AWK(1) 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 associ‐ ated 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 -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 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 sub‐ scripts may be any string, not necessarily numeric; this allows for a form of associative memory. String constants 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 sep‐ arator, and terminated by the output record separator. The _p_r_i_n_t_f statement formats its expression 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 argument 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 sub‐ string 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 parenthe‐ ses) of regular expressions and relational expressions. Regular expressions must be surrounded by slashes and are as in _e_g_r_e_p. Iso‐ lated regular expressions in a pattern apply to the entire line. Regu‐ lar 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 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 concatenate "" to it. 7th Edition April 29, 1985 AWK(1)