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(gawk.info)Concatenation

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String Concatenation
====================

     It seemed like a good idea at the time.
     Brian Kernighan

   There is only one string operation: concatenation.  It does not have
a specific operator to represent it.  Instead, concatenation is
performed by writing expressions next to one another, with no operator.
For example:

     $ awk '{ print "Field number one: " $1 }' BBS-list
     -| Field number one: aardvark
     -| Field number one: alpo-net
     ...

   Without the space in the string constant after the `:', the line
runs together.  For example:

     $ awk '{ print "Field number one:" $1 }' BBS-list
     -| Field number one:aardvark
     -| Field number one:alpo-net
     ...

   Because string concatenation does not have an explicit operator, it
is often necessary to insure that it happens at the right time by using
parentheses to enclose the items to concatenate.  For example, the
following code fragment does not concatenate `file' and `name' as you
might expect:

     file = "file"
     name = "name"
     print "something meaningful" > file name

It is necessary to use the following:

     print "something meaningful" > (file name)

   Parentheses should be used around concatenation in all but the most
common contexts, such as on the righthand side of `='.  Be careful
about the kinds of expressions used in string concatenation.  In
particular, the order of evaluation of expressions used for
concatenation is undefined in the `awk' language.  Consider this
example:

     BEGIN {
         a = "don't"
         print (a " " (a = "panic"))
     }

It is not defined whether the assignment to `a' happens before or after
the value of `a' is retrieved for producing the concatenated value.
The result could be either `don't panic', or `panic panic'.  The
precedence of concatenation, when mixed with other operators, is often
counter-intuitive.  Consider this example:

     $ awk 'BEGIN { print -12 " " -24 }'
     -| -12-24

   This "obviously" is concatenating -12, a space, and -24.  But where
did the space disappear to?  The answer lies in the combination of
operator precedences and `awk''s automatic conversion rules.  To get
the desired result, write the program in the following manner:

     $ awk 'BEGIN { print -12 " " (-24) }'
     -| -12 -24

   This forces `awk' to treat the `-' on the `-24' as unary.
Otherwise, it's parsed as follows:

         -12 (`" "' - 24)
     => -12 (0 - 24)
     => -12 (-24)
     => -12-24

   As mentioned earlier, when doing concatenation, _parenthesize_.
Otherwise, you're never quite sure what you'll get.