[demo] Perl and Python backtrack, but POSIX style engines don't.

This was what I expected!

demo/regex-backtrack.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 #
+# Demo for EggEx.  Do any of these common engines backtrack?
+#
 # Usage:
 #   ./regex-backtrack.sh <function name>
 
@@ -47,27 +49,70 @@ egrep-task() {
   local text=$1
   local pattern=$2
 
-  echo -n 'eg '
-  echo "$text" | egrep "$pattern" || true
+  echo -n 'egrep '
+  echo "$text" | egrep "$pattern"
+}
+
+sed-task() {
+  local text=$1
+  local pattern=$2
+
+  echo -n 'sed   '
+  echo "$text" | sed "/$pattern/p"
+}
+
+awk-task() {
+  local bin=$1
+  local text=$2
+  local pattern=$3
+
+  echo -n "$bin  "
+  echo "$text" | $bin "/$pattern/ { print }"
+}
+
+mawk-task() { awk-task mawk "$@"; }
+gawk-task() { awk-task gawk "$@"; }
+
+libc-task() {
+  ### bash is linked against libc
+
+  local text=$1
+  local pattern=$2
+
+  echo -n 'libc  '
+  # note: pattern can't be quoted
+  [[ "$text" =~ $pattern ]] && echo $text
 }
 
 python-task() {
   local text=$1
   local pattern=$2
 
-  echo -n 'py '
+  echo -n 'py    '
   python -c '
 import re, sys
 
 pattern, text = sys.argv[1:]
 #print(pattern)
 #print(text)
+
+# Assumed to match
 print(re.match(pattern, text).group(0))
 ' "$pattern" "$text"
 }
 
+perl-task() {
+  local text=$1
+  local pattern=$2
+
+  echo -n 'perl  '
+  echo "$text" | perl -n -e "print if /$pattern/"
+
+  # https://stackoverflow.com/questions/4794145/perl-one-liner-like-grep
+}
+
 benchmark() {
-  local max=${1:-20}
+  local max=${1:-22}
 
   TIMEFORMAT='%U'  # CPU seconds spent in user mode
 
@@ -76,7 +121,12 @@ benchmark() {
     local text=$(text $i)
 
     time egrep-task "$text" "$pattern"
+    time sed-task "$text" "$pattern"
+    time libc-task "$text" "$pattern"
+    time gawk-task "$text" "$pattern"
+    time mawk-task "$text" "$pattern"
     time python-task "$text" "$pattern"
+    time perl-task "$text" "$pattern"
     echo
   done
 }