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PERLRUN(1)
NAME
perlrun - how to execute the Perl interpreter
SYNOPSIS
perl [ -sTtuUWX ] [ -hv ] [ -V[:configvar] ]
[ -cw ] [ -d[t][:debugger] ] [ -D[number/list] ]
[ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal/hexadecimal] ]
[ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -P ]
[ -S ] [ -x[dir] ] [ -i[extension] ]
[ -e 'command' ] [ -- ] [ programfile ] [ argument ]...
[ -C [number/list] ] ]>
DESCRIPTION
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
perldebug for details on how to do that.) Upon startup, Perl looks for your
program in one of the following places:
1. Specified line by line via -e switches on the command line.
2. Contained in the file specified by the first filename on the command
line. (Note that systems supporting the #! notation invoke
interpreters this way. See "Location of Perl".)
3. Passed in implicitly via standard input. This works only if there are
no filename arguments--to pass arguments to a STDIN-read program you
must explicitly specify a "-" for the program name.
With methods 2 and 3, Perl starts parsing the input file from the
beginning, unless you've specified a -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 program embedded in a larger
message. (In this case you would indicate the end of the program using the
"__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 -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 -I switch could also cause odd results.
Some switches do care if they are processed twice, for instance
combinations of -l and -0. Either put all the switches after the
32-character boundary (if applicable), or replace the use of -0digits by
"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 perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
to let Perl see the -p switch.
A similar trick involves the 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
dispatch the program to the correct interpreter for them.
After locating your program, Perl compiles the entire program to an
internal form. If there are any compilation errors, execution of the
program is not attempted. (This is unlike the typical shell script, which
might run part-way through before finding a syntax error.)
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
exit(0) is provided to indicate successful completion.
#! and quoting on non-Unix systems
Unix's #! technique can be simulated on other systems:
OS/2
Put
extproc perl -S -your_switches
as the first line in "*.cmd" file (-S due to a bug in cmd.exe's
`extproc' handling).
MS-DOS
Create a batch file to run your program, and codify it in
"ALTERNATE_SHEBANG" (see the dosish.h file in the source distribution
for more information).
Win95/NT
The Win95/NT installation, when using the ActiveState installer for
Perl, will modify the Registry to associate the .pl extension with the
perl interpreter. If you install Perl by other means (including
building from the sources), you may have to 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.
Macintosh
Under "Classic" MacOS, a perl program will have the appropriate Creator
and Type, so that double-clicking them will invoke the MacPerl
application. Under Mac OS X, clickable apps can be made from any "#!"
script using Wil Sanchez' DropScript utility:
http://www.wsanchez.net/software/ .
VMS Put
$ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
$ exit++ + ++$status != 0 and $exit = $status = undef;
at the top of your program, where -mysw are any command line switches
you want to pass to Perl. You can now invoke the program directly, by
saying "perl program", or as a DCL procedure, by saying @program (or
implicitly via DCL$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 "perl "-V:startperl"".
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 ("*", "\" and """ are common) and how to protect
whitespace and these characters to run one-liners (see -e below).
On some systems, you may have to change single-quotes to double ones, which
you must not do on Unix or Plan 9 systems. You might also have to change a
single % to a %%.
For example:
# Unix
perl -e 'print "Hello world\n"'
# MS-DOS, etc.
perl -e "print \"Hello world\n\""
# Macintosh
print "Hello world\n"
(then Run "Myscript" or Shift-Command-R)
# 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 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 when
nobody was looking, but just try to find documentation for its quoting
rules.
Under the Macintosh, it depends which environment you are using. The
MacPerl shell, or MPW, is much like Unix shells in its support for several
quoting variants, except that it makes free use of the Macintosh's non-
ASCII characters as control characters.
There is no general solution to all of this. It's just a mess.
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 /usr/bin/perl and
/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, "#!/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:
use 5.005_54;
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:
-0[octal/hexadecimal]
specifies the input record separator ($/) as an octal or hexadecimal
number. If there are no digits, the null character is the separator.
Other switches may precede or follow the digits. For example, if you
have a version of find which can print filenames terminated by the
null character, you can say this:
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 legal byte with that value.
If you want to specify any Unicode character, use the hexadecimal
format: "-0xHHH...", where the "H" are valid hexadecimal digits.
(This means that you cannot use the "-x" with a directory name that
consists of hexadecimal digits.)
-a turns on autosplit mode when used with a -n or -p. An implicit split
command to the @F array is done as the first thing inside the implicit
while loop produced by the -n or -p.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using -F.
-C [number/list]
The "-C" flag controls some Unicode of the Perl Unicode features.
As of 5.8.1, the "-C" can be followed either by a number or a list of
option letters. The letters, their numeric values, and effects are as
follows; listing the letters is equal to summing the numbers.
I 1 STDIN is assumed to be in UTF-8
O 2 STDOUT will be in UTF-8
E 4 STDERR will be in UTF-8
S 7 I + O + E
i 8 UTF-8 is the default PerlIO layer for input streams
o 16 UTF-8 is the default PerlIO layer for output streams
D 24 i + o
A 32 the @ARGV elements are expected to be strings encoded in UTF-8
L 64 normally the "IOEioA" are unconditional,
the L makes them conditional on the locale environment
variables (the LC_ALL, LC_TYPE, and LANG, in the order
of decreasing precedence) -- if the variables indicate
UTF-8, then the selected "IOEioA" are in effect
For example, "-COE" and "-C6" will both turn on UTF-8-ness on both
STDOUT and STDERR. Repeating letters is just redundant, not
cumulative nor toggling.
The "io" options mean that any subsequent open() (or similar I/O
operations) will have the ":utf8" PerlIO layer implicitly applied to
them, in other words, UTF-8 is expected from any input stream, and
UTF-8 is produced to any output stream. This is just the default,
with explicit layers in open() and with binmode() one can manipulate
streams as usual.
"-C" on its own (not followed by any number or option list), or the
empty string "" for the "PERL_UNICODE" environment variable, has the
same effect as "-CSDL". In other words, the standard I/O handles and
the default "open()" layer are UTF-8-fied but only if the locale
environment variables indicate a UTF-8 locale. This behaviour follows
the implicit (and problematic) UTF-8 behaviour of Perl 5.8.0.
You can use "-C0" (or "0" for "PERL_UNICODE") to explicitly disable
all the above Unicode features.
The read-only magic variable "${^UNICODE}" reflects the numeric value
of this setting. This is variable is set during Perl startup and is
thereafter read-only. If you want runtime effects, use the three-arg
open() (see "open" in perlfunc), the two-arg binmode() (see "binmode"
in perlfunc), and the "open" pragma (see open).
(In Perls earlier than 5.8.1 the "-C" switch was a Win32-only switch
that enabled the use of Unicode-aware "wide system call" Win32 APIs.
This feature was practically unused, however, and the command line
switch was therefore "recycled".)
-c causes Perl to check the syntax of the program and then exit without
executing it. Actually, it will execute "BEGIN", "CHECK", and "use"
blocks, because these are considered as occurring outside the
execution of your program. "INIT" and "END" blocks, however, will be
skipped.
-d
-dt runs the program under the Perl debugger. See perldebug. If t is
specified, it indicates to the debugger that threads will be used in
the code being debugged.
-d:foo[=bar,baz]
-dt:foo[=bar,baz]
runs the program under the control of a debugging, profiling, or
tracing module installed as Devel::foo. E.g., -d:DProf executes the
program using the Devel::DProf profiler. As with the -M flag, options
may be passed to the Devel::foo package where they will be received
and interpreted by the Devel::foo::import routine. The comma-
separated list of options must follow a "=" character. If t is
specified, it indicates to the debugger that threads will be used in
the code being debugged. See perldebug.
-Dletters
-Dnumber
sets debugging flags. To watch how it executes your program, use
-Dtls. (This works only if debugging is compiled into your Perl.)
Another nice value is -Dx, which lists your compiled syntax tree. And
-Dr displays compiled regular expressions; the format of the output is
explained in perldebguts.
As an alternative, specify a number instead of list of letters (e.g.,
-D14 is equivalent to -Dtls):
1 p Tokenizing and parsing
2 s Stack snapshots (with v, displays all stacks)
4 l Context (loop) stack processing
8 t Trace execution
16 o Method and overloading resolution
32 c String/numeric conversions
64 P Print profiling info, preprocessor command for -P, source file input state
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 (Obsolete, previously used for LEAKTEST)
8192 H Hash dump -- usurps values()
16384 X Scratchpad allocation
32768 D Cleaning up
65536 S Thread synchronization
131072 T Tokenising
262144 R Include reference counts of dumped variables (eg when using -Ds)
524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
1048576 v Verbose: use in conjunction with other flags
8388608 q quiet - currently only suppresses the "EXECUTING" message
All these flags require -DDEBUGGING when you compile the Perl
executable (but see Devel::Peek, re which may change this). See the
INSTALL file in the Perl source distribution for how to do this. This
flag is automatically set if you include -g option when "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 "sh -x" provides for shell scripts, you
can't use Perl's -D switch. Instead do this
# If you have "env" utility
env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
# 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 perldebug for details and variations.
-e commandline
may be used to enter one line of program. If -e is given, Perl will
not look for a filename in the argument list. Multiple -e commands
may be given to build up a multi-line script. Make sure to use
semicolons where you would in a normal program.
-f Disable executing $Config{siteperl}/sitecustomize.pl at startup.
Perl can be built so that it by default will try to execute
$Config{siteperl}/sitecustomize.pl at startup. This is a hook that
allows the sysadmin to customize how perl behaves. It can for
instance be used to add entries to the @INC array to make perl find
modules in non-standard locations.
-Fpattern
specifies the pattern to split on if -a is also in effect. The
pattern may be surrounded by "//", "", or '', otherwise it will be put
in single quotes.
-h prints a summary of the options.
-i[extension]
specifies that files processed by the "<>" construct are to be edited
in-place. It does this by renaming the input file, opening the output
file by the original name, and selecting that output file as the
default for print() statements. The extension, if supplied, is used
to modify the name of the old file to make a backup copy, following
these rules:
If no extension is supplied, no backup is made and the current file is
overwritten.
If the extension doesn't contain a "*", then it is appended to the end
of the current filename as a suffix. If the extension does contain
one or more "*" characters, then each "*" is replaced with the current
filename. In Perl terms, you could think of this as:
($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'
From the shell, saying
$ perl -p -i.orig -e "s/foo/bar/; ... "
is the same as using the program:
#!/usr/bin/perl -pi.orig
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
$extension = '.orig';
LINE: while (<>) {
if ($ARGV ne $oldargv) {
if ($extension !~ /\*/) {
$backup = $ARGV . $extension;
}
else {
($backup = $extension) =~ s/\*/$ARGV/g;
}
rename($ARGV, $backup);
open(ARGVOUT, ">$ARGV");
select(ARGVOUT);
$oldargv = $ARGV;
}
s/foo/bar/;
}
continue {
print; # this prints to original filename
}
select(STDOUT);
except that the -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.
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 "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 "eof" in perlfunc).
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 -i, see
"Why does Perl let me delete read-only files? Why does -i clobber
protected files? Isn't this a bug in Perl?" in perlfaq5.
You cannot use -i to create directories or to strip extensions from
files.
Perl does not expand "~" in filenames, which is good, since some folks
use it for their backup files:
$ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
Note that because -i renames or deletes the original file before
creating a new file of the same name, UNIX-style soft and hard links
will not be preserved.
Finally, the -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.
-Idirectory
Directories specified by -I are prepended to the search path for
modules (@INC), and also tells the C preprocessor where to search for
include files. The C preprocessor is invoked with -P; by default it
searches /usr/include and /usr/lib/perl.
-l[octnum]
enables automatic line-ending processing. It has two separate
effects. First, it automatically chomps $/ (the input record
separator) when used with -n or -p. Second, it assigns "$\" (the
output record separator) to have the value of octnum so that any print
statements will have that separator added back on. If octnum is
omitted, sets "$\" to the current value of $/. For instance, to trim
lines to 80 columns:
perl -lpe 'substr($_, 80) = ""'
Note that the assignment "$\ = $/" is done when the switch is
processed, so the input record separator can be different than the
output record separator if the -l switch is followed by a -0 switch:
gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
This sets "$\" to newline and then sets $/ to the null character.
-m[-]module
-M[-]module
-M[-]'module ...'
-[mM][-]module=arg[,arg]...
-mmodule executes "use" module "();" before executing your program.
-Mmodule executes "use" module ";" before executing your program. You
can use quotes to add extra code after the module name, e.g.,
'-Mmodule qw(foo bar)'.
If the first character after the -M or -m is a dash ("-") then the
'use' is replaced with 'no'.
A little builtin syntactic sugar means you can also say
-mmodule=foo,bar or -Mmodule=foo,bar as a shortcut for '-Mmodule
qw(foo bar)'. This avoids the need to use quotes when importing
symbols. The actual code generated by -Mmodule=foo,bar is "use module
split(/,/,q{foo,bar})". Note that the "=" form removes the
distinction between -m and -M.
-n causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like sed -n or awk:
LINE:
while (<>) {
... # your program goes here
}
Note that the lines are not printed by default. See -p to have 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 that haven't been
modified for at least a week:
find . -mtime +7 -print | perl -nle unlink
This is faster than using the -exec switch of 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
follow the example under -0.
"BEGIN" and "END" blocks may be used to capture control before or
after the implicit program loop, just as in awk.
-p causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
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 -n switch. A -p
overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture control before or
after the implicit loop, just as in awk.
-P NOTE: Use of -P is strongly discouraged because of its inherent
problems, including poor portability.
This option causes your program to be run through the C preprocessor
before compilation by Perl. Because both comments and 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".
If you're considering using "-P", you might also want to look at the
Filter::cpp module from CPAN.
The problems of -P include, but are not limited to:
* The "#!" line is stripped, so any switches there don't
apply.
* A "-P" on a "#!" line doesn't work.
* All lines that begin with (whitespace and) a "#" but do not
look like cpp commands, are stripped, including anything
inside Perl strings, regular expressions, and here-docs .
* In some platforms the C preprocessor knows too much: it
knows about the C++ -style until-end-of-line comments
starting with "//". This will cause problems with common
Perl constructs like
s/foo//;
because after -P this will became illegal code
s/foo
The workaround is to use some other quoting separator than
"/", like for example "!":
s!foo!!;
* It requires not only a working C preprocessor but also a
working sed. If not on UNIX, you are probably out of luck
on this.
* Script line numbers are not preserved.
* The "-x" does not work with "-P".
-s enables rudimentary switch parsing for switches on the command line
after the program name but before any filename arguments (or before an
argument of --). This means you can have switches with two leading
dashes (--help). Any switch found there is removed from @ARGV and
sets the corresponding variable in the Perl program. The following
program prints "1" if the program is invoked with a -xyz switch, and
"abc" if it is invoked with -xyz=abc.
#!/usr/bin/perl -s
if ($xyz) { print "$xyz\n" }
Do note that --help creates the variable ${-help}, which is not
compliant with "strict refs". Also, when using this option on a
script with warnings enabled you may get a lot of spurious "used only
once" warnings.
-S makes Perl use the PATH environment variable to search for the 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 #!. Its also convenient when debugging a script that uses #!,
and is thus normally found by the shell's $PATH search mechanism.
This example works on many platforms that have a shell compatible with
Bourne shell:
#!/usr/bin/perl
eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
The system ignores the first line and feeds the program to /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 -S tells Perl to search for the
program if necessary. After Perl locates the program, it parses the
lines and ignores them because the variable $running_under_some_shell
is never true. If the program will be interpreted by csh, you will
need to replace "${1+"$@"}" with $*, 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 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.
-t Like -T, but taint checks will issue warnings rather than fatal
errors. These warnings can be controlled normally with "no warnings
qw(taint)".
NOTE: this is not a substitute for -T. This is meant only to be used
as a temporary development aid while securing legacy code: for real
production code and for new secure code written from scratch always
use the real -T.
-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 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
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.
-u 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 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 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 B and B::Bytecode for
details.
-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. Note that the -w switch (or the $^W variable) must be
used along with this option to actually generate the taint-check
warnings.
-v prints the version and patchlevel of your perl executable.
-V prints summary of the major perl configuration values and the current
values of @INC.
-V:configvar
Prints to STDOUT the value of the named configuration variable(s),
with multiples when your configvar argument looks like a regex (has
non-letters). For example:
$ perl -V:libc
libc='/lib/libc-2.2.4.so';
$ perl -V:lib.
libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
libc='/lib/libc-2.2.4.so';
$ perl -V:lib.*
libpth='/usr/local/lib /lib /usr/lib';
libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
lib_ext='.a';
libc='/lib/libc-2.2.4.so';
libperl='libperl.a';
....
Additionally, extra colons can be used to control formatting. A
trailing colon suppresses the linefeed and terminator ';', allowing
you to embed queries into shell commands. (mnemonic: PATH separator
':'.)
$ echo "compression-vars: " `perl -V:z.*: ` " are here !"
compression-vars: zcat='' zip='zip' are here !
A leading colon removes the 'name=' part of the response, this allows
you to map to the name you need. (mnemonic: empty label)
$ echo "goodvfork="`./perl -Ilib -V::usevfork`
goodvfork=false;
Leading and trailing colons can be used together if you need
positional parameter values without the names. Note that in the case
below, the PERL_API params are returned in alphabetical order.
$ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
building_on 'linux' '5' '1' '9' now
-w 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 don'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 $^W variable. You can
disable or promote into fatal errors specific warnings using
"__WARN__" hooks, as described in perlvar and "warn" in perlfunc. See
also perldiag and perltrap. A new, fine-grained warning facility is
also available if you want to manipulate entire classes of warnings;
see warnings or perllexwarn.
-W Enables all warnings regardless of "no warnings" or $^W. See
perllexwarn.
-X Disables all warnings regardless of "use warnings" or $^W. See
perllexwarn.
-x
-x directory
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 -x switch controls only the disposal
of leading garbage. The program must be terminated with "__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).
ENVIRONMENT
HOME Used if chdir has no argument.
LOGDIR Used if chdir has no argument and HOME is not set.
PATH Used in executing subprocesses, and in finding the program if
-S is used.
PERL5LIB A list of directories in which to look for Perl library files
before looking in the standard library and the current
directory. Any architecture-specific directories under the
specified locations are automatically included if they exist.
If PERL5LIB is not defined, PERLLIB is used. Directories are
separated (like in PATH) by a colon on unixish platforms and by
a semicolon on Windows (the proper path separator being given
by the command "perl -V:path_sep").
When running taint checks (either because the program was
running setuid or setgid, or the -T switch was used), neither
variable is used. The program should instead say:
use lib "/my/directory";
PERL5OPT Command-line options (switches). Switches in this variable are
taken as if they were on every Perl command line. Only the
-[DIMUdmtw] switches are allowed. When running taint checks
(because the program was running setuid or setgid, or the -T
switch was used), this variable is ignored. If PERL5OPT begins
with -T, tainting will be enabled, and any subsequent options
ignored.
PERLIO A space (or colon) separated list of PerlIO layers. If perl is
built to use PerlIO system for IO (the default) these layers
effect perl's IO.
It is conventional to start layer names with a colon e.g.
":perlio" to emphasise their similarity to variable
"attributes". But the code that parses layer specification
strings (which is also used to decode the PERLIO environment
variable) treats the colon as a separator.
An unset or empty PERLIO is equivalent to ":stdio".
The list becomes the default for all perl's IO. Consequently
only built-in layers can appear in this list, as external
layers (such as :encoding()) need IO in order to load them!.
See "open pragma" for how to add external encodings as
defaults.
The layers that it makes sense to include in the PERLIO
environment variable are briefly summarised below. For more
details see PerlIO.
:bytes A pseudolayer that turns off the ":utf8" flag for the
layer below. Unlikely to be useful on its own in the
global PERLIO environment variable. You perhaps were
thinking of ":crlf:bytes" or ":perlio:bytes".
:crlf A layer which does CRLF to "\n" translation
distinguishing "text" and "binary" files in the manner
of MS-DOS and similar operating systems. (It currently
does not mimic MS-DOS as far as treating of Control-Z
as being an end-of-file marker.)
:mmap A layer which implements "reading" of files by using
"mmap()" to make (whole) file appear in the process's
address space, and then using that as PerlIO's
"buffer".
:perlio This is a re-implementation of "stdio-like" buffering
written as a PerlIO "layer". As such it will call
whatever layer is below it for its operations
(typically ":unix").
:pop An experimental pseudolayer that removes the topmost
layer. Use with the same care as is reserved for
nitroglycerin.
:raw A pseudolayer that manipulates other layers. Applying
the ":raw" layer is equivalent to calling
"binmode($fh)". It makes the stream pass each byte
as-is without any translation. In particular CRLF
translation, and/or :utf8 intuited from locale are
disabled.
Unlike in the earlier versions of Perl ":raw" is not
just the inverse of ":crlf" - other layers which would
affect the binary nature of the stream are also removed
or disabled.
:stdio This layer provides PerlIO interface by wrapping
system's ANSI C "stdio" library calls. The layer
provides both buffering and IO. Note that ":stdio"
layer does not do CRLF translation even if that is
platforms normal behaviour. You will need a ":crlf"
layer above it to do that.
:unix Low level layer which calls "read", "write" and "lseek"
etc.
:utf8 A pseudolayer that turns on a flag on the layer below
to tell perl that output should be in utf8 and that
input should be regarded as already in utf8 form. May
be useful in PERLIO environment variable to make UTF-8
the default. (To turn off that behaviour use ":bytes"
layer.)
:win32 On Win32 platforms this experimental layer uses native
"handle" IO rather than unix-like numeric file
descriptor layer. Known to be buggy in this release.
On all platforms the default set of layers should give
acceptable results.
For UNIX platforms that will equivalent of "unix perlio" or
"stdio". Configure is setup to prefer "stdio" implementation
if system's library provides for fast access to the buffer,
otherwise it uses the "unix perlio" implementation.
On Win32 the default in this release is "unix crlf". Win32's
"stdio" has a number of bugs/mis-features for perl IO which are
somewhat C compiler vendor/version dependent. Using our own
"crlf" layer as the buffer avoids those issues and makes things
more uniform. The "crlf" layer provides CRLF to/from "\n"
conversion as well as buffering.
This release uses "unix" as the bottom layer on Win32 and so
still uses C compiler's numeric file descriptor routines. There
is an experimental native "win32" layer which is expected to be
enhanced and should eventually be the default under Win32.
PERLIO_DEBUG
If set to the name of a file or device then certain operations
of PerlIO sub-system will be logged to that file (opened as
append). Typical uses are UNIX:
PERLIO_DEBUG=/dev/tty perl script ...
and Win32 approximate equivalent:
set PERLIO_DEBUG=CON
perl script ...
This functionality is disabled for setuid scripts and for
scripts run with -T.
PERLLIB A list of directories in which to look for Perl library files
before looking in the standard library and the current
directory. If PERL5LIB is defined, PERLLIB is not used.
PERL5DB The command used to load the debugger code. The default is:
BEGIN { require 'perl5db.pl' }
PERL5DB_THREADED
If set to a true value, indicates to the debugger that the code
being debugged uses threads.
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 "cmd.exe /x/d/c" on WindowsNT and "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).
PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
Set to 1 to allow the use of non-IFS compatible LSP's. Perl
normally searches for an IFS-compatible LSP because this is
required for its emulation of Windows sockets as real
filehandles. However, this may cause problems if you have a
firewall such as McAfee Guardian which requires all
applications to use its LSP which is not IFS-compatible,
because clearly Perl will normally avoid using such an LSP.
Setting this environment variable to 1 means that Perl will
simply use the first suitable LSP enumerated in the catalog,
which keeps McAfee Guardian happy (and in that particular case
Perl still works too because McAfee Guardian's LSP actually
plays some other games which allow applications requiring IFS
compatibility to work).
PERL_DEBUG_MSTATS
Relevant only if perl is compiled with the malloc included with
the perl distribution (that is, if "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.
PERL_DESTRUCT_LEVEL
Relevant only if your perl executable was built with
-DDEBUGGING, this controls the behavior of global destruction
of objects and other references. See "PERL_DESTRUCT_LEVEL" in
perlhack for more information.
PERL_DL_NONLAZY
Set to one to have perl resolve all undefined symbols when it
loads a dynamic library. The default behaviour is to resolve
symbols when they are used. Setting this variable is useful
during testing of extensions as it ensures that you get an
error on misspelled function names even if the test suite
doesn't call it.
PERL_ENCODING
If using the "encoding" pragma without an explicit encoding
name, the PERL_ENCODING environment variable is consulted for
an encoding name.
PERL_HASH_SEED
(Since Perl 5.8.1.) Used to randomise Perl's internal hash
function. To emulate the pre-5.8.1 behaviour, set to an
integer (zero means exactly the same order as 5.8.0).
"Pre-5.8.1" means, among other things, that hash keys will be
ordered the same between different runs of Perl.
The default behaviour is to randomise unless the PERL_HASH_SEED
is set. If Perl has been compiled with
"-DUSE_HASH_SEED_EXPLICIT", the default behaviour is not to
randomise unless the PERL_HASH_SEED is set.
If PERL_HASH_SEED is unset or set to a non-numeric string, Perl
uses the pseudorandom seed supplied by the operating system and
libraries. This means that each different run of Perl will
have a different ordering of the results of keys(), values(),
and each().
Please note that the hash seed is sensitive information. Hashes
are randomized to protect against local and remote attacks
against Perl code. By manually setting a seed this protection
may be partially or completely lost.
See "Algorithmic Complexity Attacks" in perlsec and
"PERL_HASH_SEED_DEBUG" for more information.
PERL_HASH_SEED_DEBUG
(Since Perl 5.8.1.) Set to one to display (to STDERR) the
value of the hash seed at the beginning of execution. This,
combined with "PERL_HASH_SEED" is intended to aid in debugging
nondeterministic behavior caused by hash randomization.
Note that the hash seed is sensitive information: by knowing it
one can craft a denial-of-service attack against Perl code,
even remotely, see "Algorithmic Complexity Attacks" in perlsec
for more information. Do not disclose the hash seed to people
who don't need to know it. See also hash_seed() of Hash::Util.
PERL_ROOT (specific to the VMS port)
A translation concealed rooted logical name that contains perl
and the logical device for the @INC path on VMS only. Other
logical names that affect perl on VMS include PERLSHR,
PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL but are optional
and discussed further in perlvms and in README.vms in the Perl
source distribution.
PERL_SIGNALS
In Perls 5.8.1 and later. If set to "unsafe" the
pre-Perl-5.8.0 signals behaviour (immediate but unsafe) is
restored. If set to "safe" the safe (or deferred) signals are
used. See "Deferred Signals (Safe Signals)" in perlipc.
PERL_UNICODE
Equivalent to the -C command-line switch. Note that this is
not a boolean variable-- setting this to "1" is not the right
way to "enable Unicode" (whatever that would mean). You can
use "0" to "disable Unicode", though (or alternatively unset
PERL_UNICODE in your shell before starting Perl). See the
description of the "-C" switch for more information.
SYS$LOGIN (specific to the VMS port)
Used if chdir has no argument and HOME and LOGDIR are not set.
Perl also has environment variables that control how Perl handles data
specific to particular natural languages. See perllocale.
Apart from these, Perl uses no other environment variables, except 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 exists $ENV{SHELL};
delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
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