PERLRUN(1) Perl Programmers Reference Guide PERLRUN(1)NAMEperlrun - 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[exten_
sion] ] [ -e 'command' ] [ -- ] [ program_
file ] [ 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 follow
ing 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 argu
ments 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 get
ting 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 men
tioned 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 inter
preter, 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 pro
gram named after the #! is executed instead of the Perl
interpreter. This is slightly bizarre, but it helps peo
ple 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 pro
gram 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 asso
ciate 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 = $status = undef;
at the top of your program, where -mysw are any com
mand line switches you want to pass to Perl. You can
now invoke the program directly, by saying "perl pro
gram", or as a DCL procedure, by saying "@program" (or
implicitly via DCL$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:start
perl"".
Command-interpreters on non-Unix systems have rather dif
ferent 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 whites
pace 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 sys
tems. 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 func
tionality 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 char
acters 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 ("$/") as an
octal number. If there are no digits, the null char
acter is the separator. Other switches may precede
or follow the digits. For example, if you have a
version of find which can print filenames terminated
by the null character, you can say this:
find . -name '*.orig' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files
in paragraph mode. The value 0777 will cause Perl to
slurp files whole because there is no legal character
with that value.
-a turns on autosplit mode when used with a -n or -p.
An implicit split command to the @F array is done as
the first thing inside the implicit while loop pro
duced by the -n or -p.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using -F.
-C enables Perl to use the native wide character APIs on
the target system. The magic variable "${^WIDE_SYS
TEM_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 execu
tion of your program. "INIT" and "END" blocks, how
ever, 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 dis
plays compiled regular expressions. As an alterna
tive, 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 argu
ment list. Multiple -e commands may be given to
build up a multi-line script. Make sure to use semi
colons 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 origi
nal 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 suf
fix. If the extension does contain one or more "*"
characters, then each "*" is replaced with the cur
rent 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 file
handle. 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 perl
faq5 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 argu
ments 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 mis
handling newlines in pathnames, which you can fix if
you
"BEGIN" and "END" blocks may be used to capture con
trol 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 argu
ments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
If a file named by an argument cannot be opened for
some reason, Perl warns you about it, and moves on to
the next file. Note that the lines are printed auto
matically. An error occurring during printing is
treated as fatal. To suppress printing use the -n
switch. A -p overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture con
trol before or after the implicit loop, just as in
awk.
-P causes your program to be run through the C prepro
cessor before compilation by Perl. Because both com
ments and cpp directives begin with the # character,
you should avoid starting comments with any words
recognized by the C preprocessor such as ""if"",
""else"", or ""define"". Also, in some platforms the
C preprocessor knows too much: it knows about the C++
-style until-end-of-line comments starting with
""//"". This will cause problems with common Perl
constructs like
s/foo//;
because after -P this will became illegal code
s/foo
The workaround is to use some other quoting separator
than ""/"", like for example ""!"":
s!foo!!;
-s enables rudimentary switch parsing for switches on
the command line after the program name but before
any filename arguments (or before an argument of --).
This means you can have switches with two leading
dashes (--help). Any switch found there is removed
from @ARGV and sets the corresponding variable in the
Perl program. The following program prints "1" if
the program is invoked with a -xyz switch, and "abc"
if it is invoked with -xyz=abc.
#!/usr/bin/perl -s
if ($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 pro
gram contains directory separators).
On some platforms, this also makes Perl append suf
fixes 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 plat
forms 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 pro
gram 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 $run
ning_under_some_shell is never true. If the program
will be interpreted by csh, you will need to replace
"${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 contain
ing 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 separa
tors (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 con
tain 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 direc
tories while running as superuser, and running setuid
programs with fatal taint checks turned into warn
ings. Note that the -w switch (or the "$^W" vari
able) must be used along with this option to actually
generate the taint-check warnings.
-v prints the version and patchlevel of your perl exe
cutable.
-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 file
handles 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 "^$W"
variable. You can disable or promote into fatal
errors specific warnings using "__WARN__" hooks, as
described in the perlvar manpage and the warn entry
in the perlfunc manpage. See also the perldiag man
page and the perltrap manpage. A new, fine-grained
warning facility is also available if you want to
manipulate entire classes of warnings; see the warn
ings manpage or the perllexwarn manpage.
-W Enables all warnings regardless of "no warnings" or
"$^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 mes
sage. 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 direc
tory. Any architecture-specific directories
under the specified locations are automati
cally 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 subse
quent 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 direc
tory. 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 back
slash) 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 portabil
ity 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 statis
tics to be dumped after execution. If set to
an integer greater than one, also causes mem
ory 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 vari
ables, except to make them available to the program being
executed, and to child processes. However, programs run
ning 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)};
2001-03-18 perl v5.6.1 PERLRUN(1)
