使用来自 bash 的 stdin 的多行 perl 的 heredoc 语法

Question

How to pass file to perl script for processing and also use heredoc syntax for multi-line perl script? I have tried those but no luck:

cat ng.input | perl -nae <<EOF
if (@F==2) {print $F[0] . "\t". $F[1] . "\n"} else { print "\t" . $F[0] . "\n" }
EOF

cat ng.input | perl -nae - <<EOF
if (@F==2) {print $F[0] . "\t". $F[1] . "\n"} else { print "\t" . $F[0] . "\n" }
EOF

Answer 1

There's really no need for here-docs. You could simply use a multi-line argument:

perl -nae'
    if (@F==2) {
       print $F[0] . "\t". $F[1] . "\n"
    } else {
       print "\t" . $F[0] . "\n"
    }
' ng.input

Clean, more portable than Barmar's, and only uses one process instead of Barmar's three.

---

Note that your code could be shrunk to

perl -lane'unshift @F, "" if @F!=2; print "$F[0]\t$F[1]";' ng.input

or even

perl -pale'unshift @F, "" if @F!=2; $_="$F[0]\t$F[1]";' ng.input

Answer 2

Use process substitution:

cat ng.input | perl -na <(cat <<'EOF'
if (@F==2) {print $F[0] . "\t". $F[1] . "\n"} else { print "\t" . $F[0] . "\n" }
EOF
)

Also put single quotes around the EOF tag so that $F in the perl script won't be expanded as shell variables.

Answer 3

Can also pass a heredoc as a "-" first argument to perl:

perl -lna - ng.input <<'EOF'
if (@F==2) {print $F[0] . "\t". $F[1] . "\n"} else { print "\t" . $F[0] . "\n" }
EOF