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SHMCAT(1)              DragonFly General Commands Manual             SHMCAT(1)


NAME

       shmcat - dump shared memory segments, files, standard input and/or text


SYNOPSIS

       shmcat [ OPTION ]... [ OPERAND ]...


DESCRIPTION

       Dump shared memory segments, files, standard input and/or text to
       standard output. If no OPERAND is given, read standard input only. If
       more than one OPERAND is given, dump them in order. If some of the
       OPERANDs cannot be read, shmcat prints an error message to standard
       error and tries to continue with the other OPERANDs.

       Most modern systems support two APIs for shared memory:

       The older one is commonly known as the System V API. It uses numeric
       keys and IDs as identifiers and consists of system calls like
       shmget(2), shmat(2) and shmdt(2).

       The newer API is called the POSIX shared memory API. It uses names in
       string form as identifiers. It treats shared memory similar to files,
       which are opened with shm_open(3) and then mapped into the program
       address space via mmap(2). Please note that POSIX shared memory is not
       supported by all versions of shmcat.

       If shmcat has been compiled without getopt_long(3) support, only the
       short, one character OPTIONs and OPERANDs can be used. Otherwise the
       long ones are also available. When a long OPTION or OPERAND needs an
       argument, the short versions do so, as well.


OPTIONS

       -h, -?, --help
              Display usage information and quit without dumping anything.

       -V, --version
              Show version information and quit without further action.


OPERANDS

       -f, --file=FILENAME
              Dump the contents of the given file.

       -i, --stdin
              Dump standard input.

       -M, --shmkey=KEY
              Dump the System V shared memory segment with the given key. The
              key can be given as a decimal (no prefix), octal (prefix 0), or
              hexadecimal (prefix 0x) number. It can, for example, be obtained
              using the ipcs(1) or the ftok(1) tool.

       -m, --shmid=ID
              Dump the System V shared memory segment with the given id. The
              id can be given as a decimal (no prefix), octal (prefix 0), or
              hexadecimal (prefix 0x) number. It can, for example, be obtained
              using the ipcs(1) tool.

       -n, --newline
              Add a line feed.

       -p, --posix-shm=NAME
              Dump the POSIX shared memory segment with the given name (not
              supported in all installations).

       -t, --text=TEXT
              Print the given text.


EXIT CODES

       0      No errors, every OPERAND requested was dumped

       1      There was an error while dumping at least one OPERAND, but the
              program continued with the other OPERANDs (if given)

       2      There was a fatal error, usually this means that shmcat could
              not write to standard output

       10     Wrong usage of the program


NOTES

       Usually, when you dump shared memory segments, you should redirect the
       output of shmcat to a file or a program like od(1), because shared
       memory data usually has a binary form and thus it may contain non-
       printable characters. You also probably want to suspend the processes
       writing to the shared memory object in order to get a consistent dump.


AUTHOR

       Stefan Gast


SEE ALSO

       ftok(1), ipcs(1), shmat(2), shmget(2), shm_open(3)

shmcat(1)                        November 2012                       SHMCAT(1)

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