gawk: Strings And Numbers
6.1.4.1 How 'awk' Converts Between Strings and Numbers
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Strings are converted to numbers and numbers are converted to strings,
if the context of the 'awk' program demands it. For example, if the
value of either 'foo' or 'bar' in the expression 'foo + bar' happens to
be a string, it is converted to a number before the addition is
performed. If numeric values appear in string concatenation, they are
converted to strings. Consider the following:
two = 2; three = 3
print (two three) + 4
This prints the (numeric) value 27. The numeric values of the variables
'two' and 'three' are converted to strings and concatenated together.
The resulting string is converted back to the number 23, to which 4 is
then added.
If, for some reason, you need to force a number to be converted to a
string, concatenate that number with the empty string, '""'. To force a
string to be converted to a number, add zero to that string. A string
is converted to a number by interpreting any numeric prefix of the
string as numerals: '"2.5"' converts to 2.5, '"1e3"' converts to 1,000,
and '"25fix"' has a numeric value of 25. Strings that can't be
interpreted as valid numbers convert to zero.
The exact manner in which numbers are converted into strings is
controlled by the 'awk' predefined variable 'CONVFMT' (
Built-in
Variables). Numbers are converted using the 'sprintf()' function with
'CONVFMT' as the format specifier (String Functions).
'CONVFMT''s default value is '"%.6g"', which creates a value with at
most six significant digits. For some applications, you might want to
change it to specify more precision. On most modern machines, 17 digits
is usually enough to capture a floating-point number's value exactly.(1)
Strange results can occur if you set 'CONVFMT' to a string that
doesn't tell 'sprintf()' how to format floating-point numbers in a
useful way. For example, if you forget the '%' in the format, 'awk'
converts all numbers to the same constant string.
As a special case, if a number is an integer, then the result of
converting it to a string is _always_ an integer, no matter what the
value of 'CONVFMT' may be. Given the following code fragment:
CONVFMT = "%2.2f"
a = 12
b = a ""
'b' has the value '"12"', not '"12.00"'. (d.c.)
Pre-POSIX 'awk' Used 'OFMT' for String Conversion
Prior to the POSIX standard, 'awk' used the value of 'OFMT' for
converting numbers to strings. 'OFMT' specifies the output format to
use when printing numbers with 'print'. 'CONVFMT' was introduced in
order to separate the semantics of conversion from the semantics of
printing. Both 'CONVFMT' and 'OFMT' have the same default value:
'"%.6g"'. In the vast majority of cases, old 'awk' programs do not
change their behavior. Print for more information on the
'print' statement.
---------- Footnotes ----------
(1) Pathological cases can require up to 752 digits (!), but we doubt
that you need to worry about this.
Info Catalog
gawk: Conversion
gawk: Locale influences conversions