1#ident "%Z%%M% %I% %E% SMI" 2 3CDDL HEADER START 4 5The contents of this file are subject to the terms of the 6Common Development and Distribution License, Version 1.0 only 7(the "License"). You may not use this file except in compliance 8with the License. 9 10You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 11or http://www.opensolaris.org/os/licensing. 12See the License for the specific language governing permissions 13and limitations under the License. 14 15When distributing Covered Code, include this CDDL HEADER in each 16file and include the License file at usr/src/OPENSOLARIS.LICENSE. 17If applicable, add the following below this CDDL HEADER, with the 18fields enclosed by brackets "[]" replaced with your own identifying 19information: Portions Copyright [yyyy] [name of copyright owner] 20 21CDDL HEADER END 22 23Nov 30, 1979: 24 25Awk has been modified yet again, in an attempt to make 26its behavior more rational and predictable in the areas 27of initialization, comparison, and type coercion. 28Herewith what we believe the current truth to be: 29 301. Each variable and field can potentially be a string 31or a number or both at any time. 32When a variable is set by the assignment 33 v = expr 34its type is set to that of expr. (This includes +=, ++, etc.) 35An arithmetic expression is of type number, a 36concatenation is of type string, and so on. 37 38If the assignment is a simple copy, as in 39 v1 = v2 40then the type of v1 becomes that of v2. 41 422. In comparisons, if both operands are numeric, 43the comparison is made numerically. Otherwise, 44operands are coerced to string if necessary, and 45the comparison is made on strings. 46 473. The type of any expression can be coerced to 48numeric by subterfuges (kludges?) such as 49 expr + 0 50and to string by 51 expr "" 52(i.e., concatenation with a null string). 53 544. Uninitialized variables have the numeric value 550 and the string value "". Accordingly, if x is 56uninitialized, 57 if (x) ... 58is false, and 59 if (!x) ... 60 if (x == 0) ... 61 if (x == "") ... 62are all true. But note that 63 if (x == "0") ... 64is false. 65 665. The type of a field is determined by context 67when possible; for example, 68 $1++ 69clearly implies that $1 is to be numeric, and 70 $1 = $1 "," $2 71implies that $1 and $2 are both to be strings. 72Coercion will be done as needed. 73 74In contexts where types cannot be reliably determined, e.g., 75 if ($1 == $2) ... 76the type of each field is determined on input by 77inspection. All fields are strings; in addition, 78each field that contains only a number (in the 79sense of Fortran, say) is also considered numeric. 80This ensures (for better or worse) that the test 81 if ($1 == $2) ... 82will succeed on the inputs 83 0 0.0 84 100 1e2 85 +100 100 86 1e-3 1e-3 87and fail on the inputs 88 (null) 0 89 (null) 0.0 90 2E-518 6E-427 91as we believe it should. 92 93Fields which are explicitly null have the string 94value ""; they are not numeric. 95Non-existent fields (i.e., fields past NF) are 96treated this way too. 97 98As it is for fields, so it is for array elements 99created by split(...). 100 1016. There is no warranty of merchantability nor any warranty 102of fitness for a particular purpose nor any other warranty, 103either express or implied, as to the accuracy of the 104enclosed materials or as to their suitability for any 105particular purpose. Accordingly, the AWK Development 106Task Force assumes no responsibility for their use by the 107recipient. Further, the Task Force assumes no obligation 108to furnish any assistance of any kind whatsoever, or to 109furnish any additional information or documentation. 110