a

ksh 实现的基于hpux下的性能数据以及故障的采集程序。可以作为新手练手使用

      can be started.

      If a command is followed by & and job control is inactive, the default
      standard input for the command is the empty file /dev/null.
      Otherwise, the environment for the execution of a command contains the
      file descriptors of the invoking shell as modified by input/output
      specifications.

    Environment
      The environment (see environ(5)) is a list of name-value pairs passed
      to an executed program much like a normal argument list.	The names
      must be identifiers and the values are character strings.	 The shell
      interacts with the environment in several ways.  When invoked, the
      shell scans the environment and creates a parameter for each name
      found, gives it the corresponding value, and marks it export.
      Executed commands inherit the environment.  If the user modifies the
      values of these parameters or creates new ones by using the export or
      typeset -x commands, the values become part of the environment.  The
      environment seen by any executed command is thus composed of any
      name-value pairs originally inherited by the shell whose values can be
      modified by the current shell, plus any additions which must be noted
      in export or typeset -x commands.

      The environment for any simple-command or function can be augmented by
      prefixing it with one or more parameter assignments.  A parameter
      assignment argument takes the form identifier=value.  For example,

	   TERM=450 cmd args

      and

	   (export TERM; TERM=450; cmd args)

      are equivalent (as far as the above execution of cmd is concerned
      except for special commands listed below that are preceded by a
      percent sign).

      If the -k option is set, all parameter assignment arguments are placed
      in the environment, even if they occur after the command name.  The
      following echo statement prints a=b c.  After the -k option is set,
      the second echo statement prints only c:

	   echo a=b c
	   set -k
	   echo a=b c





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      This feature is intended for use with scripts written for early
      versions of the shell, and its use in new scripts is strongly
      discouraged.  It is likely to disappear someday.

    Functions
      The function keyword (described in the Commands section above) is used
      to define shell functions.  Shell functions are read and stored
      internally.  Alias names are resolved when the function is read.
      Functions are executed like commands, with the arguments passed as
      positional parameters (see Execution below).

      Functions execute in the same process as the caller except that
      command substitution of a function creates a new process.	 Functions
      share all files and present working directory with the caller.  Traps
      caught by the caller are reset to their default action inside the
      function.	 If a function does not catch or specifically ignore a trap
      condition, the function terminates and the condition is passed on to
      the caller.  A trap on EXIT set inside a function is executed after
      the function completes in the environment of the caller.	Ordinarily,
      variables are shared between the calling program and the function.
      However, the typeset special command used within a function defines
      local variables whose scope includes the current function and all
      functions it calls.

      The special command return is used to return from function calls.
      Errors within functions return control to the caller.

      Function identifiers can be listed with the +f option of the typeset
      special command.	Function identifiers and the associated text of the
      functions can be listed with the -f option.  Functions can be
      undefined with the -f option of the unset special command.

      Ordinarily, functions are unset when the shell executes a shell
      script.  The -xf option of the typeset command allows a function to be
      exported to scripts that are executed without reinvoking the shell.
      Functions that must be defined across separate invocations of the
      shell should be placed in the ENV file.

    Jobs
      If the monitor option of the set command is turned on, an interactive
      shell associates a job with each pipeline.  It keeps a table of
      current jobs, printed by the jobs command, and assigns them small
      integer numbers.	When a job is started asynchronously with &, the
      shell prints a line resembling:

	   [1] 1234

      indicating that job number 1 was started asynchronously and had one
      (top-level) process whose process ID was 1234.





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      If you are running a job and want to do something else, type the
      suspend character (usually ^Z (Ctrl-Z)) to send a STOP signal to the
      current job.  The shell then indicates that the job has been
      `Stopped', and prints another prompt.  The state of this job can be
      manipulated by using the bg command to put it in the background,
      running other commands (while it is stopped or running in the
      background), and eventually restarting or returning the job to the
      foreground by using the fg command.  A ^Z takes effect immediately and
      resembles an interrupt, since pending output and unread input are
      discarded when ^Z is typed.

      A job run in the background stops if it tries to read from the
      terminal.	 Background jobs normally are allowed to produce output, but
      can be disabled by giving the stty tostop command.  If the user sets
      this tty option, background jobs stop when trying to produce output.

      There are several ways to refer to jobs in the shell.  A job can be
      referred to by the process ID of any process in the job or by one of
      the following:

	   %number	       The job with the given number.
	   %string	       Any job whose command line begins with
			       string.
	   %?string	       Any job whose command line contains string.
	   %%		       Current job.
	   %+		       Equivalent to %%.
	   %-		       Previous job.

      The shell learns immediately when a process changes state.  It informs
      the user when a job is blocked and prevented from further progress,
      but only just before it prints a prompt.

      When the monitor mode is on, each background job that completes
      triggers any trap set for CHLD.

      Attempting to leave the shell while jobs are running or stopped
      produces the warning, You have stopped (running) jobs.  Use the jobs
      command to identify them.	 An immediate attempt to exit again
      terminates the stopped jobs; the shell does not produce a warning the
      second time.

    Signals
      The INT and QUIT signals for an invoked command are ignored if the
      command is followed by & and the monitor option is off.  Otherwise,
      signals have the values inherited by the shell from its parent, with
      the exception of signal 11 (but see also the trap command below).

    Execution
      Substitutions are made each time a command is executed.  If the
      command name matches one of the Special Commands listed below, it is
      executed within the current shell process.  Next, ksh checks the



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      command name to determine whether it matches one of the user-defined
      functions.  If it does, ksh saves the positional parameters and then
      sets them to the arguments of the function call.	The positional
      parameter 0 is set to the function name.	When the function completes
      or issues a return, ksh restores the positional parameter list and
      executes any trap set on EXIT within the function.  The value of a
      function is the value of the last command executed.  A function is
      executed in the current shell process.  If a command name is not a
      special command or a user-defined function, ksh creates a process and
      attempts to execute the command using exec (see exec(2)).

      The shell parameter PATH defines the search path for the directory
      containing the command.  Alternative directory names are separated by
      a colon (:).  The default path is /usr/bin: (specifying /usr/bin and
      the current directory in that order).  Note that the current directory
      is specified by a null path name which can appear immediately after
      the equals sign, between colon delimiters, or at the end of the path
      list.  The search path is not used if the command name contains a /.
      Otherwise, each directory in the path is searched for an executable
      file.  If the file has execute permissions but is not a directory or
      an executable object code file, it is assumed to be a script file,
      which is a file of data for an interpreter.  If the first two
      characters of the script file are #!, exec (see exec(2)) expects an
      interpreter path name to follow.	exec then attempts to execute the
      specified interpreter as a separate process to read the entire script
      file.  If a call to exec fails, /usr/bin/ksh is spawned to interpret
      the script file.	All non-exported aliases, functions, and named
      parameters are removed in this case.  If the shell command file does
      not have read permission, or if the setuid and/or setgid bits are set
      on the file, the shell executes an agent to set up the permissions and
      execute the shell with the shell command file passed down as an open
      file.  A parenthesized command is also executed in a sub-shell without
      removing non-exported quantities.

    Command Re-entry
      The text of the last HISTSIZE (default 128) commands entered from a
      terminal device is saved in a history file.  The file
      $HOME/.sh_history is used if the HISTFILE variable is not set or
      writable.	 A shell can access the commands of all interactive shells
      that use the same named HISTFILE.	 The special command fc is used to
      list or edit a portion of this file.  The portion of the file to be
      edited or listed can be selected by number or by giving the first
      character or characters of the command.  A single command or range of
      commands can be specified.  If no editor program is specified as an
      argument to fc, the value of the FCEDIT parameter is used.  If FCEDIT
      is not defined, /usr/bin/ed is used.  The edited command is printed
      and re-executed upon leaving the editor.	The editor name - is used to
      skip the editing phase and to re-execute the command.  In this case a
      substitution parameter of the form old=new can be used to modify the
      command before execution.	 For example, if r is aliased to fc -e -,
      typing r bad=good c re-executes the most recent command that starts



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      with the letter c and replaces the first occurrence of the string bad
      with the string good.

      The history file will be trimmed when all of the following conditions
      occurs:

	   Its size is greater than four kilobytes.

	   The number of commands in it is more than HISTSIZE.

	   The file has not been modified in the last ten minutes.

	   The user has write permission for the directory in which the
	   history file resides.

      If any one of the above conditions does not occur, the history file
      will not be trimmed. When the history file is trimmed, the latest
      HISTSIZE commands will be available in the history file.

    Special Commands
      The following simple-commands are executed in the shell process.	They
      permit input/output redirection.	Unless otherwise indicated, file
      descriptor 1 is the default output location and the exit status, when
      there are no syntax errors, is zero.  Commands that are preceded by %
      or %% are treated specially in the following ways:

	   1.  Variable assignment lists preceding the command remain in
	       effect when the command completes.
	   2.  I/O redirections are processed after variable assignments.
	   3.  Certain errors cause a script that contains them to abort.
	   4.  Words following a command preceded by %% that are in the
	       format of a variable assignment are expanded with the same
	       rules as a variable assignment.	This means that tilde
	       substitution is performed after the = sign and word splitting
	       and file name generation are not performed.

      % : [arg ...]  The command only expands parameters.  A zero exit code
		     is returned.

      % . file [arg ...]
		     Read and execute commands from file and return.  The
		     commands are executed in the current shell environment.
		     The search path specified by PATH is used to find the
		     directory containing file.	 If any arguments arg are
		     given, they become the positional parameters.
		     Otherwise the positional parameters are unchanged.	 The
		     exit status is the exit status of the last command
		     executed.	It is not necessary that the execute
		     permission bit be set for file.





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 ksh(1)								      ksh(1)




      %% alias [-tx] [name[=value] ...]
		     alias with no arguments prints the list of aliases in
		     the form name=value on standard output.  An alias is
		     defined for each name whose value is given.  A trailing
		     space in value causes the next word to be checked for
		     alias substitution.  The -t option is used to set and
		     list tracked aliases.  The value of a tracked alias is
		     the full path name corresponding to the given name.