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PERLRUN(1)
NAME
perlrun - how to execute the Perl interpreter
SYNOPSIS
perl [ -CsTuUWX ] [ -hv ] [ -V[:configvar] ]
[ -cw ] [ -d[:debugger] ] [ -D[number/list] ]
[ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal] ]
[ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -P ]
[ -S ] [ -x[dir] ] [ -i[extension] ]
[ -e 'command' ] [ -- ] [ programfile ] [ argument ]...
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 the
perldebug manpage 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 the Location of Perl entry elsewhere in this
document.)
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
"ALTERNATIVE_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
A Macintosh perl program will have the appropriate Creator and Type, so
that double-clicking them will invoke the perl application.
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 Plan9 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[digits]
specifies the input record separator ("$/") as an octal number. If
there are no digits, the null character is the separator. Other
switches may precede or follow the digits. For example, if you have a
version of find which can print filenames terminated by the null
character, you can say this:
find . -name '*.orig' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in paragraph mode.
The value 0777 will cause Perl to slurp files whole because there is
no legal character with that value.
-a turns on autosplit mode when used with a -n or -p. An implicit split
command to the @F array is done as the first thing inside the implicit
while loop produced by the -n or -p.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using -F.
-C enables Perl to use the native wide character APIs on the target
system. The magic variable "${^WIDE_SYSTEM_CALLS}" reflects the state
of this switch. See the section on "${^WIDE_SYSTEM_CALLS}" in the
perlvar manpage.
This feature is currently only implemented on the Win32 platform.
-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 runs the program under the Perl debugger. See the perldebug manpage.
-d: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. See the
perldebug manpage.
-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. 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
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, 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 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
131072 T Tokenising
All these flags require -DDEBUGGING when you compile the Perl
executable. 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
# 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 the perldebug manpage 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.
-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 the eof entry in the perlfunc manpage).
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
the Why does Perl let me delete read-only files? Why does -i clobber
protected files? Isn't this a bug in Perl? entry in the perlfaq5
manpage.
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...
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 older than 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
"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: $!\n";
}
If a file named by an argument cannot be opened for some reason, Perl
warns you about it, and moves on to the next file. Note that the
lines are printed automatically. An error occurring during printing
is treated as fatal. To suppress printing use the -n switch. A -p
overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture control before or
after the implicit loop, just as in awk.
-P causes your program to be run through the C preprocessor before
compilation by Perl. Because both comments and cpp directives begin
with the # character, you should avoid starting comments with any
words recognized by the C preprocessor such as ""if"", ""else"", or
""define"". Also, in some platforms the C preprocessor knows too
much: it knows about the C++ -style until-end-of-line comments
starting with ""//"". This will cause problems with common Perl
constructs like
s/foo//;
because after -P this will became illegal code
s/foo
The workaround is to use some other quoting separator than ""/"", like
for example ""!"":
s!foo!!;
-s enables rudimentary switch parsing for switches on the command line
after the program name but before any filename arguments (or before an
argument of --). This means you can have switches with two leading
dashes (--help). Any switch found there is removed from @ARGV and
sets the corresponding variable in the Perl program. The following
program prints "1" if the program is invoked with a -xyz switch, and
"abc" if it is invoked with -xyz=abc.
#!/usr/bin/perl -s
if ($xyz) { print "$xyz\n" }
Do note that --help creates the variable ${-help}, which is not
compliant with "strict refs".
-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 #!. 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 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 the
perlsec manpage 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 the B manpage and the
B::Bytecode manpage 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: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.
-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 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 "^$W" variable. You can
disable or promote into fatal errors specific warnings using
"__WARN__" hooks, as described in the perlvar manpage and the warn
entry in the perlfunc manpage. See also the perldiag manpage and the
perltrap manpage. A new, fine-grained warning facility is also
available if you want to manipulate entire classes of warnings; see
the warnings manpage or the perllexwarn manpage.
-W Enables all warnings regardless of "no warnings" or "$^W". See the
perllexwarn manpage.
-X Disables all warnings regardless of "use warnings" or "$^W". See the
perllexwarn manpage.
-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 colon-separated 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.
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
-[DIMUdmw] 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.
PERLLIB 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 defined, PERLLIB is not
used.
PERL5DB The command used to load the debugger code. The default is:
BEGIN { require 'perl5db.pl' }
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/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_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.
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 the perlvms manpage and in README.vms
in the Perl source distribution.
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 the perllocale manpage.
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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