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An awk pattern can be any expression involving comparisons between strings of characters or numbers. awk has six relational operators, and two extended regular expression matching operators, ~ (tilde) and !~, which are discussed in the next section, for making comparisons. ``awk comparison operators'' lists these operators and their meanings.
awk comparison operators
| Operator | Meaning |
|---|---|
| < | less than |
| <= | less than or equal to |
| == | equal to |
| != | not equal to |
| >= | greater than or equal to |
| > | greater than |
| ~ | matches |
| !~ | does not match |
In a comparison, if both operands are numeric, a numeric comparison is made; otherwise, the operands are compared as strings. (Every value might be either a number or a string; usually awk can tell what is intended. ``Number or string?'' contains more information about this.) Thus, the pattern $3>100 selects lines where the third field exceeds 100, and the program
$1 >= "S"selects lines that begin with the letters S through Z, namely,
USSR 8650 262 Asia USA 3615 219 North America Sudan 968 19 AfricaIn the absence of any other information, awk treats fields as strings, so the program
$1 == $4compares the first and fourth fields as strings of characters, and with the file countries as input, prints the single line for which this test succeeds:
Australia 2968 14 AustraliaIf both fields appear to be numbers, the comparisons are done numerically.