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https://sourceforge.net/projects/gnuwin32/forums/forum/74807/topic/4550522
By: raysatiro
Reggie what you first need to understand is how your command line arguments
will be seen by a gcc compiled C program after the command line is parsed. I
wrote a very simple program to demonstrate this. These examples were made using
the windows command interpreter.
[code]
C:\Temp>getargs "{if (substr($1,1,3) == "123") print $0}"
argv[ 0 ]: getargs
argv[ 1 ]: {if (substr($1,1,3) == 123) print $0}
C:\Temp>getargs "{if (substr($1,1,3) == \"123\") print $0}"
argv[ 0 ]: getargs
argv[ 1 ]: {if (substr($1,1,3) == "123") print $0}
C:\Temp>getargs "{if (substr($1,1,3) == "Sun") print $0}"
argv[ 0 ]: getargs
argv[ 1 ]: {if (substr($1,1,3) == Sun) print $0}
C:\Temp>getargs "{if (substr($1,1,3) == \"Sun\") print $0}"
argv[ 0 ]: getargs
argv[ 1 ]: {if (substr($1,1,3) == "Sun") print $0}
C:\Temp>getargs "apple "orange" pear"
argv[ 0 ]: getargs
argv[ 1 ]: apple orange pear
C:\Temp>getargs "apple " orange " pear"
argv[ 0 ]: getargs
argv[ 1 ]: apple
argv[ 2 ]: orange
argv[ 3 ]: pear
C:\Temp>getargs "apple \" orange \" pear"
argv[ 0 ]: getargs
argv[ 1 ]: apple " orange " pear
C:\Temp>getargs "apple""orange"
argv[ 0 ]: getargs
argv[ 1 ]: apple"orange
C:\Temp>getargs "apple "" orange"
argv[ 0 ]: getargs
argv[ 1 ]: apple "
argv[ 2 ]: orange
C:\Temp>getargs "apple"
argv[ 0 ]: getargs
argv[ 1 ]: apple
C:\Temp>getargs \"apple\"
argv[ 0 ]: getargs
argv[ 1 ]: "apple"
[/code]
Arguments are separated by spaces and each argument can be quoted. If an
argument
contains spaces it must be quoted. If an argument contains special characters
in most cases it should/must be quoted. If an argument contains quotes in the
argument in most cases you would want to escape them. There is also
"apple""orange"
parsed as one argument apple"orange . But that is undocumented. If you want
a more thorough understanding of command line parsing go here:
http://www.autohotkey.net/~deleyd/parameters/parameters.htm#WIN
Now as to your question. You can see above that what is happening is while in
your first command you may have intended to compare to a numeric string of
"123" you were actually comparing a numeric of 123 because you didn't escape
the quotes. gawk's type comparison rules, which are the same as POSIX's, allow
that. It gets kind of complicated but basically it's okay to compare what you
get from substr() to a numeric.
Also, while you intended to compare to a string of "Sun" you were actually
comparing
to a variable named Sun because you didn't escape the quotes. Unless the
unquoted
argument in that if statement is a numeric (+2 or 234 etc.) gawk interprets
it as a variable name. In this case an undefined variable, because there is
no variable named Sun... unless you define it, and why would you do that except
to make things really confusing!
If you feel up to it review gawk's documentation on String Type Versus Numeric
Type:
http://www.gnu.org/software/gawk/manual/html_node/Variable-Typing.html#Variable-
Typing
One of the most confusing issues for gnuwin32 users reading GNU documentation
is that in many cases it assumes a POSIX compliant shell when it gives usage
examples. The windows command interpreter (what most users use) is certainly
not a POSIX compliant shell. So the examples in the link above you won't be
able to run in a windows command interpreter due to the way they're quoted.
You must use double quotes. So take this example:
[code]echo ' +3.14' | gawk '{ print $1 == "+3.14" }'[/code]
In the windows command interpreter you must do it like this:
[code]c:\gnuwin32\bin\echo " +3.14" | gawk "{ print $1 == \"+3.14\" }"[/code]
Although I focused on the windows command interpreter there are POSIX shells
for windows that you can use instead of the command interpreter.
If you want POSIX compliance Microsoft offers that for certain versions
of windows:
http://en.wikipedia.org/wiki/Windows_Services_for_UNIX
Personally I alternate between the POSIX bash shell that came with my MSYS
installation and the windows command interpreter. I don't use SFU.
As your gawk code becomes more complex it will be easier to just move it to
a script file where you won't have any of these problems, POSIX shell or not.
gawk -f yourscript in.txt > out.txt
The program getargs and its source is available here:
https://sourceforge.net/projects/getgnuwin32/files/getgnuwin32/other/getargs/
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