IRIX Base Documentation 1998 November

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PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) NNNNAAAAMMMMEEEE perlrun - how to execute the Perl interpreter SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS ppppeeeerrrrllll [ ----ssssTTTTuuuuUUUU ] [ ----hhhhvvvv ] [ ----VVVV[:_c_o_n_f_i_g_v_a_r] ] [ ----ccccwwww ] [ ----dddd[:_d_e_b_u_g_g_e_r] ] [ ----DDDD[_n_u_m_b_e_r/_l_i_s_t] ] [ ----ppppnnnnaaaa ] [ ----FFFF_p_a_t_t_e_r_n ] [ ----llll[_o_c_t_a_l] ] [ ----0000[_o_c_t_a_l] ] [ ----IIII_d_i_r ] [ ----mmmm[----]_m_o_d_u_l_e ] [ ----MMMM[----]'_m_o_d_u_l_e...' ] [ ----PPPP ] [ ----SSSS ] [ ----xxxx[_d_i_r] ] [ ----iiii[_e_x_t_e_n_s_i_o_n] ] [ ----eeee '_c_o_m_m_a_n_d' ] [ -------- ] [ _p_r_o_g_r_a_m_f_i_l_e ] [ _a_r_g_u_m_e_n_t ]... DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN Upon startup, Perl looks for your script in one of the following places: 1. Specified line by line via ----eeee 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.) 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. With methods 2 and 3, Perl starts parsing the input file from the beginning, unless you've specified a ----xxxx 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 embedded in a larger message. (In this case you would indicate the end of the script 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 ----xxxx 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 ----IIII switch could also cause odd results. Some switches do care if they are processed twice, for instance combinations of ----llll and ----0000. Either put all the switches after the 32 character boundary (if applicable), or replace the use of ----0000_d_i_g_i_t_s by BEGIN{ $/ = "\0digits"; }. PPPPaaaaggggeeee 1111 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) 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 ${1+"$@"}' if $running_under_some_shell; to let Perl see the ----pppp switch. 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 script, Perl compiles the entire script 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 part-way through before finding a syntax error.) If the script is syntactically correct, it is executed. If the script runs off the end without hitting an _e_x_i_t() or _d_i_e() operator, an implicit exit(0) is provided to indicate successful completion. ####!!!! aaaannnndddd qqqquuuuoooottttiiiinnnngggg oooonnnn nnnnoooonnnn----UUUUnnnniiiixxxx ssssyyyysssstttteeeemmmmssss 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 script, and codify it in ALTERNATIVE_SHEBANG (see the _d_o_s_i_s_h._h file in the source distribution for more information). Win95/NT The Win95/NT installation, when using the Activeware port of Perl, will modify the Registry to associate the .pl extension with the perl interpreter. If you install another port of Perl, including the one in the Win32 directory of the Perl distribution, then you'll have to modify the Registry yourself. Macintosh Macintosh perl scripts will have the appropriate Creator and Type, so that double-clicking them will invoke the perl application. PPPPaaaaggggeeee 2222 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) 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 _N_O_T 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 was 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. SSSSwwwwiiiittttcccchhhheeeessss A single-character switch may be combined with the following switch, if any. #!/usr/bin/perl -spi.bak # same as -s -p -i.bak Switches include: PPPPaaaaggggeeee 3333 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) ----0000[_d_i_g_i_t_s] 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 ffffiiiinnnndddd which can print filenames terminated by the null character, you can say this: find . -name '*.bak' -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. ----aaaa turns on autosplit mode when used with a ----nnnn or ----pppp. An implicit split command to the @F array is done as the first thing inside the implicit while loop produced by the ----nnnn or ----pppp. perl -ane 'print pop(@F), "\n";' is equivalent to while (<>) { @F = split(' '); print pop(@F), "\n"; } An alternate delimiter may be specified using ----FFFF. ----cccc causes Perl to check the syntax of the script and then exit without executing it. Actually, it _w_i_l_l execute BEGIN, END, and use blocks, because these are considered as occurring outside the execution of your program. ----dddd runs the script under the Perl debugger. See the _p_e_r_l_d_e_b_u_g manpage. ----dddd::::_f_o_o runs the script under the control of a debugging or tracing module installed as Devel::foo. E.g., ----dddd::::DDDDPPPPrrrrooooffff executes the script using the Devel::DProf profiler. See the _p_e_r_l_d_e_b_u_g manpage. ----DDDD_l_e_t_t_e_r_s ----DDDD_n_u_m_b_e_r sets debugging flags. To watch how it executes your script, use ----DDDDttttllllssss. (This works only if debugging is compiled into your Perl.) Another nice value is ----DDDDxxxx, which lists your compiled syntax tree. And ----DDDDrrrr displays compiled regular expressions. As an alternative, specify a number instead of list of letters (e.g., ----DDDD11114444 is equivalent to ----DDDDttttllllssss): PPPPaaaaggggeeee 4444 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) 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 (not supported anymore) 8192 H Hash dump -- usurps values() 16384 X Scratchpad allocation 32768 D Cleaning up ----eeee _c_o_m_m_a_n_d_l_i_n_e may be used to enter one line of script. If ----eeee is given, Perl will not look for a script filename in the argument list. Multiple ----eeee commands may be given to build up a multi-line script. Make sure to use semicolons where you would in a normal program. ----FFFF_p_a_t_t_e_r_n specifies the pattern to split on if ----aaaa is also in effect. The pattern may be surrounded by //, "", or '', otherwise it will be put in single quotes. ----hhhh prints a summary of the options. ----iiii[_e_x_t_e_n_s_i_o_n] 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 _p_r_i_n_t() 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 $ perl -p -i.bak -e "s/foo/bar/; ... " is the same as using the script: #!/usr/bin/perl -pi.bak s/foo/bar/; which is equivalent to PPPPaaaaggggeeee 5555 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) #!/usr/bin/perl while (<>) { if ($ARGV ne $oldargv) { rename($ARGV, $ARGV . '.bak'); open(ARGVOUT, ">$ARGV"); select(ARGVOUT); $oldargv = $ARGV; } s/foo/bar/; } continue { print; # this prints to original filename } select(STDOUT); except that the ----iiii form doesn't need to compare $ARGV to $oldargv to know when the filename has changed. It does, however, use ARGVOUT for the selected filehandle. Note that STDOUT is restored as the default output filehandle after the loop. You can use eof without parenthesis to locate the end of each input file, in case you want to append to each file, or reset line numbering (see example in the eof entry in the _p_e_r_l_f_u_n_c manpage). ----IIII_d_i_r_e_c_t_o_r_y Directories specified by ----IIII are prepended to the search path for modules (@INC), and also tells the C preprocessor where to search for include files. The C preprocessor is invoked with ----PPPP; by default it searches /usr/include and /usr/lib/perl. ----llll[_o_c_t_n_u_m] enables automatic line-ending processing. It has two effects: first, it automatically chomps "$/" (the input record separator) when used with ----nnnn or ----pppp, and second, it assigns "$\" (the output record separator) to have the value of _o_c_t_n_u_m so that any print statements will have that separator added back on. If _o_c_t_n_u_m is omitted, sets "$\" 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 ----llll switch is followed by a ----0000 switch: gnufind / -print0 | perl -ln0e 'print "found $_" if -p' This sets $\ to newline and then sets $/ to the null character. ----mmmm[----]_m_o_d_u_l_e PPPPaaaaggggeeee 6666 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) ----MMMM[----]_m_o_d_u_l_e ----MMMM[----]'_m_o_d_u_l_e ...' ----[[[[mmmmMMMM]]]][----]_m_o_d_u_l_e=_a_r_g[,_a_r_g]... -m_m_o_d_u_l_e executes use _m_o_d_u_l_e (); before executing your script. -M_m_o_d_u_l_e executes use _m_o_d_u_l_e ; before executing your script. You can use quotes to add extra code after the module name, e.g., -M'module 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 -M'module 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. ----nnnn causes Perl to assume the following loop around your script, which makes it iterate over filename arguments somewhat like sssseeeedddd ----nnnn or aaaawwwwkkkk: while (<>) { ... # your script goes here } Note that the lines are not printed by default. See ----pppp 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 ffffiiiinnnndddd because you don't have to start a process on every filename found. BEGIN and END blocks may be used to capture control before or after the implicit loop, just as in aaaawwwwkkkk. ----pppp causes Perl to assume the following loop around your script, which makes it iterate over filename arguments somewhat like sssseeeedddd: while (<>) { ... # your script goes here } continue { print or die "-p destination: $!\n"; } PPPPaaaaggggeeee 7777 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) If a file named by an argument cannot be opened for some reason, Perl warns you about it, and moves on to the next file. Note that the lines are printed automatically. An error occuring during printing is treated as fatal. To suppress printing use the ----nnnn switch. A ----pppp overrides a ----nnnn switch. BEGIN and END blocks may be used to capture control before or after the implicit loop, just as in awk. ----PPPP causes your script to be run through the C preprocessor before compilation by Perl. (Because both comments and cpp directives begin with the # character, you should avoid starting comments with any words recognized by the C preprocessor such as "if", "else", or "define".) ----ssss enables some rudimentary switch parsing for switches on the command line after the script name but before any filename arguments (or before a --------). Any switch found there is removed from @ARGV and sets the corresponding variable in the Perl script. The following script prints "true" if and only if the script is invoked with a ----xxxxyyyyzzzz switch. #!/usr/bin/perl -s if ($xyz) { print "true\n"; } ----SSSS makes Perl use the PATH environment variable to search for the script (unless the name of the script 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. If the file supplied contains directory separators (i.e. it is an absolute or relative pathname), and if the 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 script 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 script will be searched for strictly on the PATH. 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: PPPPaaaaggggeeee 8888 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) #!/usr/bin/perl eval 'exec /usr/bin/perl -S $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 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 ----SSSS tells Perl to search for the script if necessary. After Perl locates the script, it parses the lines and ignores them because the variable $running_under_some_shell is never true. A better construct than $* would be ${1+"$@"}, 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 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 /usr/bin/perl -S $0 ${1+"$@"}' & eval 'exec /usr/bin/perl -S $0 $argv:q' if $running_under_some_shell; ----TTTT 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 the _p_e_r_l_s_e_c manpage. ----uuuu 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 uuuunnnndddduuuummmmpppp 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 _d_u_m_p() operator instead. Note: availability of uuuunnnndddduuuummmmpppp is platform specific and may not be available for a specific port of Perl. ----UUUU 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 ----wwww switch (or the $^W variable) must be used along with this option to actually ggggeeeennnneeeerrrraaaatttteeee the taint- check warnings. ----vvvv prints the version and patchlevel of your Perl executable. ----VVVV prints summary of the major perl configuration values and the current value of @INC. PPPPaaaaggggeeee 9999 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) ----VVVV::::_n_a_m_e Prints to STDOUT the value of the named configuration variable. ----wwww 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. You can disable specific warnings using __WARN__ hooks, as described in the _p_e_r_l_v_a_r manpage and the warn entry in the _p_e_r_l_f_u_n_c manpage. See also the _p_e_r_l_d_i_a_g manpage and the _p_e_r_l_t_r_a_p manpage. ----xxxx _d_i_r_e_c_t_o_r_y 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 ----xxxx switch controls only the disposal of leading garbage. The script must be terminated with __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). EEEENNNNVVVVIIIIRRRROOOONNNNMMMMEEEENNNNTTTT 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 script if ----SSSS 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. If PERL5LIB is not defined, PERLLIB is used. When running taint checks (because the script was running setuid or setgid, or the ----TTTT switch was used), neither variable is used. The script 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 ----[[[[DDDDIIIIMMMMUUUUddddmmmmwwww]]]] switches are allowed. When running taint checks (because the script was running setuid or setgid, or the ----TTTT switch was used), this variable is ignored. PPPPaaaaggggeeee 11110000 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) 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 WIN32 port) May be set to an alternative shell that perl must use internally for executing "backtick" commands or _s_y_s_t_e_m(). 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 your perl executable was built with ----DDDDDDDDEEEEBBBBUUUUGGGGGGGGIIIINNNNGGGG____MMMMSSSSTTTTAAAATTTTSSSS, 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 ----DDDDDDDDEEEEBBBBUUUUGGGGGGGGIIIINNNNGGGG, this controls the behavior of global destruction of objects and other references. Perl also has environment variables that control how Perl handles data specific to particular natural languages. See the _p_e_r_l_l_o_c_a_l_e manpage. Apart from these, Perl uses no other environment variables, except to make them available to the script being executed, and to child processes. However, scripts running setuid would do well to execute 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)}; PPPPaaaaggggeeee 11111111 PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPEEEERRRRLLLLRRRRUUUUNNNN((((1111)))) PPPPaaaaggggeeee 11112222