perl 中字段分隔符的变量

Question

In awk I can write: awk -F: 'BEGIN {OFS = FS} ...'

In Perl, what's the equivalent of FS ? I'd like to write

perl -F: -lane 'BEGIN {$, = [what?]} ...'

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update with an example:

echo a:b:c:d | awk -F: 'BEGIN {OFS = FS} {$2 = 42; print}'
echo a:b:c:d | perl -F: -ane 'BEGIN {$, = ":"} $F[1] = 42; print @F'

Both output a:42:c:d

I would prefer not to hard-code the : in the Perl BEGIN block, but refer to wherever the -F option saves its argument.

Answer 1

To sum up, what I'm looking for does not exist:

1. there's no variable that holds the argument for -F , and more importantly
2. Perl's "FS" is fundamentally a different data type (regular expression) than the "OFS" (string) -- it does not make sense to join a list of strings using a regex.

Note that the same holds true in awk: FS is a string but acts as regex:

echo a:b,c:d | awk -F'[:,]' 'BEGIN {OFS=FS} {$2=42; print}'

outputs " a[:,]42[:,]c[:,]d "

Thanks for the insight and workarounds though.

---

You can use perl's -s (similar to awk's -v ) to pass a "FS" variable, but the split becomes manual:

echo a:b:c:d | perl -sne '
    BEGIN {$, = $FS}
    @F = split $FS;
    $F[1] = 42;
    print @F;
' -- -FS=":"

Answer 2

If you know the exact length of input, you could do this:

echo a:b:c:d | perl -F'(:)' -ane '$, = $F[1]; @F = @F[0,2,4,6]; $F[1] = 42; print @F'

If the input is of variable lengths, you'll need something more sophisticated than @f[0,2,4,6].

-F seems to simply provide input to an automatic split() call, which takes a complete RE as an expression. You may be able to find something more suitable by reading the perldoc entries for split , perlre , and perlvar .

Answer 3

Darnit...

The best I can do is:

echo a:b:c:d | perl -ne '$v=":";@F = split("$v"); $F[1] = 42; print join("$v", @F) . "\n";'

You don't need the -F: this way, and you're only stating the colon once. I was hoping there was someway of setting variables on the command line like you can with Awk's -v switch.

For one liners, Perl is usually not as clean as Awk, but I remember using Awk before I knew of Perl and writing 1000+ line Awk scripts.

Trying things like this made people think Awk was either named after the sound someone made when they tried to decipher such a script, or stood for AWKward.

Answer 4

You can sort of cheat it, because perl is actually using the split function with your -F argument, and you can tell split to preserve what it splits on by including capturing parens in the regex:

$ echo a:b:c:d | perl -F'(:)' -ane 'print join("/", @F);'
a/:/b/:/c/:/d

You can see what perl's doing with some of these "magic" command-line arguments by using -MO=Deparse , like this:

$ perl -MO=Deparse -F'(:)' -ane 'print join("/", @F);'
LINE: while (defined($_ = <ARGV>)) {
    our(@F) = split(/(:)/, $_, 0);
    print join('/', @F);
}
-e syntax OK

You'd have to change your @F subscripts to double what they'd normally be ( $F[2] = 42 ).

Answer 5

There is no input record separator in Perl. You're basically emulating awk by using the -a and -F flags. If you really don't want to hard code the value, then why not just use an environmental variable?

$ export SPLIT=":"
$ perl -F$SPLIT -lane 'BEGIN { $, = $ENV{SPLIT}; } ...'