Daftar Isi

• NAME
• SYNOPSIS
• DESCRIPTION
  • OPTIONS
  • "Considerations"
• ENVIRONMENT
• AUTHOR
• FILES
• SEE ALSO
• DIAGNOSTICS
• BUGS

NAME

a2p - Awk to Perl translator

SYNOPSIS

a2p [options] [filename]

DESCRIPTION

A2p takes an awk script specified on the command line (or fromstandard input) and produces a comparable perl script on thestandard output.

OPTIONS

Options include:

• -D<number>

  sets debugging flags.

• -F<character>

  tells a2p that this awk script is always invoked with this -Fswitch.

• -n<fieldlist>

  specifies the names of the input fields if input does not have to besplit into an array. If you were translating an awk script thatprocesses the password file, you might say:

  a2p -7 -nlogin.password.uid.gid.gcos.shell.home
   

  Any delimiter can be used to separate the field names.

• -<number>

  causes a2p to assume that input will always have that many fields.

• -o

  tells a2p to use old awk behavior. The only current differences are:

  • Old awk always has a line loop, even if there are no lineactions, whereas new awk does not.

  • In old awk, sprintf is extremely greedy about its arguments.For example, given the statement

    print sprintf(some_args), extra_args;
     

    old awk considers extra_args to be arguments to sprintf; new awkconsiders them arguments to print.

"Considerations"

A2p cannot do as good a job translating as a human would, but itusually does pretty well. There are some areas where you may want toexamine the perl script produced and tweak it some. Here are some ofthem, in no particular order.

There is an awk idiom of putting int() around a string expression toforce numeric interpretation, even though the argument is alwaysinteger anyway. This is generally unneeded in perl, but a2p can'ttell if the argument is always going to be integer, so it leaves itin. You may wish to remove it.

Perl differentiates numeric comparison from string comparison. Awkhas one operator for both that decides at run time which comparison todo. A2p does not try to do a complete job of awk emulation at thispoint. Instead it guesses which one you want. It's almost alwaysright, but it can be spoofed. All such guesses are marked with thecomment "#???". You should go through and check them. You mightwant to run at least once with the -w switch to perl, which willwarn you if you use == where you should have used eq.

Perl does not attempt to emulate the behavior of awk in whichnonexistent array elements spring into existence simply by beingreferenced. If somehow you are relying on this mechanism to createnull entries for a subsequent for...in, they won't be there in perl.

If a2p makes a split line that assigns to a list of variables thatlooks like (Fld1, Fld2, Fld3...) you may want to rerun a2p using the-n option mentioned above. This will let you name the fieldsthroughout the script. If it splits to an array instead, the scriptis probably referring to the number of fields somewhere.

The exit statement in awk doesn't necessarily exit; it goes to the ENDblock if there is one. Awk scripts that do contortions within the ENDblock to bypass the block under such circumstances can be simplifiedby removing the conditional in the END block and just exiting directlyfrom the perl script.

Perl has two kinds of array, numerically-indexed and associative.Perl associative arrays are called "hashes". Awk arrays are usuallytranslated to hashes, but if you happen to know that the index isalways going to be numeric you could change the {...} to [...].Iteration over a hash is done using the keys() function, but iterationover an array is NOT. You might need to modify any loop that iteratesover such an array.

Awk starts by assuming OFMT has the value %.6g. Perl starts byassuming its equivalent, $#, to have the value %.20g. You'll want toset $# explicitly if you use the default value of OFMT.

Near the top of the line loop will be the split operation that isimplicit in the awk script. There are times when you can move thisdown past some conditionals that test the entire record so that thesplit is not done as often.

For aesthetic reasons you may wish to change index variables from being1-based (awk style) to 0-based (Perl style). Be sure to change alloperations the variable is involved in to match.

Cute comments that say "# Here is a workaround because awk is dumb"are passed through unmodified.

Awk scripts are often embedded in a shell script that pipes stuff intoand out of awk. Often the shell script wrapper can be incorporatedinto the perl script, since perl can start up pipes into and out ofitself, and can do other things that awk can't do by itself.

Scripts that refer to the special variables RSTART and RLENGTH canoften be simplified by referring to the variables $`, $& and $', aslong as they are within the scope of the pattern match that sets them.

The produced perl script may have subroutines defined to deal withawk's semantics regarding getline and print. Since a2p usually pickscorrectness over efficiency. it is almost always possible to rewritesuch code to be more efficient by discarding the semantic sugar.

For efficiency, you may wish to remove the keyword from any returnstatement that is the last statement executed in a subroutine. A2pcatches the most common case, but doesn't analyze embedded blocks forsubtler cases.

ARGV[0] translates to $ARGV0, but ARGV[n] translates to $ARGV[$n-1]. Aloop that tries to iterate over ARGV[0] won't find it.

ENVIRONMENT

A2p uses no environment variables.

AUTHOR

Larry Wall <[email protected]>

FILES

SEE ALSO

 perlThe perl compiler/interpreter
 
 
 
 s2psed to perl translator
 

DIAGNOSTICS

BUGS

It would be possible to emulate awk's behavior in selecting stringversus numeric operations at run time by inspection of the operands,but it would be gross and inefficient. Besides, a2p almost alwaysguesses right.

Storage for the awk syntax tree is currently static, and can run out.