Perl 5 version 10.1 documentation



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


  1. 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:

  1. $ perl -MO=Showlex -e 'my ($i,$j,$k)=(1,"foo")'
  2. Pad of lexical names for comppadlist has 4 entries
  3. 0: SPECIAL #1 &PL_sv_undef
  4. 1: PVNV (0x9db0fb0) $i
  5. 2: PVNV (0x9db0f38) $j
  6. 3: PVNV (0x9db0f50) $k
  7. Pad of lexical values for comppadlist has 5 entries
  8. 0: SPECIAL #1 &PL_sv_undef
  9. 1: NULL (0x9da4234)
  10. 2: NULL (0x9db0f2c)
  11. 3: NULL (0x9db0f44)
  12. 4: NULL (0x9da4264)
  13. -e syntax OK

New-style form:

  1. $ perl -MO=Showlex,-newlex -e 'my ($i,$j,$k)=(1,"foo")'
  2. main Pad has 4 entries
  3. 0: SPECIAL #1 &PL_sv_undef
  4. 1: PVNV (0xa0c4fb8) "$i" = NULL (0xa0b8234)
  5. 2: PVNV (0xa0c4f40) "$j" = NULL (0xa0c4f34)
  6. 3: PVNV (0xa0c4f58) "$k" = NULL (0xa0c4f4c)
  7. -e syntax OK

New form, no specials, outside O framework:

  1. $ perl -MB::Showlex -e \
  2. 'my ($i,$j,$k)=(1,"foo"); B::Showlex::compile(-newlex,-nosp)->()'
  3. main Pad has 4 entries
  4. 1: PVNV (0x998ffb0) "$i" = IV (0x9983234) 1
  5. 2: PVNV (0x998ff68) "$j" = PV (0x998ff5c) "foo"
  6. 3: PVNV (0x998ff80) "$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 isnt a particularly good flag-name.


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


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