Foreword During lasts weeks seems I was very active in producing oneliners (so much that I'm tempted to write some tutorial about some useful teqniques).

In one oneliner where i was fixed for a parametrizable solution i come across the -s perl's switch, that i admit I was completely unaware of.

In perlrun few lines are dedicated to it. It is somtehing difficult to search informantions for, but I found:

• it is mentioned in Parsing your script's command line
• in -s is evil? where is shown it can override readonly vars like $1
• and in this old and short thread

From what i understand from official docs it works on the shebang line: it must also run from command line for oneliners and other programs too.

Let's see what I tested given simple.pl program as follow:

    # use strict;     # UPDATE: that was commented as spotted by Eily 
+( see below)
    # use warnings;   # UPDATE

    BEGIN{print "inside BEGIN  \@ARGV is [@ARGV]\n"}

    my $test='original value';

    print       "inside main   \@ARGV is [@ARGV] and \$test is [$test]
+\n";
[download]

    perl -s simple.pl -test=SET_VIA_-s arg1
    inside BEGIN  @ARGV is [arg1] and $test is [SET_VIA_-s]
    inside main   @ARGV is [arg1] and $test is [original value]
[download]

Ie $test is set by the commandline switch -test=SET_VIA_-s and is visible in the BEGIN then the body of the program gives it another value original value Why this does not deparse to anything visible (as opposite of other switches like -l -n -p -a -F )?

    perl -MO=Deparse -s simple.pl -test=SET_VIA_-s arg1
    inside BEGIN  @ARGV is [arg1] and $test is [SET_VIA_-s]
    sub BEGIN {
    print "inside BEGIN  \@ARGV is [@ARGV] and \$test is [$test]\n";
    }
    my $test = 'original value';
    print "inside main   \@ARGV is [@ARGV] and \$test is [$test]\n";
    simple.pl syntax OK
[download]

while in the oneliner version (without strict and warnings)

    perl -se "BEGIN{print qq(inside BEGIN  \@ARGV is [@ARGV]\n)};print
+ qq(inside main   \@ARGV is [@ARGV] and \$test is [$test]\n);"  
            -test=SET_VIA_-s arg1

    inside BEGIN  @ARGV is [arg1]
    Can't modify constant item in scalar assignment at -e line 2, near
+ "SET_VIA_-s"
    syntax error at -e line 2, near "SET_VIA_-s"
    Execution of -e aborted due to compilation errors.
[download]

    perl -se "BEGIN{print qq(inside BEGIN  \@ARGV is [@ARGV]\n)};print
+ qq(inside main   \@ARGV is [@ARGV] and \$test is [$test]\n);" 
             -- -test=SET_VIA_-s arg1

    inside BEGIN  @ARGV is [arg1]
    inside main   @ARGV is [arg1] and $test is [SET_VIA_-s]
[download]

But adding strict and warnigs and the my declaration for $test (as in simple.pl ) the oneliners version gives different results:

    perl -se "use strict; use warnings;BEGIN{print qq(inside BEGIN  \@
+ARGV is [@ARGV]\n)}my $test='originalvalue';print qq(inside main   \@
+ARGV is [@ARGV] and \$test is [$test]\n);" 
         -- -test=SET_VIA_-s arg1

    inside BEGIN  @ARGV is [arg1]
    inside main   @ARGV is [arg1] and $test is [original value]
[download]

In addition the evil behaviour explained in the above mentioned thread is still active, and evem more incomprensible if you add a qq(..)

    perl -se "'A'=~/(A)/;print $1      " -- -1=OUCH!
    OUCH!

    perl -se "'A'=~/(A)/;print qq($1\n)" -- -1=OUCH!
    A
[download]

personal conclusions about -s switch

• cannot works with scripts that use strict and warnings because cannot ovveride vars declared with my
• works only with oneliners pushing global vars in the namespace
• still has evil and not coherent behaviours

It is said in perlrun that enables rudimentary switches. It is not too reductive word?. Is not worth to spend some word more in the official docs, explaining that MUST be used only in oneliners to act as rudimentary switch's processor (only oneliners examples, not short script)? Are my conclusions correct? Cannot be that switch a candidate to be removed? Why it's usage does not deparse to something visible? what the hell in the last example?

L*