=item 2.
Contained in the file specified by the first filename on the command line.
-(Note that systems supporting the #! notation invoke interpreters this way.)
+(Note that systems supporting the #! notation invoke interpreters this
+way. See L<Location of Perl>.)
=item 3.
execute standard input instead of your script. And a partial B<-I> switch
could also cause odd results.
+Some switches do care if they are processed twice, for instance combinations
+of B<-l> and B<-0>. Either put all the switches after the 32 character
+boundary (if applicable), or replace the use of B<-0>I<digits> by
+C<BEGIN{ $/ = "\0digits"; }>.
+
Parsing of the #! switches starts wherever "perl" is mentioned in the line.
The sequences "-*" and "- " are specifically ignored so that you could,
if you were so inclined, say
#!/bin/sh -- # -*- perl -*- -p
- eval 'exec /usr/bin/perl $0 -S ${1+"$@"}'
+ eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
to let Perl see the B<-p> switch.
The Win95/NT installation, when using the Activeware port of Perl,
will modify the Registry to associate the .pl extension with the perl
interpreter. If you install another port of Perl, including the one
-in the win32 directory of the Perl distribution, then you'll have to
+in the Win32 directory of the Perl distribution, then you'll have to
modify the Registry yourself.
=item Macintosh
-Macintosh perl scripts will have the the appropriate Creator and
+Macintosh perl scripts will have the appropriate Creator and
Type, so that double-clicking them will invoke the perl application.
=back
There is no general solution to all of this. It's just a mess.
+=head2 Location of Perl
+
+It may seem obvious to say, but Perl is useful only when users can
+easily find it. When possible, it's good for both B</usr/bin/perl> and
+B</usr/local/bin/perl> to be symlinks to the actual binary. If that
+can't be done, system administrators are strongly encouraged to put
+(symlinks to) perl and its accompanying utilities, such as perldoc, into
+a directory typically found along a user's PATH, or in another obvious
+and convenient place.
+
+In this documentation, C<#!/usr/bin/perl> on the first line of the script
+will stand in for whatever method works on your system.
+
=head2 Switches
A single-character switch may be combined with the following switch, if
installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
Devel::DProf profiler. See L<perldebug>.
-=item B<-D>I<number>
+=item B<-D>I<letters>
-=item B<-D>I<list>
+=item B<-D>I<number>
sets debugging flags. To watch how it executes your script, use
-B<-D14>. (This works only if debugging is compiled into your
-Perl.) Another nice value is B<-D1024>, which lists your compiled
-syntax tree. And B<-D512> displays compiled regular expressions. As an
-alternative specify a list of letters instead of numbers (e.g., B<-D14> is
+B<-Dtls>. (This works only if debugging is compiled into your
+Perl.) Another nice value is B<-Dx>, which lists your compiled
+syntax tree. And B<-Dr> displays compiled regular expressions. As an
+alternative, specify a number instead of list of letters (e.g., B<-D14> is
equivalent to B<-Dtls>):
- 1 p Tokenizing and Parsing
- 2 s Stack Snapshots
- 4 l Label Stack Processing
- 8 t Trace Execution
- 16 o Operator Node Construction
- 32 c String/Numeric Conversions
- 64 P Print Preprocessor Command for -P
- 128 m Memory Allocation
- 256 f Format Processing
- 512 r Regular Expression Parsing
- 1024 x Syntax Tree Dump
- 2048 u Tainting Checks
- 4096 L Memory Leaks (not supported anymore)
- 8192 H Hash Dump -- usurps values()
- 16384 X Scratchpad Allocation
- 32768 D Cleaning Up
+ 1 p Tokenizing and parsing
+ 2 s Stack snapshots
+ 4 l Context (loop) stack processing
+ 8 t Trace execution
+ 16 o Method and overloading resolution
+ 32 c String/numeric conversions
+ 64 P Print preprocessor command for -P
+ 128 m Memory allocation
+ 256 f Format processing
+ 512 r Regular expression parsing and execution
+ 1024 x Syntax tree dump
+ 2048 u Tainting checks
+ 4096 L Memory leaks (needs C<-DLEAKTEST> when compiling Perl)
+ 8192 H Hash dump -- usurps values()
+ 16384 X Scratchpad allocation
+ 32768 D Cleaning up
+
+All these flags require C<-DDEBUGGING> when you compile the Perl
+executable. This flag is automatically set if you include C<-g>
+option when C<Configure> asks you about optimizer/debugger flags.
=item B<-e> I<commandline>
If B<-e> is given, Perl
will not look for a script filename in the argument list.
Multiple B<-e> commands may
-be given to build up a multiline script.
+be given to build up a multi-line script.
Make sure to use semicolons where you would in a normal program.
=item B<-F>I<pattern>
the selected filehandle. Note that STDOUT is restored as the
default output filehandle after the loop.
-You can use C<eof> without parenthesis to locate the end of each input file,
+You can use C<eof> without parentheses to locate the end of each input file,
in case you want to append to each file, or reset line numbering (see
example in L<perlfunc/eof>).
}
Note that the lines are not printed by default. See B<-p> to have
-lines printed. Here is an efficient way to delete all files older than
-a week:
+lines printed. If a file named by an argument cannot be opened for
+some reason, Perl warns you about it, and moves on to the next file.
+
+Here is an efficient way to delete all files older than a week:
find . -mtime +7 -print | perl -nle 'unlink;'
while (<>) {
... # your script goes here
} continue {
- print;
+ print or die "-p destination: $!\n";
}
-Note that the lines are printed automatically. To suppress printing
-use the B<-n> switch. A B<-p> overrides a B<-n> switch.
+If a file named by an argument cannot be opened for some reason, Perl
+warns you about it, and moves on to the next file. Note that the
+lines are printed automatically. An error occuring during printing is
+treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
+overrides a B<-n> switch.
C<BEGIN> and C<END> blocks may be used to capture control before or after
the implicit loop, just as in awk.
=item B<-S>
makes Perl use the PATH environment variable to search for the
-script (unless the name of the script starts with a slash). Typically
-this is used to emulate #! startup on machines that don't support #!,
-in the following manner:
+script (unless the name of the script contains directory separators).
+On some platforms, this also makes Perl append suffixes to the
+filename while searching for it. For example, on Win32 platforms,
+the ".bat" and ".cmd" suffixes are appended if a lookup for the
+original name fails, and if the name does not already end in one
+of those suffixes. If your Perl was compiled with DEBUGGING turned
+on, using the -Dp switch to Perl shows how the search progresses.
+
+If the filename supplied contains directory separators (i.e. it is an
+absolute or relative pathname), and if the file is not found,
+platforms that append file extensions will do so and try to look
+for the file with those extensions added, one by one.
+
+On DOS-like platforms, if the script does not contain directory
+separators, it will first be searched for in the current directory
+before being searched for on the PATH. On Unix platforms, the
+script will be searched for strictly on the PATH.
+
+Typically this is used to emulate #! startup on platforms that
+don't support #!. This example works on many platforms that
+have a shell compatible with Bourne shell:
#!/usr/bin/perl
- eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
+ eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
The system ignores the first line and feeds the script to /bin/sh,
contain the full pathname, so the B<-S> tells Perl to search for the
script if necessary. After Perl locates the script, it parses the
lines and ignores them because the variable $running_under_some_shell
-is never true. A better construct than C<$*> would be C<${1+"$@"}>, which
-handles embedded spaces and such in the filenames, but doesn't work if
-the script is being interpreted by csh. To start up sh rather
+is never true. If the script will be interpreted by csh, you will need
+to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
+embedded spaces (and such) in the argument list. To start up sh rather
than csh, some systems may have to replace the #! line with a line
containing just a colon, which will be politely ignored by Perl. Other
systems can't control that, and need a totally devious construct that
will work under any of csh, sh, or Perl, such as the following:
- eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
- & eval 'exec /usr/bin/perl -S $0 $argv:q'
+ eval '(exit $?0)' && eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
+ & eval 'exec /usr/bin/perl -wS $0 $argv:q'
if $running_under_some_shell;
=item B<-T>
-forces "taint" checks to be turned on so you can test them. Ordinarily these checks are
-done only when running setuid or setgid. It's a good idea to turn
-them on explicitly for programs run on another's behalf, such as CGI
-programs. See L<perlsec>.
+forces "taint" checks to be turned on so you can test them. Ordinarily
+these checks are done only when running setuid or setgid. It's a good
+idea to turn them on explicitly for programs run on another's behalf,
+such as CGI programs. See L<perlsec>. Note that (for security reasons)
+this option must be seen by Perl quite early; usually this means it must
+appear early on the command line or in the #! line (for systems which
+support that).
=item B<-u>
allows Perl to do unsafe operations. Currently the only "unsafe"
operations are the unlinking of directories while running as superuser,
and running setuid programs with fatal taint checks turned into
-warnings.
+warnings. Note that the B<-w> switch (or the C<$^W> variable) must
+be used along with this option to actually B<generate> the
+taint-check warnings.
=item B<-v>
BEGIN { require 'perl5db.pl' }
+=item PERL5SHELL (specific to WIN32 port)
+
+May be set to an alternative shell that perl must use internally for
+executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
+on WindowsNT and C<command.com /c> on Windows95. The value is considered
+to be space delimited. Precede any character that needs to be protected
+(like a space or backslash) with a backslash.
+
+Note that Perl doesn't use COMSPEC for this purpose because
+COMSPEC has a high degree of variability among users, leading to
+portability concerns. Besides, perl can use a shell that may not be
+fit for interactive use, and setting COMSPEC to such a shell may
+interfere with the proper functioning of other programs (which usually
+look in COMSPEC to find a shell fit for interactive use).
+
=item PERL_DEBUG_MSTATS
-Relevant only if your perl executable was built with B<-DDEBUGGING_MSTATS>,
-if set, this causes memory statistics to be dumped after execution. If set
+Relevant only if perl is compiled with the malloc included with the perl
+distribution (that is, if C<perl -V:d_mymalloc> is 'define').
+If set, this causes memory statistics to be dumped after execution. If set
to an integer greater than one, also causes memory statistics to be dumped
after compilation.
the following lines before doing anything else, just to keep people
honest:
- $ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
- $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
- $ENV{'IFS'} = '' if defined $ENV{'IFS'};
+ $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
+ $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
+ delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
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