Perl script in bash's HereDoc - perl

Question

Is possible somewhat write a perl script in a bash script as heredoc?
This is not working (example only)
#/bin/bash
perl <<EOF
while(<>) {
chomp;
print "xxx: $_\n";
}
EOF
Is here some nice way how to embed a perl script into a bash script? Want run perl script from an bash script and don't want put it into external file.

Answer 1

The problem here is that the script is being passed to perl on stdin, so trying to process stdin from the script doesn't work.
1. String literal
perl -e '
while(<>) {
chomp;
print "xxx: $_\n";
}
'
Using a string literal is the most direct way to write this, though it's not ideal if the Perl script contains single quotes itself.
2. Use perl -e
#/bin/bash
script=$(cat <<'EOF'
while(<>) {
chomp;
print "xxx: $_\n";
}
EOF
)
perl -e "$script"
If you pass the script to perl using perl -e then you won't have the stdin problem and you can use any characters you like in the script. It's a bit roundabout to do this, though. Heredocs yield input on stdin and we need strings. What to do? Oh, I know! This calls for $(cat <<HEREDOC).
Make sure to use <<'EOF' rather than just <<EOF to keep bash from doing variable interpolation inside the heredoc.
You could also write this without the $script variable, although it's getting awfully hairy now!
perl -e "$(cat <<'EOF'
while(<>) {
chomp;
print "xxx: $_\n";
}
EOF
)"
3. Process substitution
perl <(cat <<'EOF'
while(<>) {
chomp;
print "xxx: $_\n";
}
EOF
)
Along the lines of #2, you can use a bash feature called process substitution which lets you write <(cmd) in place of a file name. If you use this you don't need the -e since you're now passing perl a file name rather than a string.

Answer 2

You know I never thought of this.
The answer is "YES!" it does work. As others have mentioned, <STDIN> can't be used, but this worked fine:
$ perl <<'EOF'
print "This is a test\n";
for $i ( (1..3) ) {
print "The count is $i\n";
}
print "End of my program\n";
EOF
This is a test
The count is 1
The count is 2
The count is 3
End of my program
In Kornshell and in BASH, if you surround your end of here document string with single quotes, the here document isn't interpolated by the shell.

Answer 3

Only small corection of #John Kugelman's answer. You can eliminate the useless cat and use:
read -r -d '' perlscript <<'EOF'
while(<>) {
chomp;
print "xxx: $_\n";
}
EOF
perl -e "$perlscript"

Answer 4

Here's another way to use a PERL HEREDOC script within bash, and take full advantage it.
#!/bin/sh
#If you are not passing bash var's and single quote the HEREDOC tag
perl -le "$(cat <<'MYPL'
# Best to build your out vars rather than writing directly
# to the pipe until the end.
my $STDERRdata="", $STDOUTdata="";
while ($i=<STDIN>){ chomp $i;
$STDOUTdata .= "To stdout\n";
$STDERRdata .= "Write from within the heredoc\n";
MYPL
print $STDOUTdata; #Doing the pipe write at the end
warn $STDERRdata; #will save you a lot of frustration.
)" [optional args] <myInputFile 1>prints.txt 2>warns.txt
or
#!/bin/sh
set WRITEWHAT="bash vars"
#If you want to include your bash var's
#Escape the $'s that are not bash vars, and double quote the HEREDOC tag
perl -le "$(cat <<"MYPL"
my $STDERRdata="", $STDOUTdata="";
while (\$i=<STDIN>){ chomp \$i;
\$STDOUTdata .= "To stdout\n";
\$STDERRdata .= "Write $WRITEWHAT from within the heredoc\n";
MYPL
print \$STDOUTdata; #Doing the pipe write at the end
warn \$STDERRdata; #will save you a lot of frustration.
)" [optional args] <myInputFile 1>prints.txt 2>warns.txt