These commands are available on POSIX compliant systems, as well as on traditional Unix based systems. If you are using some other operating system, you still need to be familiar with the ideas of I/O redirection and pipes
Often, these systems
use gawk for their awk implementation!
The `#!' mechanism works on Linux systems, Unix systems derived from Berkeley Unix, System V Release 4, and some System V Release 3 systems.
The
line beginning with `#!' lists the full file name of an interpreter
to be run, and an optional initial command line argument to pass to that
interpreter. The operating system then runs the interpreter with the given
argument and the full argument list of the executed program. The first argument
in the list is the full file name of the awk program. The rest of the
argument list will either be options to awk, or data files,
or both.
The sed utility is a "stream editor."
Its behavior is also defined by the POSIX standard.
The internal representation uses double-precision floating point numbers. If you don't know what that means, then don't worry about it.
Some early implementations of Unix awk initialized
FILENAME to "-", even if there were data files to be
processed. This behavior was incorrect, and should not be relied
upon in your programs.
Computer generated random numbers really are not truly random. They are technically known as "pseudo-random." This means that while the numbers in a sequence appear to be random, you can in fact generate the same sequence of random numbers over and over again.
This consequence was certainly unintended.
As of December 1995, with final approval and publication hopefully sometime in 1996.
Occasionally there are minutes in a year with one or two leap seconds, which is why the seconds can go up to 61.
This is because ANSI C leaves the
behavior of the C version of strftime undefined, and gawk
will use the system's version of strftime if it's there.
Typically, the conversion specifier will either not appear in the
returned string, or it will appear literally.
If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to "internationalize" programs.
Not recommended.
Your version of gawk
may use a directory that is different than `/usr/local/share/awk'; it
will depend upon how gawk was built and installed. The actual
directory will be the value of `$(datadir)' generated when
gawk was configured. You probably don't need to worry about this
though.
Some implementations of awk do not allow you to
execute next from within a function body. Some other work-around
will be necessary if you use such a version.
ASCII
has been extended in many countries to use the values from 128 to 255
for country-specific characters. If your system uses these extensions,
you can simplify _ord_init to simply loop from zero to 255.
This is the Epoch on POSIX systems. It may be different on other systems.
Examine the code in
section Noting Data File Boundaries.
Why must wc use a separate lines variable, instead of using
the value of FNR in endfile?
On older, non-POSIX systems, tr often
does not require that the lists be enclosed in square brackets and quoted.
This is a feature.
This
program was written before gawk acquired the ability to
split each character in a string into separate array elements.
How might this ability simplify the program?
"Real world" is defined as "a program actually used to get something done."
The path may use a directory
other than `/usr/local/share/awk', depending upon how gawk
was built and installed.