X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlrun.pod;h=f1e2c9a62ecb7e530a1ad62ea606e342f866fef0;hb=9f1b1f2d9ab55954ee07a14c4ab04bd3dd1f99d5;hp=df606bf0eabb75f43d65415419519613341595cf;hpb=ff0cee690d2ef6ba882e59dd4baaa0c944adb7a2;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlrun.pod b/pod/perlrun.pod index df606bf..f1e2c9a 100644 --- a/pod/perlrun.pod +++ b/pod/perlrun.pod @@ -4,7 +4,7 @@ perlrun - how to execute the Perl interpreter =head1 SYNOPSIS -B S<[ B<-sTuU> ]> +B S<[ B<-CsTuUWX> ]> S<[ B<-hv> ] [ B<-V>[:I] ]> S<[ B<-cw> ] [ B<-d>[:I] ] [ B<-D>[I] ]> S<[ B<-pna> ] [ B<-F>I ] [ B<-l>[I] ] [ B<-0>[I] ]> @@ -17,7 +17,11 @@ B S<[ B<-sTuU> ]> =head1 DESCRIPTION -Upon startup, Perl looks for your script in one of the following +The normal way to run a Perl program is by making it directly +executable, or else by passing the name of the source file as an +argument on the command line. (An interactive Perl environment +is also possible--see L for details on how to do that.) +Upon startup, Perl looks for your program in one of the following places: =over 4 @@ -29,70 +33,201 @@ Specified line by line via B<-e> switches on the command line. =item 2. Contained in the file specified by the first filename on the command line. -(Note that systems supporting the #! notation invoke interpreters this way.) +(Note that systems supporting the #! notation invoke interpreters this +way. See L.) =item 3. Passed in implicitly via standard input. This works only if there are -no filename arguments--to pass arguments to a STDIN script you -must explicitly specify a "-" for the script name. +no filename arguments--to pass arguments to a STDIN-read program you +must explicitly specify a "-" for the program name. =back With methods 2 and 3, Perl starts parsing the input file from the beginning, unless you've specified a B<-x> switch, in which case it scans for the first line starting with #! and containing the word -"perl", and starts there instead. This is useful for running a script +"perl", and starts there instead. This is useful for running a program embedded in a larger message. (In this case you would indicate the end -of the script using the __END__ token.) +of the program using the C<__END__> token.) The #! line is always examined for switches as the line is being parsed. Thus, if you're on a machine that allows only one argument with the #! line, or worse, doesn't even recognize the #! line, you still can get consistent switch behavior regardless of how Perl was -invoked, even if B<-x> was used to find the beginning of the script. - -Because many operating systems silently chop off kernel interpretation of -the #! line after 32 characters, some switches may be passed in on the -command line, and some may not; you could even get a "-" without its -letter, if you're not careful. You probably want to make sure that all -your switches fall either before or after that 32 character boundary. -Most switches don't actually care if they're processed redundantly, but -getting a - instead of a complete switch could cause Perl to try to -execute standard input instead of your script. And a partial B<-I> switch +invoked, even if B<-x> was used to find the beginning of the program. + +Because historically some operating systems silently chopped off +kernel interpretation of the #! line after 32 characters, some +switches may be passed in on the command line, and some may not; +you could even get a "-" without its letter, if you're not careful. +You probably want to make sure that all your switches fall either +before or after that 32-character boundary. Most switches don't +actually care if they're processed redundantly, but getting a "-" +instead of a complete switch could cause Perl to try to execute +standard input instead of your program. And a partial B<-I> switch could also cause odd results. +Some switches do care if they are processed twice, for instance +combinations of B<-l> and B<-0>. Either put all the switches after +the 32-character boundary (if applicable), or replace the use of +B<-0>I by C. + Parsing of the #! switches starts wherever "perl" is mentioned in the line. The sequences "-*" and "- " are specifically ignored so that you could, if you were so inclined, say #!/bin/sh -- # -*- perl -*- -p - eval 'exec /usr/bin/perl $0 -S ${1+"$@"}' + eval 'exec perl -wS $0 ${1+"$@"}' if $running_under_some_shell; -to let Perl see the B<-p> switch. +to let Perl see the B<-p> switch. + +A similar trick involves the B program, if you have it. + + #!/usr/bin/env perl + +The examples above use a relative path to the perl interpreter, +getting whatever version is first in the user's path. If you want +a specific version of Perl, say, perl5.005_57, you should place +that directly in the #! line's path. If the #! line does not contain the word "perl", the program named after the #! is executed instead of the Perl interpreter. This is slightly bizarre, but it helps people on machines that don't do #!, because they -can tell a program that their SHELL is /usr/bin/perl, and Perl will then +can tell a program that their SHELL is F, and Perl will then dispatch the program to the correct interpreter for them. -After locating your script, Perl compiles the entire script to an +After locating your program, Perl compiles the entire program to an internal form. If there are any compilation errors, execution of the -script is not attempted. (This is unlike the typical shell script, -which might run partway through before finding a syntax error.) +program is not attempted. (This is unlike the typical shell script, +which might run part-way through before finding a syntax error.) -If the script is syntactically correct, it is executed. If the script +If the program is syntactically correct, it is executed. If the program runs off the end without hitting an exit() or die() operator, an implicit C is provided to indicate successful completion. -=head2 Switches +=head2 #! and quoting on non-Unix systems + +Unix's #! technique can be simulated on other systems: + +=over 4 + +=item OS/2 + +Put + + extproc perl -S -your_switches + +as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's +`extproc' handling). + +=item MS-DOS + +Create a batch file to run your program, and codify it in +C (see the F file in the source +distribution for more information). + +=item Win95/NT + +The Win95/NT installation, when using the ActiveState installer for Perl, +will modify the Registry to associate the F<.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. + +=item Macintosh + +A Macintosh perl program will have the appropriate Creator and +Type, so that double-clicking them will invoke the perl application. + +=item VMS + +Put + + $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' ! + $ exit++ + ++$status != 0 and $exit = $status = undef; + +at the top of your program, where B<-mysw> are any command line switches you +want to pass to Perl. You can now invoke the program directly, by saying +C, or as a DCL procedure, by saying C<@program> (or implicitly +via F by just using the name of the program). + +This incantation is a bit much to remember, but Perl will display it for +you if you say C. + +=back + +Command-interpreters on non-Unix systems have rather different ideas +on quoting than Unix shells. You'll need to learn the special +characters in your command-interpreter (C<*>, C<\> and C<"> are +common) and how to protect whitespace and these characters to run +one-liners (see B<-e> below). + +On some systems, you may have to change single-quotes to double ones, +which you must I 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"' -A single-character switch may be combined with the following switch, if -any. + # MS-DOS, etc. + perl -e "print \"Hello world\n\"" - #!/usr/bin/perl -spi.bak # same as -s -p -i.bak + # 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 B<4DOS> were +the command shell, this would probably work better: + + perl -e "print "Hello world\n"" + +B 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. + +=head2 Location of Perl + +It may seem obvious to say, but Perl is useful only when users can +easily find it. When possible, it's good for both F +and F to be symlinks to the actual binary. If +that can't be done, system administrators are strongly encouraged +to put (symlinks to) perl and its accompanying utilities into a +directory typically found along a user's PATH, or in some other +obvious and convenient place. + +In this documentation, C<#!/usr/bin/perl> on the first line of the program +will stand in for whatever method works on your system. You are +advised to use a specific path if you care about a specific version. + + #!/usr/local/bin/perl5.00554 + +or if you just want to be running at least version, place a statement +like this at the top of your program: + + use 5.005_54; + +=head2 Command Switches + +As with all standard commands, a single-character switch may be +clustered with the following switch, if any. + + #!/usr/bin/perl -spi.orig # same as -s -p -i.orig Switches include: @@ -106,7 +241,7 @@ precede or follow the digits. For example, if you have a version of B which can print filenames terminated by the null character, you can say this: - find . -name '*.bak' -print0 | perl -n0e unlink + find . -name '*.orig' -print0 | perl -n0e unlink The special value 00 will cause Perl to slurp files in paragraph mode. The value 0777 will cause Perl to slurp files whole because there is no @@ -129,59 +264,84 @@ is equivalent to An alternate delimiter may be specified using B<-F>. +=item B<-C> + +enables Perl to use the native wide character APIs on the target system. +The magic variable C<${^WIDE_SYSTEM_CALLS}> reflects the state of +this switch. See L. + +This feature is currently only implemented on the Win32 platform. + =item B<-c> -causes Perl to check the syntax of the script and then exit without -executing it. Actually, it I execute C, C, and C blocks, -because these are considered as occurring outside the execution of -your program. +causes Perl to check the syntax of the program and then exit without +executing it. Actually, it I execute C, C, and +C blocks, because these are considered as occurring outside the +execution of your program. C and C blocks, however, will +be skipped. =item B<-d> -runs the script under the Perl debugger. See L. +runs the program under the Perl debugger. See L. =item B<-d:>I -runs the script under the control of a debugging or tracing module -installed as Devel::foo. E.g., B<-d:DProf> executes the script using the -Devel::DProf profiler. See L. +runs the program under the control of a debugging, profiling, or +tracing module installed as Devel::foo. E.g., B<-d:DProf> executes +the program using the Devel::DProf profiler. See L. -=item B<-D>I +=item B<-D>I -=item B<-D>I +=item B<-D>I -sets debugging flags. To watch how it executes your script, use -B<-D14>. (This works only if debugging is compiled into your -Perl.) Another nice value is B<-D1024>, which lists your compiled -syntax tree. And B<-D512> displays compiled regular expressions. As an -alternative specify a list of letters instead of numbers (e.g., B<-D14> is +sets debugging flags. To watch how it executes your program, use +B<-Dtls>. (This works only if debugging is compiled into your +Perl.) Another nice value is B<-Dx>, which lists your compiled +syntax tree. And B<-Dr> displays compiled regular expressions. As an +alternative, specify a number instead of list of letters (e.g., B<-D14> is equivalent to B<-Dtls>): - 1 p Tokenizing and Parsing - 2 s Stack Snapshots - 4 l Label Stack Processing - 8 t Trace Execution - 16 o Operator Node Construction - 32 c String/Numeric Conversions - 64 P Print Preprocessor Command for -P - 128 m Memory Allocation - 256 f Format Processing - 512 r Regular Expression Parsing - 1024 x Syntax Tree Dump - 2048 u Tainting Checks - 4096 L Memory Leaks (not supported anymore) - 8192 H Hash Dump -- usurps values() - 16384 X Scratchpad Allocation - 32768 D Cleaning Up + 1 p Tokenizing and parsing + 2 s Stack snapshots + 4 l Context (loop) stack processing + 8 t Trace execution + 16 o Method and overloading resolution + 32 c String/numeric conversions + 64 P Print preprocessor command for -P + 128 m Memory allocation + 256 f Format processing + 512 r Regular expression parsing and execution + 1024 x Syntax tree dump + 2048 u Tainting checks + 4096 L Memory leaks (needs -DLEAKTEST when compiling Perl) + 8192 H Hash dump -- usurps values() + 16384 X Scratchpad allocation + 32768 D Cleaning up + 65536 S Thread synchronization + +All these flags require B<-DDEBUGGING> when you compile the Perl +executable. See the F file in the Perl source distribution +for how to do this. This flag is automatically set if you include B<-g> +option when C asks you about optimizer/debugger flags. + +If you're just trying to get a print out of each line of Perl code +as it executes, the way that C provides for shell scripts, +you can't use Perl's B<-D> switch. Instead do this + + # Bourne shell syntax + $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program + + # csh syntax + % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program) + +See L for details and variations. =item B<-e> I -may be used to enter one line of script. -If B<-e> is given, Perl -will not look for a script filename in the argument list. -Multiple B<-e> commands may -be given to build up a multi-line script. -Make sure to use semicolons where you would in a normal program. +may be used to enter one line of program. If B<-e> is given, Perl +will not look for a filename in the argument list. Multiple B<-e> +commands may be given to build up a multi-line script. Make sure +to use semicolons where you would in a normal program. =item B<-F>I @@ -195,26 +355,64 @@ prints a summary of the options. =item B<-i>[I] -specifies that files processed by the CE> construct are to be edited -in-place. It does this by renaming the input file, opening the output -file by the original name, and selecting that output file as the default -for print() statements. The extension, if supplied, is added to the name -of the old file to make a backup copy. If no extension is supplied, no -backup is made. From the shell, saying +specifies that files processed by the CE> construct are to be +edited in-place. It does this by renaming the input file, opening the +output file by the original name, and selecting that output file as the +default for print() statements. The extension, if supplied, is used to +modify the name of the old file to make a backup copy, following these +rules: + +If no extension is supplied, no backup is made and the current file is +overwritten. + +If the extension doesn't contain a C<*>, then it is appended to the +end of the current filename as a suffix. If the extension does +contain one or more C<*> characters, then each C<*> is replaced +with the current filename. In Perl terms, you could think of this +as: + + ($backup = $extension) =~ s/\*/$file_name/g; + +This allows you to add a prefix to the backup file, instead of (or in +addition to) a suffix: + + $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA' + +Or even to place backup copies of the original files into another +directory (provided the directory already exists): + + $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig' + +These sets of one-liners are equivalent: - $ perl -p -i.bak -e "s/foo/bar/; ... " + $ perl -pi -e 's/bar/baz/' fileA # overwrite current file + $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file -is the same as using the script: + $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' + $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' - #!/usr/bin/perl -pi.bak +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 - while (<>) { + $extension = '.orig'; + LINE: while (<>) { if ($ARGV ne $oldargv) { - rename($ARGV, $ARGV . '.bak'); + if ($extension !~ /\*/) { + $backup = $ARGV . $extension; + } + else { + ($backup = $extension) =~ s/\*/$ARGV/g; + } + rename($ARGV, $backup); open(ARGVOUT, ">$ARGV"); select(ARGVOUT); $oldargv = $ARGV; @@ -228,12 +426,40 @@ which is equivalent to except that the B<-i> form doesn't need to compare $ARGV to $oldargv to know when the filename has changed. It does, however, use ARGVOUT for -the selected filehandle. Note that STDOUT is restored as the -default output filehandle after the loop. +the selected filehandle. Note that STDOUT is restored as the default +output filehandle after the loop. + +As shown above, Perl creates the backup file whether or not any output +is actually changed. So this is just a fancy way to copy files: + + $ perl -p -i '/some/file/path/*' -e 1 file1 file2 file3... +or + $ perl -p -i '.orig' -e 1 file1 file2 file3... + +You can use C without parentheses to locate the end of each input +file, in case you want to append to each file, or reset line numbering +(see example in L). -You can use C without parenthesis to locate the end of each input file, -in case you want to append to each file, or reset line numbering (see -example in L). +If, for a given file, Perl is unable to create the backup file as +specified in the extension then it will skip that file and continue on +with the next one (if it exists). + +For a discussion of issues surrounding file permissions and B<-i>, +see L. + +You cannot use B<-i> to create directories or to strip extensions from +files. + +Perl does not expand C<~> in filenames, which is good, since some +folks use it for their backup files: + + $ perl -pi~ -e 's/foo/bar/' file1 file2 file3... + +Finally, the B<-i> switch does not impede execution when no +files are given on the command line. In this case, no backup is made +(the original file cannot, of course, be determined) and processing +proceeds from STDIN to STDOUT as might be expected. =item B<-I>I @@ -244,13 +470,13 @@ searches /usr/include and /usr/lib/perl. =item B<-l>[I] -enables automatic line-ending processing. It has two effects: first, -it automatically chomps "C<$/>" (the input record separator) when used -with B<-n> or B<-p>, and second, it assigns "C<$\>" -(the output record separator) to have the value of I so that -any print statements will have that separator added back on. If -I is omitted, sets "C<$\>" to the current value of "C<$/>". For -instance, to trim lines to 80 columns: +enables automatic line-ending processing. It has two separate +effects. First, it automatically chomps C<$/> (the input record +separator) when used with B<-n> or B<-p>. Second, it assigns C<$\> +(the output record separator) to have the value of I so +that any print statements will have that separator added back on. +If I is omitted, sets C<$\> to the current value of +C<$/>. For instance, to trim lines to 80 columns: perl -lpe 'substr($_, 80) = ""' @@ -270,174 +496,330 @@ This sets C<$\> to newline and then sets C<$/> to the null character. =item B<-[mM]>[B<->]I -C<-m>I executes C I C<();> before executing your -script. +B<-m>I executes C I C<();> before executing your +program. -C<-M>I executes C I C<;> before executing your -script. You can use quotes to add extra code after the module name, -e.g., C<-M'module qw(foo bar)'>. +B<-M>I executes C I C<;> before executing your +program. You can use quotes to add extra code after the module name, +e.g., C<'-Mmodule qw(foo bar)'>. -If the first character after the C<-M> or C<-m> is a dash (C<->) +If the first character after the B<-M> or B<-m> is a dash (C<->) then the 'use' is replaced with 'no'. -A little built-in syntactic sugar means you can also say -C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for -C<-M'module qw(foo bar)'>. This avoids the need to use quotes when -importing symbols. The actual code generated by C<-Mmodule=foo,bar> is +A little builtin syntactic sugar means you can also say +B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for +C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when +importing symbols. The actual code generated by B<-Mmodule=foo,bar> is C. Note that the C<=> form -removes the distinction between C<-m> and C<-M>. +removes the distinction between B<-m> and B<-M>. =item B<-n> -causes Perl to assume the following loop around your script, which +causes Perl to assume the following loop around your program, which makes it iterate over filename arguments somewhat like B or B: + LINE: while (<>) { - ... # your script goes here + ... # your program goes here } Note that the lines are not printed by default. See B<-p> to have -lines printed. Here is an efficient way to delete all files older than -a week: +lines printed. If a file named by an argument cannot be opened for +some reason, Perl warns you about it and moves on to the next file. + +Here is an efficient way to delete all files older than a week: - find . -mtime +7 -print | perl -nle 'unlink;' + find . -mtime +7 -print | perl -nle unlink -This is faster than using the C<-exec> switch of B because you don't -have to start a process on every filename found. +This is faster than using the B<-exec> switch of B because you don't +have to start a process on every filename found. It does suffer from +the bug of mishandling newlines in pathnames, which you can fix if +you C and C blocks may be used to capture control before or after -the implicit loop, just as in B. +the implicit program loop, just as in B. =item B<-p> -causes Perl to assume the following loop around your script, which +causes Perl to assume the following loop around your program, which makes it iterate over filename arguments somewhat like B: + LINE: while (<>) { - ... # your script goes here + ... # your program goes here } continue { - print; + print or die "-p destination: $!\n"; } -Note that the lines are printed automatically. To suppress printing -use the B<-n> switch. A B<-p> overrides a B<-n> switch. +If a file named by an argument cannot be opened for some reason, Perl +warns you about it, and moves on to the next file. Note that the +lines are printed automatically. An error occurring during printing is +treated as fatal. To suppress printing use the B<-n> switch. A B<-p> +overrides a B<-n> switch. C and C blocks may be used to capture control before or after -the implicit loop, just as in awk. +the implicit loop, just as in B. =item B<-P> -causes your script to be run through the C preprocessor before -compilation by Perl. (Because both comments and cpp directives begin +causes your program to be run through the C preprocessor before +compilation by Perl. (Because both comments and B directives begin with the # character, you should avoid starting comments with any words recognized by the C preprocessor such as "if", "else", or "define".) =item B<-s> -enables some rudimentary switch parsing for switches on the command -line after the script name but before any filename arguments (or before +enables rudimentary switch parsing for switches on the command +line after the program name but before any filename arguments (or before a B<-->). Any switch found there is removed from @ARGV and sets the -corresponding variable in the Perl script. The following script -prints "true" if and only if the script is invoked with a B<-xyz> switch. +corresponding variable in the Perl program. The following program +prints "1" if the program is invoked with a B<-xyz> switch, and "abc" +if it is invoked with B<-xyz=abc>. #!/usr/bin/perl -s - if ($xyz) { print "true\n"; } + if ($xyz) { print "$xyz\n" } =item B<-S> makes Perl use the PATH environment variable to search for the -script (unless the name of the script starts with a slash). Typically -this is used to emulate #! startup on machines that don't support #!, -in the following manner: +program (unless the name of the program contains directory separators). + +On some platforms, this also makes Perl append suffixes to the +filename while searching for it. For example, on Win32 platforms, +the ".bat" and ".cmd" suffixes are appended if a lookup for the +original name fails, and if the name does not already end in one +of those suffixes. If your Perl was compiled with DEBUGGING turned +on, using the -Dp switch to Perl shows how the search progresses. + +Typically this is used to emulate #! startup on platforms that +don't support #!. This example works on many platforms that +have a shell compatible with Bourne shell: #!/usr/bin/perl - eval 'exec /usr/bin/perl -S $0 ${1+"$@"}' + eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}' if $running_under_some_shell; -The system ignores the first line and feeds the script to /bin/sh, -which proceeds to try to execute the Perl script as a shell script. +The system ignores the first line and feeds the program to F, +which proceeds to try to execute the Perl program as a shell script. The shell executes the second line as a normal shell command, and thus starts up the Perl interpreter. On some systems $0 doesn't always contain the full pathname, so the B<-S> tells Perl to search for the -script if necessary. After Perl locates the script, it parses the +program if necessary. After Perl locates the program, it parses the lines and ignores them because the variable $running_under_some_shell -is never true. A better construct than C<$*> would be C<${1+"$@"}>, which -handles embedded spaces and such in the filenames, but doesn't work if -the script is being interpreted by csh. To start up sh rather +is never true. If the program will be interpreted by csh, you will need +to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand +embedded spaces (and such) in the argument list. To start up sh rather than csh, some systems may have to replace the #! line with a line containing just a colon, which will be politely ignored by Perl. Other systems can't control that, and need a totally devious construct that -will work under any of csh, sh, or Perl, such as the following: +will work under any of B, B, or Perl, such as the following: - eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}' - & eval 'exec /usr/bin/perl -S $0 $argv:q' + eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}' + & eval 'exec /usr/bin/perl -wS $0 $argv:q' if $running_under_some_shell; +If the filename supplied contains directory separators (i.e., is an +absolute or relative pathname), and if that file is not found, +platforms that append file extensions will do so and try to look +for the file with those extensions added, one by one. + +On DOS-like platforms, if the program does not contain directory +separators, it will first be searched for in the current directory +before being searched for on the PATH. On Unix platforms, the +program will be searched for strictly on the PATH. + =item B<-T> -forces "taint" checks to be turned on so you can test them. Ordinarily these checks are -done only when running setuid or setgid. It's a good idea to turn -them on explicitly for programs run on another's behalf, such as CGI -programs. See L. +forces "taint" checks to be turned on so you can test them. Ordinarily +these checks are done only when running setuid or setgid. It's a +good idea to turn them on explicitly for programs that run on behalf +of someone else whom you might not necessarily trust, such as CGI +programs or any internet servers you might write in Perl. See +L for details. For security reasons, this option must be +seen by Perl quite early; usually this means it must appear early +on the command line or in the #! line for systems which support +that construct. =item B<-u> -causes Perl to dump core after compiling your script. You can then -take this core dump and turn it into an executable file by using the -B program (not supplied). This speeds startup at the expense of -some disk space (which you can minimize by stripping the executable). -(Still, a "hello world" executable comes out to about 200K on my -machine.) If you want to execute a portion of your script before dumping, -use the dump() operator instead. Note: availability of B is -platform specific and may not be available for a specific port of -Perl. +This obsolete switch causes Perl to dump core after compiling your +program. You can then in theory take this core dump and turn it +into an executable file by using the B program (not supplied). +This speeds startup at the expense of some disk space (which you +can minimize by stripping the executable). (Still, a "hello world" +executable comes out to about 200K on my machine.) If you want to +execute a portion of your program before dumping, use the dump() +operator instead. Note: availability of B is platform +specific and may not be available for a specific port of Perl. + +This switch has been superseded in favor of the new Perl code +generator backends to the compiler. See L and L +for details. =item B<-U> allows Perl to do unsafe operations. Currently the only "unsafe" operations are the unlinking of directories while running as superuser, and running setuid programs with fatal taint checks turned into -warnings. +warnings. Note that the B<-w> switch (or the C<$^W> variable) must +be used along with this option to actually I the +taint-check warnings. =item B<-v> -prints the version and patchlevel of your Perl executable. +prints the version and patchlevel of your perl executable. =item B<-V> prints summary of the major perl configuration values and the current -value of @INC. +values of @INC. =item B<-V:>I Prints to STDOUT the value of the named configuration variable. +For example, + + $ perl -V:man.dir + +will provide strong clues about what your MANPATH variable should +be set to in order to access the Perl documentation. =item B<-w> -prints warnings about variable names that are mentioned only once, and -scalar variables that are used before being set. Also warns about -redefined subroutines, and references to undefined filehandles or -filehandles opened read-only that you are attempting to write on. Also -warns you if you use values as a number that doesn't look like numbers, -using an array as though it were a scalar, if your subroutines recurse -more than 100 deep, and innumerable other things. +prints warnings about dubious constructs, such as variable names +that are mentioned only once and scalar variables that are used +before being set, redefined subroutines, references to undefined +filehandles or filehandles opened read-only that you are attempting +to write on, values used as a number that doesn't look like numbers, +using an array as though it were a scalar, if your subroutines +recurse more than 100 deep, and innumerable other things. + +This switch really just enables the internal C<^$W> variable. You +can disable or promote into fatal errors specific warnings using +C<__WARN__> hooks, as described in L and L. +See also L and L. A new, fine-grained warning +facility is also available if you want to manipulate entire classes +of warnings; see L or L. + +=item B<-W> + +Enables all warnings regardless of C or C<$^W>. +See L. -You can disable specific warnings using C<__WARN__> hooks, as described -in L and L. See also L and L. +=item B<-X> + +Disables all warnings regardless of C or C<$^W>. +See L. =item B<-x> I -tells Perl that the script is embedded in a message. Leading -garbage will be discarded until the first line that starts with #! and -contains the string "perl". Any meaningful switches on that line will -be applied. If a directory name is specified, Perl will switch to -that directory before running the script. The B<-x> switch controls -only the disposal of leading garbage. The script must be -terminated with C<__END__> if there is trailing garbage to be ignored (the -script can process any or all of the trailing garbage via the DATA -filehandle if desired). +tells Perl that the program is embedded in a larger chunk of unrelated +ASCII text, such as in a mail message. Leading garbage will be +discarded until the first line that starts with #! and contains the +string "perl". Any meaningful switches on that line will be applied. +If a directory name is specified, Perl will switch to that directory +before running the program. The B<-x> switch controls only the +disposal of leading garbage. The program must be terminated with +C<__END__> if there is trailing garbage to be ignored (the program +can process any or all of the trailing garbage via the DATA filehandle +if desired). + +=back + +=head1 ENVIRONMENT + +=over 12 + +=item HOME + +Used if chdir has no argument. + +=item LOGDIR + +Used if chdir has no argument and HOME is not set. + +=item PATH + +Used in executing subprocesses, and in finding the program if B<-S> is +used. + +=item PERL5LIB + +A colon-separated list of directories in which to look for Perl library +files before looking in the standard library and the current +directory. 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 B<-T> switch was used), neither variable is used. +The program should instead say: + + use lib "/my/directory"; + +=item PERL5OPT + +Command-line options (switches). Switches in this variable are taken +as if they were on every Perl command line. Only the B<-[DIMUdmw]> +switches are allowed. When running taint checks (because the program +was running setuid or setgid, or the B<-T> switch was used), this +variable is ignored. If PERL5OPT begins with B<-T>, tainting will be +enabled, and any subsequent options ignored. +=item 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. + +=item PERL5DB + +The command used to load the debugger code. The default is: + + BEGIN { require 'perl5db.pl' } + +=item PERL5SHELL (specific to the Win32 port) + +May be set to an alternative shell that perl must use internally for +executing "backtick" commands or system(). Default is C +on WindowsNT and C on Windows95. The value is considered +to be space-separated. Precede any character that needs to be protected +(like a space or backslash) with a backslash. + +Note that Perl doesn't use COMSPEC for this purpose because +COMSPEC has a high degree of variability among users, leading to +portability concerns. Besides, perl can use a shell that may not be +fit for interactive use, and setting COMSPEC to such a shell may +interfere with the proper functioning of other programs (which usually +look in COMSPEC to find a shell fit for interactive use). + +=item PERL_DEBUG_MSTATS + +Relevant only if perl is compiled with the malloc included with the perl +distribution (that is, if C 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. + +=item PERL_DESTRUCT_LEVEL + +Relevant only if your perl executable was built with B<-DDEBUGGING>, +this controls the behavior of global destruction of objects and other +references. =back + +Perl also has environment variables that control how Perl handles data +specific to particular natural languages. See L. + +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)};