Puppet out:

Debug: Exec[line_remove](provider=posix): Executing '/usr/bin/perl -w -ni -e 'my $qs = quotemeta('ssh-rsa AAAA/BBBB/knMQ== user@host.f.q.d.n'); print unless  /^$qs$/ ' '/root/user/b1.bak''
Debug: Executing: '/usr/bin/perl -w -ni -e 'my $qs = quotemeta('ssh-rsa AAAA/BBBB/knMQ== user@host.f.q.d.n'); print unless  /^$qs$/ ' '/root/user/b1.bak''
Notice: /Stage[main]/Main/Line[ssh_key]/Exec[line_remove]/returns: Unquoted string "ssh" may clash with future reserved word at -e line 1.
Notice: /Stage[main]/Main/Line[ssh_key]/Exec[line_remove]/returns: syntax error at -e line 1, at EOF
Notice: /Stage[main]/Main/Line[ssh_key]/Exec[line_remove]/returns: Execution of -e aborted due to compilation errors.

## Same errors as direct at the cmd line
# /usr/bin/perl -w -ni -e 'my $qs = quotemeta('ssh-rsa AAAA/BBBB/knMQ== user@host.f.q.d.n'); print unless  /^$qs$/ ' '/root/user/b1.bak'
Unquoted string "ssh" may clash with future reserved word at -e line 1.
syntax error at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

# Try swap outer quotes '-> "
# /usr/bin/perl -w -ni -e "my $qs = quotemeta('ssh-rsa AAAA/BBBB/knMQ== user@host.f.q.d.n'); print unless  /^$qs$/ " '/root/user/b1.bak'
syntax error at -e line 1, near "my  ="
Execution of -e aborted due to compilation errors.

# Try "" around quotemeta string
# /usr/bin/perl -w -ni -e 'my $qs = quotemeta("ssh-rsa AAAA/BBBB/knMQ== user@host.f.q.d.n"); print unless  /^$qs$/ ' '/root/user/b1.bak'
Possible unintended interpolation of @host in string at -e line 1.
Name "main::host" used only once: possible typo at -e line 1.

##</code><code>##

# Direct cli
# perl -w -ni -e 'my $str = sprintf( qq(%s), q(ssh-rsa AAAA/BBBB/knMQ== user@host.f.q.d.n) ); print $_ unless $_ =~ /$str/ '  /root/user/b1.bak


# From within  puppet
command => "/usr/bin/perl -w -ni -e 'my \$str = sprintf( qq(%s), q($line) ); print \$_ unless \$_ =~ /\$str/ ' '${file}'",

##</code><code>##

# cat b1.bak 
ssh-rsa CCCC/DDDD/knMQ== user@host2.f.q.d.n
ssh-rsa AAAA/BBBB/kPW+Yi9yZ7Kh0mL/knMQ== user@host.f.q.d.n

 # perl -w -n -e 'my $str = sprintf( qq(%s), q(ssh-rsa AAAA/BBBB/kPW+Yi9yZ7Kh0mL/knMQ== user@host.f.q.d.n) ); print $_ unless $_ =~ /$str/ '  /root/user/b1.bak
ssh-rsa CCCC/DDDD/knMQ== user@host2.f.q.d.n
ssh-rsa AAAA/BBBB/kPW+Yi9yZ7Kh0mL/knMQ== user@host.f.q.d.n