B::Showlex

Section: Perl Programmers Reference Guide (3pm)
Updated: 2021-03-31
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NAME

B::Showlex - Show lexical variables used in functions or files  

SYNOPSIS

        perl -MO=Showlex[,-OPTIONS][,SUBROUTINE] foo.pl
 

DESCRIPTION

When a comma-separated list of subroutine names is given as options, Showlex prints the lexical variables used in those subroutines. Otherwise, it prints the file-scope lexicals in the file.  

EXAMPLES

Traditional form: 

 $ perl -MO=Showlex -e 'my ($i,$j,$k)=(1,"foo")'
 Pad of lexical names for comppadlist has 4 entries
 0: (0x8caea4) undef
 1: (0x9db0fb0) $i
 2: (0x9db0f38) $j
 3: (0x9db0f50) $k
 Pad of lexical values for comppadlist has 5 entries
 0: SPECIAL #1 &PL_sv_undef
 1: NULL (0x9da4234)
 2: NULL (0x9db0f2c)
 3: NULL (0x9db0f44)
 4: NULL (0x9da4264)
 -e syntax OK

New-style form: 

 $ perl -MO=Showlex,-newlex -e 'my ($i,$j,$k)=(1,"foo")'
 main Pad has 4 entries
 0: (0x8caea4) undef
 1: (0xa0c4fb8) "$i" = NULL (0xa0b8234)
 2: (0xa0c4f40) "$j" = NULL (0xa0c4f34)
 3: (0xa0c4f58) "$k" = NULL (0xa0c4f4c)
 -e syntax OK

New form, no specials, outside O framework: 

 $ perl -MB::Showlex -e \
    'my ($i,$j,$k)=(1,"foo"); B::Showlex::compile(-newlex,-nosp)->()'
 main Pad has 4 entries
 1: (0x998ffb0) "$i" = IV (0x9983234) 1
 2: (0x998ff68) "$j" = PV (0x998ff5c) "foo"
 3: (0x998ff80) "$k" = NULL (0x998ff74)

Note that this example shows the values of the lexicals, whereas the other examples did not (as they're compile-time only).  

OPTIONS

The "-newlex" option produces a more readable "name => value" format, and is shown in the second example above.

The "-nosp" option eliminates reporting of SPECIALs, such as "0: SPECIAL #1 &PL_sv_undef" above. Reporting of SPECIALs can sometimes overwhelm your declared lexicals.  

SEE ALSO

B::Showlex can also be used outside of the O framework, as in the third example. See B::Concise for a fuller explanation of reasons.  

TODO

Some of the reported info, such as hex addresses, is not particularly valuable. Other information would be more useful for the typical programmer, such as line-numbers, pad-slot reuses, etc.. Given this, -newlex is not a particularly good flag-name.  

AUTHOR

Malcolm Beattie, "mbeattie@sable.ox.ac.uk"

 

Index

NAME
SYNOPSIS
DESCRIPTION
EXAMPLES
OPTIONS
SEE ALSO
TODO
AUTHOR