Re: running programs from PERL

Beyond Alexander's tips, there's one more thing that bugs me:

You chdir to $current_dir, then prepend $current_dir/ to your command. Works nicely on Unix for $current_dir being absolute or . or ./. . But for "" or a non-trivial relative path, you're in for a surprise... .

One way to cope is prepending $ENV{PWD}/ to a relative path. Note that $ENV{PWD} isn't updated by chdir(), being set by the shell. Note 2: Better yet, check Anonymous' File::chdir pointer below and prepend $CWD instead (thx, this elimininates most of the chdir pains! Note2Self: my($CWD) stops the chdir side effect of assigning. Good.).

Ad afoken's warning on using the shell:

If you restrict yourself to Unix (and CYGWIN), you normally can assume at least a Bourne-style or POSIX shell, which allows a nice idiom using %ENV to avoid severe secure quoting headaches: $ENV{f}="...";system qq{ls -l -- "\$f"};.

Open Question: Windows processes should support %ENV as part of their POSIX support. What is be the corresponding secure Windows-NON-CYGWIN-idiom for the Unix shell's variable interpolation w/o word splitting, i.e. "$f"?

cu & HTH, Peter -- hints may be untested unless stated otherwise; use with caution & understanding.

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Re^2: running programs from PERL by cdarke (Prior) on Oct 25, 2009 at 13:01 UTC
Open Question: Windows processes should support %ENV as part of their POSIX support. What is be the corresponding secure Windows-NON-CYGWIN-idiom for the Unix shell's variable interpolation w/o word splitting, i.e. "$f"? Windows processes do have an environment block, but it is nothing to do with POSIX support. Do not confuse the operating system with the shell - Korn shell 93, for example (via uwin) runs on Windows. It is not that difficult to write a shell which runs on UNIX and Windows (I have done it, so it can't be hard). The Microsoft cmd.exe shell only uses double-quotes (as does awk) but does not use the $ operator to get a variable value, as is common in some shells, but it uses the % delimiter, as in %PATH%. Coming from a UNIX background I think it is safe to say that cmd.exe does not support interpolation as we know it. By the way, environment variables in Windows are not case-sensitive, so %PATH% is the same as %path% (unlike the c-shell). For example: `C:\>set fred=42 C:\>perl -e "print \"$ENV{FRED}\n\"" 42` [download] Cygwin (and uwin) makes Windows environment variables UPPERCASE, and is case-sensitive.	[reply] [d/l]
Windows viewpoint?-- Re^3: running programs from PERL by jakobi (Pilgrim) on Oct 25, 2009 at 14:43 UTC
~~With POSIX support I meant the libc and lower portions of POSIX and I was under the impression that e.g~~ POSIX exec() ~~was part of whatever was once enough to give Microsoft some claim of POSIX compatibility certifications for NT and later.~~ Looks like I badly misremembered things. My original question is the reverse of your example: Can I e.g. set $ENV{VARIABLE} in a non-CYGWIN-port of Perl, and then use system q{dir "%VARIABLE%"} to have cmd.exe expand the variable? More specifically, what happens if the variable contains `[\n \\;"']`? A new question/request: What I'd love to do is appending a link to a node giving the comparable portable (or windows) version of `$ENV{f}="a b; 'c'"; system q{dir "\$f"}`. Alternately at most a single concise paragraph as a footnote on the windows side of things to Re: SAFE use of string in system command. Otherwise its a bit unfair if the Unix view hogs all the good keywords and doesn't help a windows SoPW :) What I currently have - after some searching on PerlMonks - is a mess and a headache (and a bit of glee in lacking the windows environment to test this mess). It reads like system/exec/(pipe-)open should be avoided on Windows for non-trivial commands, preferring IPC::System::Simple or Win32::Process::Create instead. asychronnous system(1,...) magic to replace start (windows) or a final '&' (unix). lack of fork(): What is the difference between Windows fork an Unix fork ?, with a mismatched substitute in Win32::Process (archived copy of Mr. Peabody Explains fork()) Construct command portable way Perl Background processes in Windows How to Start a Process in a Remote Win32 Machine using Perl and WMI help needede in backticks(``) and system function Non-shell-invoking system/exec and qx// Windows command line; incl. cmd.exe quoting surprises Do we have a better explanation or tutorial already on PerlMonks or do you know of a suitable resource outside? Merci! cu & thanx, Peter -- hints may be untested unless stated otherwise; use with caution & understanding.	[reply] [d/l] [select]
Re^2: running programs from PERL by Anonymous Monk on Oct 25, 2009 at 10:34 UTC
$ENV{PWD} is not portable `use File::chdir; $CWD = "/foo/bar"; # now in /foo/bar { local $CWD = "/moo/baz"; # now in /moo/baz ... } # still in /foo/bar!` [download]	[reply] [d/l]


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