be an associated action performed when a line of a file matches the pattern. The set of pattern-action statements may appear literally as prog or in a file specified with the -f progfile option. Input files are read in order; if there are no files, the standard input is read. The file name - means the standard input. awk processes supplementary code set characters in pattern-action statements and comments, and recognizes supplementary code set characters as field separators (see below) according to the locale specified in the LC_CTYPE environment variable [see LANG on environ(5)]. In regular expressions, pattern searches are performed on characters, not bytes, as described on ed(1). Each input line is matched against the pattern portion of every pattern- action statement; the associated action is performed for each matched pattern. Any file of the form var=value is treated as an assignment, not a filename. If the environment variable _XPG is equal to 1 (one), each such assignment is executed at the time it would have been opened if it were a filename. If the environment variable _XPG is not set, all assignments that appear before the first actual file are processed as if each was preceded by the -v opton. The option -v followed by var=value is an assignment to be done before prog is executed; any number of -v options may be present. An input line is normally made up of fields separated by white space. (This default can be changed by using the FS built-in variable or the -F re option.) The fields are denoted $1, $2, ...; $0 refers to the entire line. A pattern-action statement has the form: pattern { action } Either pattern or action may be omitted. If there is no action with a pattern, the matching line is printed. If there is no pattern with an action, the action is performed on every input line. Pattern-action statements are separated by newlines or semicolons. As noted, patterns are arbitrary Boolean combinations ( !, ||, &&, and parentheses) of relational expressions and regular expressions. A relational expression is one of the following: expression relop expression expression matchop regular_expression expression in array-name (expression,expression, ... ) in array-name where a relop is any of the six relational operators in C, and a matchop is either ~ (contains) or !~ (does not contain). An expression is an arithmetic expression, a relational expression, the special expression var in array or a Boolean combination of these. Regular expressions are as in egrep(1). In patterns they must be surrounded by slashes. 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 pattern. The special patterns BEGIN and END may be used to capture control before the first input line has been read and after the last input line has been read respectively. These keywords do not combine with any other patterns. A regular expression may be used to separate fields by using the -F re option or by assigning the expression to the built-in variable FS. The default is to ignore leading blanks and to separate fields by blanks and/or tab characters. However, if FS is assigned a value, leading blanks are no longer ignored. Other built-in variables include: ARGC command line argument count ARGV command line argument array. Note: The value of ARGV[0] depends on the environment variable _XPG. See NOTES and COMPATIBILITY ISSUES section. ENVIRON array of environment variables; subscripts are names FILENAME name of the current input file FNR ordinal number of the current record in the current file FS input field separator regular expression (default blank and tab) NF number of fields 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 new-line) RS input record separator (default new-line) SUBSEP separates multiple subscripts (default is 034) The field separators specified with the -F option or with the variables OFS, ORS, and FS may be supplementary code set characters. An action is a sequence of statements. A statement may be one of the following: if ( expression ) statement [ else statement ] while ( expression ) statement do statement while ( expression ) for ( expression ; expression ; expression ) statement for ( var in array ) statement delete array[subscript] #delete an array element break continue { [ statement ] ... } expression # commonly variable = expression print [ expression-list ] [ >expression ] printf format [ , expression-list ] [ >expression ] next # skip remaining patterns on this input line exit [expr] # skip the rest of the input; exit status is expr return [expr] Statements are terminated by semicolons, new-lines, or right braces. An empty expression-list stands for the whole input line. Expressions take on string or numeric values as appropriate, and are built using the operators +, -, *, /, %, ^ and concatenation (indicated by a blank). 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 or zero. 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. String constants are quoted (""), with the usual C escapes recognized within. A comment consists of any characters beginning with the number sign character and terminated by, but excluding the next occurrence of, a newline character. Comments will have no effect, except to delimit statements. The print statement prints its arguments on the standard output, or on a file if >expression is present, or on a pipe if | cmd is present. The arguments are separated by the current output field separator and terminated by the output record separator. The printf statement formats its expression list according to the format (see printf(3S)). The built-in function close(expr) closes the file or pipe expr. The mathematical functions: atan2, cos, exp, log, sin, sqrt, are built- in. Other built-in functions include: gsub(for, repl, in) behaves like sub (see below), except that it replaces successive occurrences of the regular expression (like the ed global substitute command). index(s, t) returns the position in string s where string t first occurs, or 0 if it does not occur at all. int truncates to an integer value. length(s) returns the length in bytes of its argument taken as a string, or of the whole line if there is no argument. match(s, re) returns the position in string s where the regular expression re occurs, or 0 if it does not occur at all. RSTART is set to the starting position (which is the same as the returned value), and RLENGTH is set to the length of the matched string. rand random number on (0, 1). 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 regular expression fs or with the field separator FS if fs is not given. srand sets the seed for rand sprintf(fmt, expr, expr,...) formats the expressions according to the printf(3S) format given by fmt and returns the resulting string. sub(for, repl, in) substitutes the string repl in place of the first instance of the regular expression for in string in and returns the number of substitutions. If in is omitted, awk substitutes in the current record ($0). substr(s, m, n) returns the n-byte substring of s that begins at position m. tolower(s) converts all upper-case alphabetic characters in string s to lower-case. Numbers and other characters are not affected. toupper(s) converts all lower-case alphabetic characters in string s to upper-case. Numbers and other characters are not affected. The input/output built-in functions are: close(filename) closes the file or pipe named filename. cmd | getline pipes the output of cmd into getline; each successive call to getline returns the next line of output from cmd. getline sets $0 to the next input record from the current input file. getline <file sets $0 to the next record from file. getline x sets variable x instead. getline x <file sets x from the next record of file. system(cmd) executes cmd and returns its exit status. All forms of getline return 1 for successful input, 0 for end of file, and -1 for an error. awk also provides user-defined functions. Such functions may be defined (in the pattern position of a pattern-action statement) as function name(args,...) { stmts } Function arguments are passed by value if scalar and by reference if array name. Argument names are local to the function; all other variable names are global. Function calls may be nested and functions may be recursive. The return statement may be used to return a value. EXAMPLES Print lines longer than 72 characters: length > 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 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 } Simulate echo(1): BEGIN { for (i = 1; i < ARGC; i++) printf "%s", ARGV[i] printf "\n" exit } Print a file, filling in page numbers starting at 5: /Page/ { $2 = n++; } { print } Assuming this program is in a file named prog, the following command line prints the file input numbering its pages starting at 5: awk -f prog n=5 input. FILES /usr/lib/locale/locale/LC_MESSAGES/uxawk language-specific message file (see LANG on environ(5)) SEE ALSO oawk(1), egrep(1), grep(1), lex(1), perl(1), sed(1), printf(3S) A. V. Aho, B. W. Kernighan, P. J. Weinberger, The awk Programming Language Addison-Wesley, 1988 NOTES and COMPATIBILITY ISSUES awk is a newer version that provides capabilities unavailable in previous versions. See oawk(1) for the older version. Input white space is not preserved on output if fields are involved. 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 the null string ("") to it. The following regular expressions are no longer accepted: /[]/ /[^]/ /[\]]/ When the environment variable _XPG is equal to 1 (one), pawk returns the command in ARGV[0] untouched. Otherwise, the default is to return the command name stripped of the leading path. Page 7