=head1 SYNOPSIS
-B<perl> S<[ B<-sTuU> ]>
+B<perl> S<[ B<-sTuUWX> ]>
S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
=head1 DESCRIPTION
-Upon startup, Perl looks for your script in one of the following
+The normal way to run a Perl program is by making it directly
+executable, or else by passing the name of the source file as an
+argument on the command line. (An interactive Perl environment
+is also possible--see L<perldebug> for details on how to do that.)
+Upon startup, Perl looks for your program in one of the following
places:
=over 4
=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.
Passed in implicitly via standard input. This works only if there are
-no filename arguments--to pass arguments to a STDIN script you
-must explicitly specify a "-" for the script name.
+no filename arguments--to pass arguments to a STDIN-read program you
+must explicitly specify a "-" for the program name.
=back
With methods 2 and 3, Perl starts parsing the input file from the
beginning, unless you've specified a B<-x> switch, in which case it
scans for the first line starting with #! and containing the word
-"perl", and starts there instead. This is useful for running a script
+"perl", and starts there instead. This is useful for running a program
embedded in a larger message. (In this case you would indicate the end
-of the script using the C<__END__> token.)
+of the program using the C<__END__> token.)
The #! line is always examined for switches as the line is being
parsed. Thus, if you're on a machine that allows only one argument
with the #! line, or worse, doesn't even recognize the #! line, you
still can get consistent switch behavior regardless of how Perl was
-invoked, even if B<-x> was used to find the beginning of the script.
-
-Because many operating systems silently chop off kernel interpretation of
-the #! line after 32 characters, some switches may be passed in on the
-command line, and some may not; you could even get a "-" without its
-letter, if you're not careful. You probably want to make sure that all
-your switches fall either before or after that 32 character boundary.
-Most switches don't actually care if they're processed redundantly, but
-getting a - instead of a complete switch could cause Perl to try to
-execute standard input instead of your script. And a partial B<-I> switch
+invoked, even if B<-x> was used to find the beginning of the program.
+
+Because historically some operating systems silently chopped off
+kernel interpretation of the #! line after 32 characters, some
+switches may be passed in on the command line, and some may not;
+you could even get a "-" without its letter, if you're not careful.
+You probably want to make sure that all your switches fall either
+before or after that 32-character boundary. Most switches don't
+actually care if they're processed redundantly, but getting a "-"
+instead of a complete switch could cause Perl to try to execute
+standard input instead of your program. 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 perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
-to let Perl see the B<-p> switch.
+to let Perl see the B<-p> switch.
+
+A similar trick involves the B<env> program, if you have it.
+
+ #!/usr/bin/env perl
+
+The examples above use a relative path to the perl interpreter,
+getting whatever version is first in the user's path. If you want
+a specific version of Perl, say, perl5.005_57, you should place
+that directly in the #! line's path.
If the #! line does not contain the word "perl", the program named after
the #! is executed instead of the Perl interpreter. This is slightly
bizarre, but it helps people on machines that don't do #!, because they
-can tell a program that their SHELL is /usr/bin/perl, and Perl will then
+can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
dispatch the program to the correct interpreter for them.
-After locating your script, Perl compiles the entire script to an
+After locating your program, Perl compiles the entire program to an
internal form. If there are any compilation errors, execution of the
-script is not attempted. (This is unlike the typical shell script,
+program is not attempted. (This is unlike the typical shell script,
which might run part-way through before finding a syntax error.)
-If the script is syntactically correct, it is executed. If the script
+If the program is syntactically correct, it is executed. If the program
runs off the end without hitting an exit() or die() operator, an implicit
C<exit(0)> is provided to indicate successful completion.
extproc perl -S -your_switches
-as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
+as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
`extproc' handling).
=item MS-DOS
-Create a batch file to run your script, and codify it in
+Create a batch file to run your program, and codify it in
C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
distribution for more information).
=item Win95/NT
The Win95/NT installation, when using the Activeware port of Perl,
-will modify the Registry to associate the .pl extension with the perl
+will modify the Registry to associate the F<.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
-modify the Registry yourself.
+modify the Registry yourself. Note that this means you can no
+longer tell the difference between an executable Perl program
+and a Perl library file.
=item Macintosh
-Macintosh perl scripts will have the the appropriate Creator and
+A Macintosh perl program will have the appropriate Creator and
Type, so that double-clicking them will invoke the perl application.
+=item VMS
+
+Put
+
+ $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
+ $ exit++ + ++$status != 0 and $exit = $status = undef;
+
+at the top of your program, where B<-mysw> are any command line switches you
+want to pass to Perl. You can now invoke the program directly, by saying
+C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
+via F<DCL$PATH> by just using the name of the program).
+
+This incantation is a bit much to remember, but Perl will display it for
+you if you say C<perl "-V:startperl">.
+
=back
Command-interpreters on non-Unix systems have rather different ideas
on quoting than Unix shells. You'll need to learn the special
characters in your command-interpreter (C<*>, C<\> and C<"> are
common) and how to protect whitespace and these characters to run
-one-liners (see C<-e> below).
+one-liners (see B<-e> below).
On some systems, you may have to change single-quotes to double ones,
-which you must I<NOT> do on Unix or Plan9 systems. You might also
+which you must I<not> do on Unix or Plan9 systems. You might also
have to change a single % to a %%.
For example:
# VMS
perl -e "print ""Hello world\n"""
-The problem is that none of this is reliable: it depends on the command
-and it is entirely possible neither works. If 4DOS was the command shell, this would
-probably work better:
+The problem is that none of this is reliable: it depends on the
+command and it is entirely possible neither works. If B<4DOS> were
+the command shell, this would probably work better:
perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
-CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
+B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
when nobody was looking, but just try to find documentation for its
quoting rules.
There is no general solution to all of this. It's just a mess.
-=head2 Switches
+=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 F</usr/bin/perl>
+and F</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 into a
+directory typically found along a user's PATH, or in some other
+obvious and convenient place.
+
+In this documentation, C<#!/usr/bin/perl> on the first line of the program
+will stand in for whatever method works on your system. You are
+advised to use a specific path if you care about a specific version.
+
+ #!/usr/local/bin/perl5.00554
+
+or if you just want to be running at least version, place a statement
+like this at the top of your program:
-A single-character switch may be combined with the following switch, if
-any.
+ use 5.005_54;
- #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
+=head2 Command Switches
+
+As with all standard commands, a single-character switch may be
+clustered with the following switch, if any.
+
+ #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
Switches include:
B<find> which can print filenames terminated by the null character, you
can say this:
- find . -name '*.bak' -print0 | perl -n0e unlink
+ find . -name '*.orig' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in paragraph mode.
The value 0777 will cause Perl to slurp files whole because there is no
=item B<-c>
-causes Perl to check the syntax of the script and then exit without
+causes Perl to check the syntax of the program and then exit without
executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
because these are considered as occurring outside the execution of
-your program.
+your program. C<INIT> blocks, however, will be skipped.
=item B<-d>
-runs the
script under the Perl debugger. See L<perldebug>.
+runs the
program under the Perl debugger. See L<perldebug>.
=item B<-d:>I<foo>
-runs the script under the control of a debugging or tracing module
-installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
-Devel::DProf profiler. See L<perldebug>.
+runs the program under the control of a debugging, profiling, or
+tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
+
the program 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
+sets debugging flags. To watch how it executes your program, use
+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 -DLEAKTEST when compiling Perl)
+ 8192 H Hash dump -- usurps values()
+ 16384 X Scratchpad allocation
+ 32768 D Cleaning up
+ 65536 S Thread synchronization
+
+All these flags require B<-DDEBUGGING> when you compile the Perl
+executable. See the F<INSTALL> file in the Perl source distribution
+for how to do this. This flag is automatically set if you include B<-g>
+option when C<Configure> asks you about optimizer/debugger flags.
+
+If you're just trying to get a print out of each line of Perl code
+as it executes, the way that C<sh -x> provides for shell scripts,
+you can't use Perl's B<-D> switch. Instead do this
+
+ # Bourne shell syntax
+ $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
+
+ # csh syntax
+ % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
+
+See L<perldebug> for details and variations.
=item B<-e> I<commandline>
-may be used to enter one line of script.
-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 multi-line script.
-Make sure to use semicolons where you would in a normal program.
+may be used to enter one line of program. If B<-e> is given, Perl
+will not look for a filename in the argument list. Multiple B<-e>
+commands may 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>
=item B<-i>[I<extension>]
-specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
-in-place. It does this by renaming the input file, opening the output
-file by the original name, and selecting that output file as the default
-for print() statements. The extension, if supplied, is added to the name
-of the old file to make a backup copy. If no extension is supplied, no
-backup is made. From the shell, saying
+specifies that files processed by the C<E<lt>E<gt>> construct are to be
+edited in-place. It does this by renaming the input file, opening the
+output file by the original name, and selecting that output file as the
+default for print() statements. The extension, if supplied, is used to
+modify the name of the old file to make a backup copy, following these
+rules:
+
+If no extension is supplied, no backup is made and the current file is
+overwritten.
+
+If the extension doesn't contain a C<*>, then it is appended to the
+end of the current filename as a suffix. If the extension does
+contain one or more C<*> characters, then each C<*> is replaced
+with the current filename. In Perl terms, you could think of this
+as:
+
+ ($backup = $extension) =~ s/\*/$file_name/g;
+
+This allows you to add a prefix to the backup file, instead of (or in
+addition to) a suffix:
+
+ $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
+
+Or even to place backup copies of the original files into another
+directory (provided the directory already exists):
+
+ $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
+
+These sets of one-liners are equivalent:
+
+ $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
+ $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
+
+ $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
+ $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
- $ perl -p -i.bak -e "s/foo/bar/; ... "
+From the shell, saying
-is the same as using the script:
+ $ perl -p -i.orig -e "s/foo/bar/; ... "
- #!/usr/bin/perl -pi.bak
+is the same as using the program:
+
+ #!/usr/bin/perl -pi.orig
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
- while (<>) {
+ $extension = '.orig';
+ LINE: while (<>) {
if ($ARGV ne $oldargv) {
- rename($ARGV, $ARGV . '.bak');
+ if ($extension !~ /\*/) {
+ $backup = $ARGV . $extension;
+ }
+ else {
+ ($backup = $extension) =~ s/\*/$ARGV/g;
+ }
+ rename($ARGV, $backup);
open(ARGVOUT, ">$ARGV");
select(ARGVOUT);
$oldargv = $ARGV;
except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
know when the filename has changed. It does, however, use ARGVOUT for
-the selected filehandle. Note that STDOUT is restored as the
-default output filehandle after the loop.
+the selected filehandle. Note that STDOUT is restored as the default
+output filehandle after the loop.
+
+As shown above, Perl creates the backup file whether or not any output
+is actually changed. So this is just a fancy way to copy files:
+
+ $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3...
+or
+ $ perl -p -i '.orig' -e 1 file1 file2 file3...
+
+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>).
+
+If, for a given file, Perl is unable to create the backup file as
+specified in the extension then it will skip that file and continue on
+with the next one (if it exists).
+
+For a discussion of issues surrounding file permissions and B<-i>,
+see L<perlfaq5/Why does Perl let me delete read-only files? Why
+does -i clobber protected files? Isn't this a bug in Perl?>.
-You can use C<eof> without parenthesis 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>).
+You cannot use B<-i> to create directories or to strip extensions from
+files.
+
+Perl does not expand C<~> in filenames, which is good, since some
+folks use it for their backup files:
+
+ $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
+
+Finally, the B<-i> switch does not impede execution when no
+files are given on the command line. In this case, no backup is made
+(the original file cannot, of course, be determined) and processing
+proceeds from STDIN to STDOUT as might be expected.
=item B<-I>I<directory>
=item B<-l>[I<octnum>]
-enables automatic line-ending processing. It has two effects: first,
-it automatically chomps "C<$/>" (the input record separator) when used
-with B<-n> or B<-p>, and second, it assigns "C<$\>"
-(the output record separator) to have the value of I<octnum> so that
-any print statements will have that separator added back on. If
-I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
-instance, to trim lines to 80 columns:
+enables automatic line-ending processing. It has two separate
+effects. First, it automatically chomps C<$/> (the input record
+separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
+(the output record separator) to have the value of I<octnum> so
+that any print statements will have that separator added back on.
+If I<octnum> is omitted, sets C<$\> to the current value of
+C<$/>. For instance, to trim lines to 80 columns:
perl -lpe 'substr($_, 80) = ""'
=item B<-[mM]>[B<->]I<module=arg[,arg]...>
-C<-m>I<module> executes C<use> I<module> C<();> before executing your
-script.
+B<-m>I<module> executes C<use> I<module> C<();> before executing your
+program.
-C<-M>I<module> executes C<use> I<module> C<;> before executing your
-script. You can use quotes to add extra code after the module name,
-e.g., C<-M'module qw(foo bar)'>.
+B<-M>I<module> executes C<use> I<module> C<;> before executing your
+program. You can use quotes to add extra code after the module name,
+e.g., C<'-Mmodule qw(foo bar)'>.
-If the first character after the C<-M> or C<-m> is a dash (C<->)
+If the first character after the B<-M> or B<-m> is a dash (C<->)
then the 'use' is replaced with 'no'.
A little builtin syntactic sugar means you can also say
-C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
-C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
-importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
+B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
+C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
+importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
-removes the distinction between C<-m> and C<-M>.
+removes the distinction between B<-m> and B<-M>.
=item B<-n>
-causes Perl to assume the following loop around your script, which
+causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like B<sed -n> or
B<awk>:
+ LINE:
while (<>) {
- ... # your script goes here
+ ... # your program goes here
}
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;'
+ find . -mtime +7 -print | perl -nle unlink
-This is faster than using the C<-exec> switch of B<find> because you don't
-have to start a process on every filename found.
+This is faster than using the B<-exec> switch of B<find> because you don't
+have to start a process on every filename found. It does suffer from
+the bug of mishandling newlines in pathnames, which you can fix if
+you
C<BEGIN> and C<END> blocks may be used to capture control before or after
-the implicit loop, just as in B<awk>.
+the implicit
program loop, just as in B<awk>.
=item B<-p>
-causes Perl to assume the following loop around your script, which
+causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like B<sed>:
+ LINE:
while (<>) {
- ... # your script goes here
+ ... # your program goes here
} continue {
- print;
+ print or die "-p destination: $!\n";
}
-Note that the lines are printed automatically. To suppress printing
-use the B<-n> switch. A B<-p> overrides a B<-n> switch.
+If a file named by an argument cannot be opened for some reason, Perl
+warns you about it, and moves on to the next file. Note that the
+lines are printed automatically. An error occurring during printing is
+treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
+overrides a B<-n> switch.
C<BEGIN> and C<END> blocks may be used to capture control before or after
-the implicit loop, just as in awk.
+the implicit loop, just as in B<awk>.
=item B<-P>
-causes your script to be run through the C preprocessor before
-compilation by Perl. (Because both comments and cpp directives begin
+causes your program to be run through the C preprocessor before
+compilation by Perl. (Because both comments and B<cpp> directives begin
with the # character, you should avoid starting comments with any words
recognized by the C preprocessor such as "if", "else", or "define".)
=item B<-s>
-enables some rudimentary switch parsing for switches on the command
-line after the script name but before any filename arguments (or before
+enables rudimentary switch parsing for switches on the command
+line after the program name but before any filename arguments (or before
a B<-->). Any switch found there is removed from @ARGV and sets the
-corresponding variable in the Perl script. The following script
-prints "true" if and only if the script is invoked with a B<-xyz> switch.
+corresponding variable in the Perl program. The following program
+prints "true" if and only if the program is invoked with a B<-xyz> switch.
#!/usr/bin/perl -s
- if ($xyz) { print "true\n"; }
+ if ($xyz) { print "true\n" }
=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:
+program (unless the name of the program 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.
+
+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,
-which proceeds to try to execute the Perl script as a shell script.
+The system ignores the first line and feeds the program to F</bin/sh>,
+which proceeds to try to execute the Perl program as a shell script.
The shell executes the second line as a normal shell command, and thus
starts up the Perl interpreter. On some systems $0 doesn't always
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
+program if necessary. After Perl locates the program, 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 program 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:
+will work under any of B<csh>, B<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 perl -wS $0 ${1+"$@"}'
+ & eval 'exec /usr/bin/perl -wS $0 $argv:q'
if $running_under_some_shell;
+If the filename supplied contains directory separators (i.e., is an
+absolute or relative pathname), and if that 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 program 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
+program will be searched for strictly on the PATH.
+
=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 that run on behalf
+of someone else whom you might not necessarily trust, such as CGI
+programs or any internet servers you might write in Perl. See
+L<perlsec> for details. 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 construct.
=item B<-u>
-causes Perl to dump core after compiling your script. You can then
-take this core dump and turn it into an executable file by using the
-B<undump> program (not supplied). This speeds startup at the expense of
-some disk space (which you can minimize by stripping the executable).
-(Still, a "hello world" executable comes out to about 200K on my
-machine.) If you want to execute a portion of your script before dumping,
-use the dump() operator instead. Note: availability of B<undump> is
-platform specific and may not be available for a specific port of
-Perl.
+This obsolete switch causes Perl to dump core after compiling your
+program. You can then in theory take this core dump and turn it
+into an executable file by using the B<undump> program (not supplied).
+This speeds startup at the expense of some disk space (which you
+can minimize by stripping the executable). (Still, a "hello world"
+executable comes out to about 200K on my machine.) If you want to
+execute a portion of your program before dumping, use the dump()
+operator instead. Note: availability of B<undump> is platform
+specific and may not be available for a specific port of Perl.
+
+This switch has been superseded in favor of the new Perl code
+generator backends to the compiler. See L<B> and L<B::Bytecode>
+for details.
=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 I<generate> the
+taint-check warnings.
=item B<-v>
-prints the version and patchlevel of your Perl executable.
+prints the version and patchlevel of your perl executable.
=item B<-V>
prints summary of the major perl configuration values and the current
-value of @INC.
+values of @INC.
=item B<-V:>I<name>
Prints to STDOUT the value of the named configuration variable.
+For example,
+
+ $ perl -V:man.dir
+
+will provide strong clues about what your MANPATH variable should
+be set to in order to access the Perl documentation.
=item B<-w>
-prints warnings about variable names that are mentioned only once, and
-scalar variables that are used before being set. Also warns about
-redefined subroutines, and references to undefined filehandles or
-filehandles opened read-only that you are attempting to write on. Also
-warns you if you use values as a number that doesn't look like numbers,
-using an array as though it were a scalar, if your subroutines recurse
-more than 100 deep, and innumerable other things.
+prints warnings about dubious constructs, such as variable names
+that are mentioned only once and scalar variables that are used
+before being set, redefined subroutines, references to undefined
+filehandles or filehandles opened read-only that you are attempting
+to write on, values used as a number that doesn't look like numbers,
+using an array as though it were a scalar, if your subroutines
+recurse more than 100 deep, and innumerable other things.
+
+This switch really just enables the internal C<^$W> variable. You
+can disable or promote into fatal errors specific warnings using
+C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
+See also L<perldiag> and L<perltrap>. A new, fine-grained warning
+facility is also available if you want to manipulate entire classes
+of warnings; see L<warning> (or better yet, its source code) about
+that.
-You can disable specific warnings using C<__WARN__> hooks, as described
-in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>.
+=item B<-W>
+
+Enables all warnings regardless of
+See L<perllexwarn>.
+
+=item B<-X>
+
+Disables all warnings regardless of
+See L<perllexwarn>.
=item B<-x> I<directory>
-tells Perl that the script is embedded in a message. Leading
-garbage will be discarded until the first line that starts with #! and
-contains the string "perl". Any meaningful switches on that line will
-be applied. If a directory name is specified, Perl will switch to
-that directory before running the script. The B<-x> switch controls
-only the disposal of leading garbage. The script must be
-terminated with C<__END__> if there is trailing garbage to be ignored (the
-script can process any or all of the trailing garbage via the DATA
-filehandle if desired).
+tells Perl that the program is embedded in a larger chunk of unrelated
+ASCII text, such as in a mail message. Leading garbage will be
+discarded until the first line that starts with #! and contains the
+string "perl". Any meaningful switches on that line will be applied.
+If a directory name is specified, Perl will switch to that directory
+before running the program. The B<-x> switch controls only the
+disposal of leading garbage. The program must be terminated with
+C<__END__> if there is trailing garbage to be ignored (the program
+can process any or all of the trailing garbage via the DATA filehandle
+if desired).
=back
=item PATH
-Used in executing subprocesses, and in finding the script if B<-S> is
+Used in executing subprocesses, and in finding the program if B<-S> is
used.
=item PERL5LIB
A colon-separated list of directories in which to look for Perl library
files before looking in the standard library and the current
directory. If PERL5LIB is not defined, PERLLIB is used. When running
-taint checks (because the script was running setuid or setgid, or the
-B<-T> switch was used), neither variable is used. The script should
+taint checks (because the program was running setuid or setgid, or the
+B<-T> switch was used), neither variable is used. The program should
instead say
use lib "/my/directory";
Command-line options (switches). Switches in this variable are taken
as if they were on every Perl command line. Only the B<-[DIMUdmw]>
-switches are allowed. When running taint checks (because the script
+switches are allowed. When running taint checks (because the program
was running setuid or setgid, or the B<-T> switch was used), this
-variable is ignored.
+variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
+enabled, and any subsequent options ignored.
=item PERLLIB
BEGIN { require 'perl5db.pl' }
+=item PERL5SHELL (specific to the 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-separated. 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.
specific to particular natural languages. See L<perllocale>.
Apart from these, Perl uses no other environment variables, except
-to make them available to the script being executed, and to child
-processes. However, scripts running setuid would do well to execute
+to make them available to the program being executed, and to child
+processes. However, programs running setuid would do well to execute
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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