Skunkware 5/Skunkware 5.iso/man/cat.1/perlvar.1

Text File | 1995-07-25 | 31KB | 793 lines

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     NNNNAAAAMMMMEEEE
          perlvar - Perl predefined variables

     DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
          PPPPrrrreeeeddddeeeeffffiiiinnnneeeedddd NNNNaaaammmmeeeessss

          The following names have special meaning to Perl.  Most of
          the punctuational names have reasonable mnemonics, or
          analogues in one of the shells.  Nevertheless, if you wish
          to use the long variable names, you just need to say

              use English;

          at the top of your program.  This will alias all the short
          names to the long names in the current package.  Some of
          them even have medium names, generally borrowed from aaaawwwwkkkk.

          To go a step further, those variables that depend on the
          currently selected filehandle may instead be set by calling
          an object method on the FileHandle object.  (Summary lines
          below for this contain the word HANDLE.)  First you must say

              use FileHandle;

          after which you may use either

              method HANDLE EXPR

          or

              HANDLE->method(EXPR)

          Each of the methods returns the old value of the FileHandle
          attribute.  The methods each take an optional EXPR, which if
          supplied specifies the new value for the FileHandle
          attribute in question.  If not supplied, most of the methods
          do nothing to the current value, except for _a_u_t_o_f_l_u_s_h(),
          which will assume a 1 for you, just to be different.

          A few of these variables are considered "read-only".  This
          means that if you try to assign to this variable, either
          directly or indirectly through a reference.  If you attempt
          to do so, you'll raise a run-time exception.

          $ARG

          $_      The default input and pattern-searching space.  The
                  following pairs are equivalent:

                      while (<>) {...}    # only equivalent in while!
                      while ($_ = <>) {...}




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                      /^Subject:/
                      $_ =~ /^Subject:/

                      tr/a-z/A-Z/
                      $_ =~ tr/a-z/A-Z/

                      chop
                      chop($_)

                  (Mnemonic: underline is understood in certain
                  operations.)

          $<_d_i_g_i_t>
                  Contains the subpattern from the corresponding set
                  of parentheses in the last pattern matched, not
                  counting patterns matched in nested blocks that have
                  been exited already.  (Mnemonic: like \digit.) These
                  variables are all read-only.

          $MATCH

          $&      The string matched by the last successful pattern
                  match (not counting any matches hidden within a
                  BLOCK or _e_v_a_l() enclosed by the current BLOCK).
                  (Mnemonic: like & in some editors.)  This variable
                  is read-only.

          $PREMATCH

          $`      The string preceding whatever was matched by the
                  last successful pattern match (not counting any
                  matches hidden within a BLOCK or eval enclosed by
                  the current BLOCK).  (Mnemonic: ` often precedes a
                  quoted string.)  This variable is read-only.

          $POSTMATCH

          $'      The string following whatever was matched by the
                  last successful pattern match (not counting any
                  matches hidden within a BLOCK or _e_v_a_l() enclosed by
                  the current BLOCK).  (Mnemonic: ' often follows a
                  quoted string.)  Example:

                      $_ = 'abcdefghi';
                      /def/;
                      print "$`:$&:$'\n";         # prints abc:def:ghi

                  This variable is read-only.

          $LAST_PAREN_MATCH





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          $+      The last bracket matched by the last search pattern.
                  This is useful if you don't know which of a set of
                  alternative patterns matched.  For example:

                      /Version: (.*)|Revision: (.*)/ && ($rev = $+);

                  (Mnemonic: be positive and forward looking.) This
                  variable is read-only.

          $MULTILINE_MATCHING

          $*      Set to 1 to do multiline matching within a string, 0
                  to tell Perl that it can assume that strings contain
                  a single line, for the purpose of optimizing pattern
                  matches.  Pattern matches on strings containing
                  multiple newlines can produce confusing results when
                  "$*" is 0.  Default is 0.  (Mnemonic: * matches
                  multiple things.)  Note that this variable only
                  influences the interpretation of "^" and "$".  A
                  literal newline can be searched for even when $* ==
                  0.

                  Use of "$*" is deprecated in Perl 5.

          input_line_number HANDLE EXPR

          $INPUT_LINE_NUMBER

          $NR

          $.      The current input line number of the last filehandle
                  that was read.  This variable should be considered
                  read-only. Remember that only an explicit close on
                  the filehandle resets the line number.  Since "<>"
                  never does an explicit close, line numbers increase
                  across ARGV files (but see examples under _e_o_f()).
                  (Mnemonic: many programs use "." to mean the current
                  line number.)

          input_record_separator HANDLE EXPR

          $INPUT_RECORD_SEPARATOR

          $RS

          $/      The input record separator, newline by default.
                  Works like aaaawwwwkkkk's RS variable, including treating
                  blank lines as delimiters if set to the null string.
                  You may set it to a multicharacter string to match a
                  multi-character delimiter.  Note that setting it to
                  "\n\n" means something slightly different than
                  setting it to "", if the file contains consecutive



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                  blank lines.  Setting it to "" will treat two or
                  more consecutive blank lines as a single blank line.
                  Setting it to "\n\n" will blindly assume that the
                  next input character belongs to the next paragraph,
                  even if it's a newline.  (Mnemonic: / is used to
                  delimit line boundaries when quoting poetry.)

                      undef $/;
                      $_ = <FH>;          # whole file now here
                      s/\n[ \t]+/ /g;


          autoflush HANDLE EXPR

          $OUTPUT_AUTOFLUSH

          $|      If set to nonzero, forces a flush after every write
                  or print on the currently selected output channel.
                  Default is 0.  Note that STDOUT will typically be
                  line buffered if output is to the terminal and block
                  buffered otherwise.  Setting this variable is useful
                  primarily when you are outputting to a pipe, such as
                  when you are running a Perl script under rsh and
                  want to see the output as it's happening.
                  (Mnemonic: when you want your pipes to be piping
                  hot.)

          output_field_separator HANDLE EXPR

          $OUTPUT_FIELD_SEPARATOR

          $OFS

          $,      The output field separator for the print operator.
                  Ordinarily the print operator simply prints out the
                  comma separated fields you specify.  In order to get
                  behavior more like aaaawwwwkkkk, set this variable as you
                  would set aaaawwwwkkkk's OFS variable to specify what is
                  printed between fields.  (Mnemonic: what is printed
                  when there is a , in your print statement.)

          output_record_separator HANDLE EXPR

          $OUTPUT_RECORD_SEPARATOR

          $ORS

          $\      The output record separator for the print operator.
                  Ordinarily the print operator simply prints out the
                  comma separated fields you specify, with no trailing
                  newline or record separator assumed.  In order to
                  get behavior more like aaaawwwwkkkk, set this variable as you



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                  would set aaaawwwwkkkk's ORS variable to specify what is
                  printed at the end of the print.  (Mnemonic: you set
                  "$\" instead of adding \n at the end of the print.
                  Also, it's just like /, but it's what you get "back"
                  from Perl.)

          $LIST_SEPARATOR

          $
          This is like "$," except that it applies to array values
          interpolated into a double-quoted string (or similar
          interpreted string).  Default is a space.  (Mnemonic:
          obvious, I think.)

          $SUBSCRIPT_SEPARATOR

          $SUBSEP

          $;      The subscript separator for multi-dimensional array
                  emulation.  If you refer to a hash element as

                      $foo{$a,$b,$c}

                  it really means

                      $foo{join($;, $a, $b, $c)}

                  But don't put

                      @foo{$a,$b,$c}      # a slice--note the @

                  which means

                      ($foo{$a},$foo{$b},$foo{$c})

                  Default is "\034", the same as SUBSEP in aaaawwwwkkkk.  Note
                  that if your keys contain binary data there might
                  not be any safe value for "$;".  (Mnemonic: comma
                  (the syntactic subscript separator) is a semi-
                  semicolon.  Yeah, I know, it's pretty lame, but "$,"
                  is already taken for something more important.)

                  Consider using "real" multi-dimensional arrays in
                  Perl 5.

          $OFMT

          $#      The output format for printed numbers.  This
                  variable is a half-hearted attempt to emulate aaaawwwwkkkk's
                  OFMT variable.  There are times, however, when aaaawwwwkkkk
                  and Perl have differing notions of what is in fact
                  numeric.  Also, the initial value is %.20g rather



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                  than %.6g, so you need to set "$#" explicitly to get
                  aaaawwwwkkkk's value.  (Mnemonic: # is the number sign.)

                  Use of "$#" is deprecated in Perl 5.

          format_page_number HANDLE EXPR

          $FORMAT_PAGE_NUMBER

          $%      The current page number of the currently selected
                  output channel.  (Mnemonic: % is page number in
                  nnnnrrrrooooffffffff.)

          format_lines_per_page HANDLE EXPR

          $FORMAT_LINES_PER_PAGE

          $=      The current page length (printable lines) of the
                  currently selected output channel.  Default is 60.
                  (Mnemonic: = has horizontal lines.)

          format_lines_left HANDLE EXPR

          $FORMAT_LINES_LEFT

          $-      The number of lines left on the page of the
                  currently selected output channel.  (Mnemonic:
                  lines_on_page - lines_printed.)

          format_name HANDLE EXPR

          $FORMAT_NAME

          $~      The name of the current report format for the
                  currently selected output channel.  Default is name
                  of the filehandle.  (Mnemonic: brother to "$^".)

          format_top_name HANDLE EXPR

          $FORMAT_TOP_NAME

          $^      The name of the current top-of-page format for the
                  currently selected output channel.  Default is name
                  of the filehandle with _TOP appended.  (Mnemonic:
                  points to top of page.)

          format_line_break_characters HANDLE EXPR

          $FORMAT_LINE_BREAK_CHARACTERS

          $:      The current set of characters after which a string
                  may be broken to fill continuation fields (starting



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                  with ^) in a format.  Default is " \n-", to break on
                  whitespace or hyphens.  (Mnemonic: a "colon" in
                  poetry is a part of a line.)

          format_formfeed HANDLE EXPR

          $FORMAT_FORMFEED

          $^L     What formats output to perform a formfeed.  Default
                  is \f.

          $ACCUMULATOR

          $^A     The current value of the _w_r_i_t_e() accumulator for
                  _f_o_r_m_a_t() lines.  A format contains _f_o_r_m_l_i_n_e()
                  commands that put their result into $^A.  After
                  calling its format, _w_r_i_t_e() prints out the contents
                  of $^A and empties.  So you never actually see the
                  contents of $^A unless you call _f_o_r_m_l_i_n_e() yourself
                  and then look at it.  See the _p_e_r_l_f_o_r_m manpage and
                  the formline() entry in the _p_e_r_l_f_u_n_c manpage.

          $CHILD_ERROR

          $?      The status returned by the last pipe close, backtick
                  (``) command, or _s_y_s_t_e_m() operator.  Note that this
                  is the status word returned by the _w_a_i_t() system
                  call, so the exit value of the subprocess is
                  actually ($? >> 8).  Thus on many systems, $? & 255
                  gives which signal, if any, the process died from,
                  and whether there was a core dump.  (Mnemonic:
                  similar to sssshhhh and kkkksssshhhh.)

          $OS_ERROR

          $ERRNO

          $!      If used in a numeric context, yields the current
                  value of errno, with all the usual caveats.  (This
                  means that you shouldn't depend on the value of "$!"
                  to be anything in particular unless you've gotten a
                  specific error return indicating a system error.)
                  If used in a string context, yields the
                  corresponding system error string.  You can assign
                  to "$!" in order to set _e_r_r_n_o if, for instance, you
                  want "$!" to return the string for error _n, or you
                  want to set the exit value for the _d_i_e() operator.
                  (Mnemonic: What just went bang?)

          $EVAL_ERROR





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          $@      The Perl syntax error message from the last _e_v_a_l()
                  command.  If null, the last _e_v_a_l() parsed and
                  executed correctly (although the operations you
                  invoked may have failed in the normal fashion).
                  (Mnemonic: Where was the syntax error "at"?)

          $PROCESS_ID

          $PID

          $$      The process number of the Perl running this script.
                  (Mnemonic: same as shells.)

          $REAL_USER_ID

          $UID

          $<      The real uid of this process.  (Mnemonic: it's the
                  uid you came _F_R_O_M, if you're running setuid.)

          $EFFECTIVE_USER_ID

          $EUID

          $>      The effective uid of this process.  Example:

                      $< = $>;            # set real to effective uid
                      ($<,$>) = ($>,$<);  # swap real and effective uid

                  (Mnemonic: it's the uid you went _T_O, if you're
                  running setuid.)  Note: "$<" and "$>" can only be
                  swapped on machines supporting _s_e_t_r_e_u_i_d().

          $REAL_GROUP_ID

          $GID

          $(      The real gid of this process.  If you are on a
                  machine that supports membership in multiple groups
                  simultaneously, gives a space separated list of
                  groups you are in.  The first number is the one
                  returned by _g_e_t_g_i_d(), and the subsequent ones by
                  _g_e_t_g_r_o_u_p_s(), one of which may be the same as the
                  first number.  (Mnemonic: parentheses are used to
                  _G_R_O_U_P things.  The real gid is the group you _L_E_F_T,
                  if you're running setgid.)

          $EFFECTIVE_GROUP_ID

          $EGID





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          $)      The effective gid of this process.  If you are on a
                  machine that supports membership in multiple groups
                  simultaneously, gives a space separated list of
                  groups you are in.  The first number is the one
                  returned by _g_e_t_e_g_i_d(), and the subsequent ones by
                  _g_e_t_g_r_o_u_p_s(), one of which may be the same as the
                  first number.  (Mnemonic: parentheses are used to
                  _G_R_O_U_P things.  The effective gid is the group that's
                  _R_I_G_H_T for you, if you're running setgid.)

                  Note: "$<", "$>", "$(" and "$)" can only be set on
                  machines that support the corresponding
                  _s_e_t[_r_e][_u_g]_i_d() routine.  "$(" and "$)" can only be
                  swapped on machines supporting _s_e_t_r_e_g_i_d().

          $PROGRAM_NAME

          $0      Contains the name of the file containing the Perl
                  script being executed.  Assigning to "$0" modifies
                  the argument area that the _p_s(1) program sees.  This
                  is more useful as a way of indicating the current
                  program state than it is for hiding the program
                  you're running.  (Mnemonic: same as sssshhhh and kkkksssshhhh.)

          $[      The index of the first element in an array, and of
                  the first character in a substring.  Default is 0,
                  but you could set it to 1 to make Perl behave more
                  like aaaawwwwkkkk (or Fortran) when subscripting and when
                  evaluating the _i_n_d_e_x() and _s_u_b_s_t_r() functions.
                  (Mnemonic: [ begins subscripts.)

                  As of Perl 5, assignment to "$[" is treated as a
                  compiler directive, and cannot influence the
                  behavior of any other file.  Its use is discouraged.

          $PERL_VERSION

          $]      The string printed out when you say perl -v.  It can
                  be used to determine at the beginning of a script
                  whether the perl interpreter executing the script is
                  in the right range of versions.  If used in a
                  numeric context, returns the version + patchlevel /
                  1000.  Example:

                      # see if getc is available
                      ($version,$patchlevel) =
                               $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
                      print STDERR "(No filename completion available.)\n"
                               if $version * 1000 + $patchlevel < 2016;

                  or, used numerically,




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                      warn "No checksumming!\n" if $] < 3.019;

                  (Mnemonic: Is this version of perl in the right
                  bracket?)

          $DEBUGGING

          $^D     The current value of the debugging flags.
                  (Mnemonic: value of ----DDDD switch.)

          $SYSTEM_FD_MAX

          $^F     The maximum system file descriptor, ordinarily 2.
                  System file descriptors are passed to _e_x_e_c()ed
                  processes, while higher file descriptors are not.
                  Also, during an _o_p_e_n(), system file descriptors are
                  preserved even if the _o_p_e_n() fails.  (Ordinary file
                  descriptors are closed before the _o_p_e_n() is
                  attempted.)  Note that the close-on-exec status of a
                  file descriptor will be decided according to the
                  value of $^F at the time of the open, not the time
                  of the exec.

          $INPLACE_EDIT

          $^I     The current value of the inplace-edit extension.
                  Use undef to disable inplace editing.  (Mnemonic:
                  value of ----iiii switch.)

          $PERLDB

          $^P     The internal flag that the debugger clears so that
                  it doesn't debug itself.  You could conceivable
                  disable debugging yourself by clearing it.

          $BASETIME

          $^T     The time at which the script began running, in
                  seconds since the epoch (beginning of 1970).  The
                  values returned by the ----MMMM, ----AAAA and ----CCCC filetests are
                  based on this value.

          $WARNING

          $^W     The current value of the warning switch, either TRUE
                  or FALSE.  (Mnemonic: related to the ----wwww switch.)

          $EXECUTABLE_NAME

          $^X     The name that the Perl binary itself was executed
                  as, from C's argv[0].




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          $ARGV   contains the name of the current file when reading
                  from <>.

          @ARGV   The array @ARGV contains the command line arguments
                  intended for the script.  Note that $#ARGV is the
                  generally number of arguments minus one, since
                  $ARGV[0] is the first argument, _N_O_T the command
                  name.  See "$0" for the command name.

          @INC    The array @INC contains the list of places to look
                  for Perl scripts to be evaluated by the do EXPR,
                  require, or use constructs.  It initially consists
                  of the arguments to any ----IIII command line switches,
                  followed by the default Perl library, probably
                  "/usr/local/lib/perl", followed by ".", to represent
                  the current directory.

          %INC    The hash %INC contains entries for each filename
                  that has been included via do or require.  The key
                  is the filename you specified, and the value is the
                  location of the file actually found.  The require
                  command uses this array to determine whether a given
                  file has already been included.

          $ENV{expr}
                  The hash %ENV contains your current environment.
                  Setting a value in ENV changes the environment for
                  child processes.

          $SIG{expr}
                  The hash %SIG is used to set signal handlers for
                  various signals.  Example:

                      sub handler {       # 1st argument is signal name
                          local($sig) = @_;
                          print "Caught a SIG$sig--shutting down\n";
                          close(LOG);
                          exit(0);
                      }

                      $SIG{'INT'} = 'handler';
                      $SIG{'QUIT'} = 'handler';
                      ...
                      $SIG{'INT'} = 'DEFAULT';    # restore default action
                      $SIG{'QUIT'} = 'IGNORE';    # ignore SIGQUIT

                  The %SIG array only contains values for the signals
                  actually set within the Perl script.  Here are some
                  other examples:






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                      $SIG{PIPE} = Plumber;       # SCARY!!
                      $SIG{"PIPE"} = "Plumber";   # just fine, assumes main::Plumber
                      $SIG{"PIPE"} = \&Plumber;   # just fine; assume current Plumber
                      $SIG{"PIPE"} = Plumber();   # oops, what did Plumber() return??

                  The one marked scary is problematic because it's a
                  bareword, which means sometimes it's a string
                  representing the function, and sometimes it's going
                  to call the subroutine call right then and there!
                  Best to be sure and quote it or take a reference to
                  it.  *Plumber works too.  See <perlsubs>.












































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