B::Showlex(3perl) Perl Programmers Reference Guide B::Showlex(3perl)

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

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

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.

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).

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.

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.

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.

Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
2021-05-23 perl v5.34.0