1 files changed, 24 insertions, 1 deletions
diff --git a/editor/pnmflip b/editor/pnmflip
index 44d95b45..07d4ddb9 100755
--- a/editor/pnmflip
+++ b/editor/pnmflip
@@ -1,5 +1,28 @@
-#!/usr/bin/perl -w
+#!/bin/sh
 
+##############################################################################
+# This is essentially a Perl program.  We exec the Perl interpreter specifying
+# this same file as the Perl program and use the -x option to cause the Perl
+# interpreter to skip down to the Perl code.  The reason we do this instead of
+# just making /usr/bin/perl the script interpreter (instead of /bin/sh) is
+# that the user may have multiple Perl interpreters and the one he wants to
+# use is properly located in the PATH.  The user's choice of Perl interpreter
+# may be crucial, such as when the user also has a PERL5LIB environment
+# variable and it selects modules that work with only a certain main
+# interpreter program.
+#
+# An alternative some people use is to have /usr/bin/env as the script
+# interpreter.  We don't do that because we think the existence and
+# compatibility of /bin/sh is more reliable.
+#
+# Note that we aren't concerned about efficiency because the user who needs
+# high efficiency can use directly the programs that this program invokes.
+#
+##############################################################################
+
+exec perl -w -x -S -- "$0" "$@"
+
+#!/usr/bin/perl
 #============================================================================
 #  This is a compatibility interface to Pamflip.
 #