Compatibility and Compliance

Date and time functions

The date and time functions (mktime(), strftime()) follow the Java platform's time zone data and calendar rules rather than the C library's, which differs from gawk in a few edge cases:

• ENVIRON["TZ"] accepts the zone IDs Java understands: Olson names such as Europe/Paris (optionally with a POSIX : prefix) and Java's custom GMT+3 IDs with Java's sign convention (GMT+3 is UTC+03:00, where POSIX would read UTC-03:00). POSIX TZ rule specifications such as XXX3 or CET-1CEST,M3.5.0,M10.5.0/3 are not parsed; unknown zones fall back to GMT. An explicitly empty TZ selects UTC, as in POSIX.
• An ambiguous wall time during a DST fall-back resolves to its standard-time occurrence; the explicit DST field of mktime() still selects either occurrence.
• A positive mktime() DST hint applies the zone's current daylight adjustment; zones without daylight saving time ignore the hint.
• strftime()'s %Z prints the zone's current designation (the JDK's time zone data records historical offsets and DST rules, but not historical zone names), and timestamps before the common era use the JDK's year numbering rather than astronomical (negative) years.

Range patterns

Range patterns (begpat, endpat) evaluate their two conditions lazily, as POSIX requires: the start condition is evaluated only while outside the range, and the end condition only once the range has started — including on the very record that starts it, so a range can begin and end on the same record. Conditions with side effects, such as a++ == 2, a++ == 5, therefore behave exactly as in gawk and One True Awk: each condition's side effects run only on the records where that condition is actually tested.

Where Jawk follows gawk

Jawk follows gawk in several places where gawk departs from historical AWK:

• A regexp literal used as an ordinary expression evaluates as $0 ~ /re/, per POSIX; x = /re/ assigns 0 or 1, not the pattern text.
• Typed regexp literals (@/re/) are accepted; --posix rejects them.
• IGNORECASE is a built-in special variable managed by the runtime, like FS or RS: a truthy value makes regexp matching, field and split() separators, string comparisons, index(), and gawk array sorting case-insensitive.
• Because the gawk compatibility extension^[7] is enabled by default, gensub, typeof, isarray, asort, asorti, mkbool, patsplit, strtonum, systime, mktime, strftime, bindtextdomain, dcgettext, and dcngettext are function names and can no longer be used as variables. Load an explicit extension list without GawkExtension to reclaim those identifiers.
• Calling a user-defined function with more arguments than it declares is accepted: the extra expressions are evaluated and discarded, and a gawk-style warning is printed to stderr.
• Assigning a scalar value to an array element (a[1] = z) types that element as a scalar; later using it as a subarray (a[1][2] = 3) is a runtime error, exactly as in gawk.
• print and printf resolve the leading-parenthesis ambiguity as gawk does: print (a, b) prints the parenthesized group as the whole argument list (which is how print (a, b) > "file" disambiguates a redirection from a comparison), while a single parenthesized expression followed by a comma continues the output list, as in print (i==0), (i==""), and a group followed by in is a membership key, as in print (1,2) in a. A comma group followed by more arguments, such as print (1,2), 3, is a syntax error. More generally, outside of a print/printf argument list, a parenthesized expression list such as (i, j) is a grouping, not an expression, and is only valid immediately before in, as in ((i, j) in array).