+The cases when the shell is used are:
+
+=over
+
+=item 1
+
+One-argument system() (see L<perlfunc/system>), exec() (see L<perlfunc/exec>)
+with redirection or shell meta-characters;
+
+=item 2
+
+Pipe-open (see L<perlfunc/open>) with the command which contains redirection
+or shell meta-characters;
+
+=item 3
+
+Backticks C<``> (see L<perlop/"I/O Operators">) with the command which contains
+redirection or shell meta-characters;
+
+=item 4
+
+If the executable called by system()/exec()/pipe-open()/C<``> is a script
+with the "magic" C<#!> line or C<extproc> line which specifies shell;
+
+=item 5
+
+If the executable called by system()/exec()/pipe-open()/C<``> is a script
+without "magic" line, and C<$ENV{EXECSHELL}> is set to shell;
+
+=item 6
+
+If the executable called by system()/exec()/pipe-open()/C<``> is not
+found;
+
+=item 7
+
+For globbing (see L<perlfunc/glob>, L<perlop/"I/O Operators">).
+
+=back
+
+For the sake of speed for a common case, in the above algorithms
+backslashes in the command name are not considered as shell metacharacters.
+
+Perl starts scripts which begin with cookies
+C<extproc> or C<#!> directly, without an intervention of shell. Perl uses the
+same algorithm to find the executable as F<pdksh>: if the path
+on C<#!> line does not work, and contains C</>, then the executable
+is searched in F<.> and on C<PATH>. To find arguments for these scripts
+Perl uses a different algorithm than F<pdksh>: up to 3 arguments are
+recognized, and trailing whitespace is stripped.
+
+If a script
+does not contain such a cooky, then to avoid calling F<sh.exe>, Perl uses
+the same algorithm as F<pdksh>: if C<$ENV{EXECSHELL}> is set, the
+script is given as the first argument to this command, if not set, then
+C<$ENV{COMSPEC} /c> is used (or a hardwired guess if C<$ENV{COMSPEC}> is
+not set).
+
+If starting scripts directly, Perl will use exactly the same algorithm as for
+the search of script given by B<-S> command-line option: it will look in
+the current directory, then on components of C<$ENV{PATH}> using the
+following order of appended extensions: no extension, F<.cmd>, F<.btm>,
+F<.bat>, F<.pl>.
+
+Note that Perl will start to look for scripts only if OS/2 cannot start the
+specified application, thus C<system 'blah'> will not look for a script if
+there is an executable file F<blah.exe> I<anywhere> on C<PATH>.
+
+Note also that executable files on OS/2 can have an arbitrary extension,
+but F<.exe> will be automatically appended if no dot is present in the name.
+The workaround as as simple as that: since F<blah.> and F<blah> denote the
+same file, to start an executable residing in file F<n:/bin/blah> (no
+extension) give an argument C<n:/bin/blah.> to system().
+
+The last note is that currently it is not straightforward to start PM
+programs from VIO (=text-mode) Perl process and visa versa. Either ensure
+that shell will be used, as in C<system 'cmd /c epm'>, or start it using
+optional arguments to system() documented in C<OS2::Process> module. This
+is considered a bug and should be fixed soon.
+
https://perl5.git.perl.org / perl5.git / blobdiff