请问如何将环境变量带入awk的判断里去？

zhangjoto

我用ipcs查共享内存，找到某个用户所创建的共享内存后做某个动作，
但是不知道怎么把环境变量放在awk的if语句里，(不用grep，不准确)

请问各位有什么方法？
SCO UNIX +KSH

admirer

比如在awk中引用PATH可以这样做：

echo | awk '{PATH="'"$PATH"'";print PATH}'

yuwang007

还可以用-v



A=3
echo haha | awk -v v1=$A  ' { print v1 }'

panlm

14. How can I access shell or environment variables in an awk script?

14.0 shells

the examples using quoting are intended for use with any standard
(sh-compatible-quoting) Unix shell.  as with all complex quoting,
all these examples become much easier to work with (or under DOS
and MS-Windows, less impossible) when put in a file and invoked with
`awk -f filename.awk' instead.

non-sh-compatible shells will require different quoting.  if you're
not even using Unix (or a ported Unix shell), just ignore the whole
section on quoting.

14.1 Environment variables in general

Answer 1:  on Unix, use "alternate quoting", e.g.

        awk -F: '$1 ~ /'"$USER"'/ {print $5}' /etc/passwd
                ^^^^^^^^*******^^^^^^^^^^^^^^

        any standard Unix shell will send the underlined part as one
        long argument (with embedded spaces) to awk, for instance:

        $1 ~ /bwk/ {print $5}

        Note that there may not be any spaces between the quoted
        parts.  Otherwise, you wouldn't end up a single, long script
        argument, because Unix shells break arguments on spaces
        (unless they are `escaped' with `\', or in '' or "", as the
        above example shows).

Answer 2:  RTFM to see if and how your awk supports variable definitions
           on the command line, e.g.,

        awk -F: -v name="$USER" '$1 ~ name {print $5}' /etc/passwd

Answer 3:  RTFM if your awk can access enviroment vars.  Then perhaps

        awk -F: '$1 ~ ENVIRON["USER"] {print $5}' /etc/passwd

        Always remember for your /bin/sh scripts that it's easy to put
        things into the environment for a single command run:

        name=felix age=56 awk '... ENVIRON["name"] .....'

        this also works with ksh and some other shells.

The first approach is extremely portable, but doesn't work with
awk "-f" script files.  In that case, it's better to use a shell
script and stretch a long awk command argument in '...' across
multiple lines if need be.

Also note: /bin/csh requires a \ before an embedded newline, /bin/sh not.


14.2 Unix Shell Quoting

Quoting can be such a headache for the novice, in shell programming,
and especially in awk.

Art Povelones posted a long tutorial on shell quoting on 1999/09/30
which is probably too much detail to repeat with the FAQ; if you
could use it, search via <http://groups.google.com/>.

Tim Maher offered his <http://www.consultix-inc.com/quoting.txt>.

This approach is probably the best, and easiest to understand and
maintain, for most purposes:  (the '@@' is quoted to ensure the
shell will copy verbatim, not interpreting environment variable
substitutions etc.)

    cat <<'@@' > /tmp/never$$.awk
    { print "Never say can't." }
    @@
    awk -f /tmp/never$$.awk; rm /tmp/never$$.awk

If you enjoy testing your shell's quoting behavior frequently, you
could try these:

    (see below for a verbose explanation of the first one, with 7 quotes)

    awk 'BEGIN { q="'"'"'";print "Never say can"q"t."; exit }'
    nawk -v q="'" 'BEGIN { print "Never say can"q"t."; exit }'
    awk 'BEGIN { q=sprintf("%c",39); print "Never say can"q"t."; exit }'
    awk 'BEGIN { q=sprintf("%c",39); print "Never say \"can"q"t.\""; exit }'

However, you would also have to know why you could not use this:

    awk 'BEGIN { q="\'"; print "Never say \"can"q"t.\""; exit }'

explanation of the 7-quote example:

note that it is quoted three different ways:

    awk 'BEGIN { q="'
                     "'"
                        '";print "Never say can"q"t."; exit }'

and that argument comes out as the single string (with embedded spaces)

    BEGIN { q="'";print "Never say can"q"t."; exit }

which is the same as

    BEGIN { q="'"; print "Never say can" q "t."; exit }
                          ^^^^^^^^^^^^^  ^  ^^
                          |           |  |  ||
                          |           |  |  ||
                          vvvvvvvvvvvvv  |  ||
                          Never say can  v  ||
                                         '  vv
                                            t.

which, quite possibly with too much effort to be worth it, gets you

                          Never say can't.


14.3 ENVIRON[] and "env"|getline

   Modern versions of new awk (gawk, mawk, Bell Labs awk, any POSIX
   awk) all provide an array named ENVIRON.  The array is indexed by
   environment variable name; the value is that variable's value.
   For instance, ENVIRON["HOME"] might be "/home/chris".  To print
   out all the names and values, use a simple loop:

        for (i in ENVIRON)
                printf("ENVIRON['%s'] = '%s'\n", i, ENVIRON)

   What if my awk doesn't have ENVIRON[]?

   Short answer, get a better awk.  There are many freely available
   versions.

   Longer answer, on Unix you can use a pipe from the `env' or
   `printenv' commands, but this is less pretty, and may be a
   problem if the values contain newlines:

        # test this on your system before you depend on it!
        while ( ("env" | getline line) >0 )
        {
                varname=line
                varvalue=line
                sub(/=.*$/,"",varname)
                sub(/^[^=]*=/,"",varvalue)
                print "var [" varname "]='" varvalue "'"
        }

14.4 exporting environment variables back to the parent process

   How can I put values into the environment of the program that
   called my awk program?

   Short answer, you can't.  Unix ain't Plan 9, and you can't tweak
   the parent's address space.

   (DOS isn't even Unix, so it lets any program overwrite any memory
   location, including the parent's environment space.  But the
   details are [obviously] going to be fairly icky.  Avoid.)

   Longer answer, write the results in a form the shell can parse
   to a temporary file, and have the shell "source" the file after
   running the awk program:

        awk 'BEGIN { printf("NEWVAR='%s'\n", somevalue) }' > /tmp/awk.$$
        . /tmp/awk.$$        # sh/ksh/bash/pdksh/zsh etc
        rm /tmp/awk.$$

   With many shells, you can use `eval', but this is also cumbersome:

        eval `awk 'BEGIN { print "NEWVAR=" somevalue }'`

   Csh syntax and more robust use of quotation marks are left as
   exercises for the reader.