diff --git a/README.md b/README.md
index bee88f5..8d96bcf 100644
--- a/README.md
+++ b/README.md
@@ -264,3 +264,12 @@ cope here.
 
 `m4` is the first piece of software we need in the autotools suite. It allows
 macros to be defined and files to be generated from those macros.
+
+#### Part 20: flex 2.5.11
+`flex` is a tool for generating lexers or scanners: programs that recognize lexical patters.
+
+Unfortunately `flex` also depends on itself for compiling its own scanner, so
+first flex 2.5.11 is compiled, with its scanner definition manually modified so that
+it can be processed by lex for the Heirloom project (the required modifications
+are mostly syntactical, plus a few workarounds to avoid some flex advanced features).
+Then we recompile `flex` using its own lexer.
diff --git a/rootfs.sh b/rootfs.sh
index d0b5a5c..5ebda98 100755
--- a/rootfs.sh
+++ b/rootfs.sh
@@ -129,6 +129,9 @@ get_file https://ftp.gnu.org/pub/gnu/bash/bash-2.05b.tar.gz
 # m4 1.4
 get_file https://ftp.gnu.org/gnu/m4/m4-1.4.tar.gz
 
+# flex 2.5.11
+get_file http://download.nust.na/pub2/openpkg1/sources/DST/flex/flex-2.5.11.tar.gz
+
 # General cleanup
 find tmp -name .git -exec rm -rf \;
 
diff --git a/sysa/flex-2.5.11/files/scan.lex.l b/sysa/flex-2.5.11/files/scan.lex.l
new file mode 100644
index 0000000..e0273d7
--- /dev/null
+++ b/sysa/flex-2.5.11/files/scan.lex.l
@@ -0,0 +1,712 @@
+/* scan.l - scanner for flex input -*-C-*- */
+
+%{
+/*  Copyright (c) 1990 The Regents of the University of California. */
+/*  All rights reserved. */
+
+/*  This code is derived from software contributed to Berkeley by */
+/*  Vern Paxson. */
+
+/*  The United States Government has rights in this work pursuant */
+/*  to contract no. DE-AC03-76SF00098 between the United States */
+/*  Department of Energy and the University of California. */
+
+/*  This file is part of flex. */
+
+/*  Redistribution and use in source and binary forms, with or without */
+/*  modification, are permitted provided that the following conditions */
+/*  are met: */
+
+/*  1. Redistributions of source code must retain the above copyright */
+/*     notice, this list of conditions and the following disclaimer. */
+/*  2. Redistributions in binary form must reproduce the above copyright */
+/*     notice, this list of conditions and the following disclaimer in the */
+/*     documentation and/or other materials provided with the distribution. */
+
+/*  Neither the name of the University nor the names of its contributors */
+/*  may be used to endorse or promote products derived from this software */
+/*  without specific prior written permission. */
+
+/*  THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR */
+/*  IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED */
+/*  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR */
+/*  PURPOSE. */
+
+#define yyin_defined
+#include "flexdef.h"
+#include "parse.h"
+
+#define ACTION_ECHO add_action( yytext )
+#define ACTION_IFDEF(def, should_define) \
+	{ \
+	if ( should_define ) \
+		action_define( def, 1 ); \
+	}
+
+#define MARK_END_OF_PROLOG mark_prolog();
+
+#define YY_DECL \
+	int flexscan()
+
+#define RETURNCHAR \
+	yylval = (unsigned char) yytext[0]; \
+	return CHAR;
+
+#define RETURNNAME \
+	strcpy( nmstr, yytext ); \
+	return NAME;
+
+#define PUT_BACK_STRING(str, start) \
+	for ( i = strlen( str ) - 1; i >= start; --i ) \
+		unput((str)[i])
+
+#define CHECK_REJECT(str) \
+	if ( all_upper( str ) ) \
+		reject = true;
+
+#define CHECK_YYMORE(str) \
+	if ( all_lower( str ) ) \
+		yymore_used = true;
+
+#define YY_USER_INIT \
+	if ( getenv("POSIXLY_CORRECT") ) \
+		posix_compat = true;
+
+#ifndef yy_set_bol
+#define yy_set_bol(x) (x ? NLSTATE : 0)
+#endif
+
+#define YY_NULL 0
+#define yyterminate() return YY_NULL
+
+%}
+
+%e 5000
+%p 10000
+%a 100000
+%n 5000
+
+%x SECT2 SECT2PROLOG SECT3 CODEBLOCK PICKUPDEF SC CARETISBOL NUM QUOTE
+%x FIRSTCCL CCL ACTION RECOVER COMMENT ACTION_STRING
+%x OPTION LINEDIR
+
+WS		[ \t]+
+OPTWS		[ \t]*
+NOT_WS		[^ \t\r\n]
+
+NL		\r?\n
+
+NAME		([a-zA-Z_][a-zA-Z0-9_-]*)
+NOT_NAME	[^a-zA-Z_*\n]+
+
+SCNAME		{NAME}
+
+ESCSEQ		(\\([^\n]|[0-7]{1,3}|x[0-9a-fA-F]{1,2}))
+
+FIRST_CCL_CHAR	([^\\\n]|{ESCSEQ})
+CCL_CHAR	([^\\\n\]]|{ESCSEQ})
+CCL_EXPR	("[:"[a-zA-Z]+":]")
+
+LEXOPT		[aceknopr]
+
+%%
+	static int bracelevel, didadef, indented_code;
+	static int doing_rule_action = false;
+	static int option_sense;
+
+	int doing_codeblock = false;
+	int i;
+	Char nmdef[MAXLINE];
+
+
+<INITIAL>^{WS}		{ indented_code = true; BEGIN(CODEBLOCK); }
+<INITIAL>^"/*"		{ ACTION_ECHO; BEGIN( COMMENT ); }
+<INITIAL>^#{OPTWS}line{WS}	{ BEGIN( LINEDIR ); }
+<INITIAL>^"%s"{NAME}?	{ return SCDECL; }
+<INITIAL>^"%x"{NAME}?	{ return XSCDECL; }
+<INITIAL>^"%{".*{NL}	{
+			++linenum;
+			line_directive_out( (FILE *) 0, 1 );
+			indented_code = false;
+			BEGIN(CODEBLOCK);
+			}
+
+<INITIAL>{WS}		{ /* discard */ }
+
+<INITIAL>^"%%".*		{
+			sectnum = 2;
+			bracelevel = 0;
+			mark_defs1();
+			line_directive_out( (FILE *) 0, 1 );
+			BEGIN(SECT2PROLOG);
+			return SECTEND;
+			}
+
+<INITIAL>^"%pointer".*{NL}	{ yytext_is_array = false; ++linenum; }
+<INITIAL>^"%array".*{NL}		{ yytext_is_array = true; ++linenum; }
+
+<INITIAL>^"%option"	{ BEGIN(OPTION); return OPTION_OP; }
+
+<INITIAL>^"%"{LEXOPT}{OPTWS}[0-9]*{OPTWS}{NL}	{ ++linenum; /* ignore */ }
+<INITIAL>^"%"{LEXOPT}{WS}.*{NL}	{ ++linenum;	/* ignore */ }
+
+<INITIAL>^"%"[^sxaceknopr{}].*	{ synerr( _( "unrecognized '%' directive" ) ); }
+
+<INITIAL>^{NAME}		{
+			strcpy( nmstr, yytext );
+			didadef = false;
+			BEGIN(PICKUPDEF);
+			}
+
+<INITIAL>{SCNAME}	{ RETURNNAME; }
+<INITIAL>^{OPTWS}{NL}	{ ++linenum; /* allows blank lines in section 1 */ }
+<INITIAL>{OPTWS}{NL}	{ ACTION_ECHO; ++linenum; /* maybe end of comment line */ }
+
+
+<COMMENT>"*/"		{ ACTION_ECHO; BEGIN(INITIAL); }
+<COMMENT>"*"		{ ACTION_ECHO; }
+<COMMENT>[^*\n]+		{ ACTION_ECHO; }
+<COMMENT>[^*\n]*{NL}	{ ++linenum; ACTION_ECHO; }
+
+<LINEDIR>\n		{ BEGIN(INITIAL); }
+<LINEDIR>[0-9]+	{ linenum = myctoi( yytext ); }
+
+<LINEDIR>\"[^"\n]*\"	{
+			flex_free( (void *) infilename );
+			infilename = copy_string( yytext + 1 );
+			infilename[strlen( infilename ) - 1] = '\0';
+			}
+
+<CODEBLOCK>^"%}".*{NL}	{ ++linenum; BEGIN(INITIAL); }
+
+<CODEBLOCK>{NAME}|{NOT_NAME}|.	{ ACTION_ECHO; }
+
+<CODEBLOCK>{NL}		{
+			++linenum;
+			ACTION_ECHO;
+			if ( indented_code )
+				BEGIN(INITIAL);
+			}
+
+
+<PICKUPDEF>{WS}		{ /* separates name and definition */ }
+
+<PICKUPDEF>{NOT_WS}[^\r\n]*	{
+			strcpy( (char *) nmdef, yytext );
+
+			/* Skip trailing whitespace. */
+			for ( i = strlen( (char *) nmdef ) - 1;
+			      i >= 0 && (nmdef[i] == ' ' || nmdef[i] == '\t');
+			      --i )
+				;
+
+			nmdef[i + 1] = '\0';
+
+			ndinstal( nmstr, nmdef );
+			didadef = true;
+			}
+
+<PICKUPDEF>{NL}		{
+			if ( ! didadef )
+				synerr( _( "incomplete name definition" ) );
+			BEGIN(INITIAL);
+			++linenum;
+			}
+
+
+<OPTION>{NL}		{ ++linenum; BEGIN(INITIAL); }
+<OPTION>{WS}		{ option_sense = true; }
+
+<OPTION>"="		{ return '='; }
+
+<OPTION>no		{ option_sense = ! option_sense; }
+
+<OPTION>7bit		{ csize = option_sense ? 128 : 256; }
+<OPTION>8bit		{ csize = option_sense ? 256 : 128; }
+
+<OPTION>align		{ long_align = option_sense; }
+<OPTION>always-interactive	{
+			action_define( "YY_ALWAYS_INTERACTIVE", option_sense );
+			}
+<OPTION>array		{ yytext_is_array = option_sense; }
+<OPTION>backup		{ backing_up_report = option_sense; }
+<OPTION>batch		{ interactive = ! option_sense; }
+<OPTION>"c++"		{ C_plus_plus = option_sense; }
+<OPTION>caseful|case-sensitive		{ caseins = ! option_sense; }
+<OPTION>caseless|case-insensitive	{ caseins = option_sense; }
+<OPTION>debug		{ ddebug = option_sense; }
+<OPTION>default		{ spprdflt = ! option_sense; }
+<OPTION>ecs		{ useecs = option_sense; }
+<OPTION>fast		{
+			useecs = usemecs = false;
+			use_read = fullspd = true;
+			}
+<OPTION>full		{
+			useecs = usemecs = false;
+			use_read = fulltbl = true;
+			}
+<OPTION>input		{ ACTION_IFDEF("YY_NO_INPUT", ! option_sense); }
+<OPTION>interactive	{ interactive = option_sense; }
+<OPTION>lex-compat	{ lex_compat = option_sense; }
+<OPTION>posix-compat	{ posix_compat = option_sense; }
+<OPTION>main		{
+			action_define( "YY_MAIN", option_sense );
+            /* Override yywrap */
+            if( option_sense == true )
+                do_yywrap = false;
+			}
+<OPTION>meta-ecs	{ usemecs = option_sense; }
+<OPTION>never-interactive	{
+			action_define( "YY_NEVER_INTERACTIVE", option_sense );
+			}
+<OPTION>perf-report	{ performance_report += option_sense ? 1 : -1; }
+<OPTION>pointer		{ yytext_is_array = ! option_sense; }
+<OPTION>read		{ use_read = option_sense; }
+<OPTION>reentrant   { reentrant = option_sense; }
+<OPTION>reentrant-bison {
+                /* reentrant-bison implies reentrant. */
+                if ((reentrant_bison_pure = option_sense) != 0)
+                    reentrant = 1;
+            }    
+<OPTION>reject		{ reject_really_used = option_sense; }
+<OPTION>stack		{ action_define( "YY_STACK_USED", option_sense ); }
+<OPTION>stdinit		{ do_stdinit = option_sense; }
+<OPTION>stdout		{ use_stdout = option_sense; }
+<OPTION>unistd      { ACTION_IFDEF("YY_NO_UNISTD_H", ! option_sense); }
+<OPTION>unput		{ ACTION_IFDEF("YY_NO_UNPUT", ! option_sense); }
+<OPTION>verbose		{ printstats = option_sense; }
+<OPTION>warn		{ nowarn = ! option_sense; }
+<OPTION>yylineno	{ do_yylineno = option_sense; ACTION_IFDEF("YY_USE_LINENO", option_sense); }
+<OPTION>yymore		{ yymore_really_used = option_sense; }
+<OPTION>yywrap      { do_yywrap = option_sense; }
+
+<OPTION>yy_push_state	{ ACTION_IFDEF("YY_NO_PUSH_STATE", ! option_sense); }
+<OPTION>yy_pop_state	{ ACTION_IFDEF("YY_NO_POP_STATE", ! option_sense); }
+<OPTION>yy_top_state	{ ACTION_IFDEF("YY_NO_TOP_STATE", ! option_sense); }
+
+<OPTION>yy_scan_buffer	{ ACTION_IFDEF("YY_NO_SCAN_BUFFER", ! option_sense); }
+<OPTION>yy_scan_bytes	{ ACTION_IFDEF("YY_NO_SCAN_BYTES", ! option_sense); }
+<OPTION>yy_scan_string	{ ACTION_IFDEF("YY_NO_SCAN_STRING", ! option_sense); }
+
+<OPTION>yyalloc         { ACTION_IFDEF("YY_NO_FLEX_ALLOC", ! option_sense); }
+<OPTION>yyrealloc       { ACTION_IFDEF("YY_NO_FLEX_REALLOC", ! option_sense); }
+<OPTION>yyfree          { ACTION_IFDEF("YY_NO_FLEX_FREE", ! option_sense); }
+
+<OPTION>yyget_debug     { ACTION_IFDEF("YY_NO_GET_DEBUG", ! option_sense); }
+<OPTION>yyset_debug     { ACTION_IFDEF("YY_NO_SET_DEBUG", ! option_sense); }
+<OPTION>yyget_extra     { ACTION_IFDEF("YY_NO_GET_EXTRA", ! option_sense); }
+<OPTION>yyset_extra     { ACTION_IFDEF("YY_NO_SET_EXTRA", ! option_sense); }
+<OPTION>yyget_leng      { ACTION_IFDEF("YY_NO_GET_LENG", ! option_sense); }
+<OPTION>yyget_text      { ACTION_IFDEF("YY_NO_GET_TEXT", ! option_sense); }
+<OPTION>yyget_lineno    { ACTION_IFDEF("YY_NO_GET_LINENO", ! option_sense); }
+<OPTION>yyset_lineno    { ACTION_IFDEF("YY_NO_SET_LINENO", ! option_sense); }
+<OPTION>yyget_in        { ACTION_IFDEF("YY_NO_GET_IN", ! option_sense); }
+<OPTION>yyset_in        { ACTION_IFDEF("YY_NO_SET_IN", ! option_sense); }
+<OPTION>yyget_out       { ACTION_IFDEF("YY_NO_GET_OUT", ! option_sense); }
+<OPTION>yyset_out       { ACTION_IFDEF("YY_NO_SET_OUT", ! option_sense); }
+<OPTION>yyget_lval      { ACTION_IFDEF("YY_NO_GET_LVAL", ! option_sense); }
+<OPTION>yyset_lval      { ACTION_IFDEF("YY_NO_SET_LVAL", ! option_sense); }
+<OPTION>yyget_lloc      { ACTION_IFDEF("YY_NO_GET_LLOC", ! option_sense); }
+<OPTION>yyset_lloc      { ACTION_IFDEF("YY_NO_SET_LLOC", ! option_sense); }
+
+<OPTION>outfile		{ return OPT_OUTFILE; }
+<OPTION>prefix		{ return OPT_PREFIX; }
+<OPTION>yyclass		{ return OPT_YYCLASS; }
+<OPTION>header      { return OPT_HEADER; }
+
+<OPTION>\"[^"\n]*\"	{
+			strcpy( nmstr, yytext + 1 );
+			nmstr[strlen( nmstr ) - 1] = '\0';
+			return NAME;
+			}
+
+<OPTION>(([a-mo-z]|n[a-np-z])[a-zA-Z\-+]*)|.	{
+			format_synerr( _( "unrecognized %%option: %s" ),
+				yytext );
+			BEGIN(RECOVER);
+			}
+
+<RECOVER>.*{NL}		{ ++linenum; BEGIN(INITIAL); }
+
+
+<SECT2PROLOG>^"%{".*	{ ++bracelevel; yyless( 2 ); }
+<SECT2PROLOG>^"%}".*	{ --bracelevel; yyless( 2 ); }
+
+<SECT2PROLOG>^{WS}.*	{ ACTION_ECHO;	/* indented code in prolog */ }
+
+<SECT2PROLOG>^{NOT_WS}.*	{	/* non-indented code */
+			if ( bracelevel <= 0 )
+				{ /* not in %{ ... %} */
+				yyless( 0 );	/* put it all back */
+				yy_set_bol( 1 );
+				mark_prolog();
+				BEGIN(SECT2);
+				}
+			else
+				ACTION_ECHO;
+			}
+
+<SECT2PROLOG>.*		{ ACTION_ECHO; }
+<SECT2PROLOG>{NL}	{ ++linenum; ACTION_ECHO; }
+
+<SECT2PROLOG><<EOF>>		{
+			mark_prolog();
+			sectnum = 0;
+			yyterminate(); /* to stop the parser */
+			}
+
+<SECT2>^{OPTWS}{NL}	{ ++linenum; /* allow blank lines in section 2 */ }
+
+<SECT2>^{OPTWS}"%{"	{
+			indented_code = false;
+			doing_codeblock = true;
+			bracelevel = 1;
+                        synerr(_("percent brace action unsupported"));
+			}
+
+<SECT2>^{OPTWS}"<"	{ BEGIN(SC); return '<'; }
+<SECT2>^{OPTWS}"^"	{ return '^'; }
+<SECT2>\"		{ BEGIN(QUOTE); return '"'; }
+<SECT2>"{"/[0-9]	{
+			BEGIN(NUM);
+			if ( lex_compat || posix_compat )
+				return BEGIN_REPEAT_POSIX;
+			else
+				return BEGIN_REPEAT_FLEX;
+			}
+<SECT2>"$"/([ \t]|{NL})	{ return '$'; }
+
+<SECT2>{WS}"%{"		{
+			bracelevel = 1;
+                        synerr(_("percent brace unsupported"));
+
+			if ( in_rule )
+				{
+				doing_rule_action = true;
+				in_rule = false;
+				return '\n';
+				}
+			}
+<SECT2>{WS}"|".*{NL}	{ continued_action = true; ++linenum; return '\n'; }
+
+<SECT2>^{WS}"/*"	{
+			yyless( yyleng - 2 );	/* put back '/', '*' */
+			bracelevel = 0;
+			continued_action = false;
+			BEGIN(ACTION);
+			}
+
+<SECT2>^{WS}		{ /* allow indented rules */ }
+
+<SECT2>{WS}		{
+			/* This rule is separate from the one below because
+			 * otherwise we get variable trailing context, so
+			 * we can't build the scanner using -{f,F}.
+			 */
+			bracelevel = 0;
+			continued_action = false;
+			BEGIN(ACTION);
+
+			if ( in_rule )
+				{
+				doing_rule_action = true;
+				in_rule = false;
+				return '\n';
+				}
+			}
+
+<SECT2>{OPTWS}{NL}	{
+			bracelevel = 0;
+			continued_action = false;
+			BEGIN(ACTION);
+			unput( '\n' );	/* so <ACTION> sees it */
+
+			if ( in_rule )
+				{
+				doing_rule_action = true;
+				in_rule = false;
+				return '\n';
+				}
+			}
+
+<SECT2>^{OPTWS}"<<EOF>>"	|
+<SECT2>"<<EOF>>"	{ return EOF_OP; }
+
+<SECT2>^"%%".*		{
+			sectnum = 3;
+			BEGIN(SECT3);
+			outn("/* Begin user sect3 */");
+			yyterminate(); /* to stop the parser */
+			}
+
+<SECT2>"["({FIRST_CCL_CHAR}|{CCL_EXPR})({CCL_CHAR}|{CCL_EXPR})*	{
+			int cclval;
+
+			strcpy( nmstr, yytext );
+
+			/* Check to see if we've already encountered this
+			 * ccl.
+			 */
+			if ( (cclval = ccllookup( (Char *) nmstr )) != 0 )
+				{
+				if ( input() != ']' )
+					synerr( _( "bad character class" ) );
+
+				yylval = cclval;
+				++cclreuse;
+				return PREVCCL;
+				}
+			else
+				{
+				/* We fudge a bit.  We know that this ccl will
+				 * soon be numbered as lastccl + 1 by cclinit.
+				 */
+				cclinstal( (Char *) nmstr, lastccl + 1 );
+
+				/* Push back everything but the leading bracket
+				 * so the ccl can be rescanned.
+				 */
+				yyless( 1 );
+
+				BEGIN(FIRSTCCL);
+				return '[';
+				}
+			}
+
+<SECT2>"{"{NAME}"}"[ \t\n\f\r\v]?	 {
+			register Char *nmdefptr;
+            int end_is_ws, end_ch;
+            
+            end_ch = yytext[yyleng-1];
+            end_is_ws = end_ch != '}' ? 1 : 0;
+
+			strcpy( nmstr, yytext + 1 );
+			nmstr[yyleng - 2 - end_is_ws] = '\0';  /* chop trailing brace */
+
+			if ( (nmdefptr = ndlookup( nmstr )) == 0 )
+				format_synerr(
+					_( "undefined definition {%s}" ),
+						nmstr );
+
+			else
+				{ /* push back name surrounded by ()'s */
+				int len = strlen( (char *) nmdefptr );
+                if (end_is_ws)
+                    unput(end_ch);
+
+				if ( lex_compat || nmdefptr[0] == '^' ||
+				     (len > 0 && nmdefptr[len - 1] == '$')
+                     || end_is_ws)
+					{ /* don't use ()'s after all */
+					PUT_BACK_STRING((char *) nmdefptr, 0);
+
+					if ( nmdefptr[0] == '^' )
+						BEGIN(CARETISBOL);
+					}
+
+				else
+					{
+					unput(')');
+					PUT_BACK_STRING((char *) nmdefptr, 0);
+					unput('(');
+					}
+				}
+			}
+
+<SECT2>[/|*+?.(){}]	{ return (unsigned char) yytext[0]; }
+<SECT2>.		{ RETURNCHAR; }
+
+
+<SC>{OPTWS}{NL}{OPTWS}	{ ++linenum;	/* Allow blank lines & continuations */ }
+<SC>[,*]		{ return (unsigned char) yytext[0]; }
+<SC>">"		{ BEGIN(SECT2); return '>'; }
+<SC>">"/^		{ BEGIN(CARETISBOL); return '>'; }
+<SC>{SCNAME}	{ RETURNNAME; }
+<SC>.		{
+			format_synerr( _( "bad <start condition>: %s" ),
+				yytext );
+			}
+
+<CARETISBOL>"^"		{ BEGIN(SECT2); return '^'; }
+
+
+<QUOTE>[^"\n]		{ RETURNCHAR; }
+<QUOTE>\"		{ BEGIN(SECT2); return '"'; }
+
+<QUOTE>{NL}		{
+			synerr( _( "missing quote" ) );
+			BEGIN(SECT2);
+			++linenum;
+			return '"';
+			}
+
+
+<FIRSTCCL>"^"/[^\]\n-]	{ BEGIN(CCL); return '^'; }
+<FIRSTCCL>"^"/("-"|"]")	{ return '^'; }
+<FIRSTCCL>.		{ BEGIN(CCL); RETURNCHAR; }
+
+<CCL>-/[^\]\n]	{ return '-'; }
+<CCL>[^\]\n]		{ RETURNCHAR; }
+<CCL>"]"		{ BEGIN(SECT2); return ']'; }
+<CCL>.|{NL}		{
+			synerr( _( "bad character class" ) );
+			BEGIN(SECT2);
+			return ']';
+			}
+
+<FIRSTCCL,CCL>"[:alnum:]"	{ BEGIN(CCL); return CCE_ALNUM; }
+<FIRSTCCL,CCL>"[:alpha:]"	{ BEGIN(CCL); return CCE_ALPHA; }
+<FIRSTCCL,CCL>"[:blank:]"	{ BEGIN(CCL); return CCE_BLANK; }
+<FIRSTCCL,CCL>"[:cntrl:]"	{ BEGIN(CCL); return CCE_CNTRL; }
+<FIRSTCCL,CCL>"[:digit:]"	{ BEGIN(CCL); return CCE_DIGIT; }
+<FIRSTCCL,CCL>"[:graph:]"	{ BEGIN(CCL); return CCE_GRAPH; }
+<FIRSTCCL,CCL>"[:lower:]"	{ BEGIN(CCL); return CCE_LOWER; }
+<FIRSTCCL,CCL>"[:print:]"	{ BEGIN(CCL); return CCE_PRINT; }
+<FIRSTCCL,CCL>"[:punct:]"	{ BEGIN(CCL); return CCE_PUNCT; }
+<FIRSTCCL,CCL>"[:space:]"	{ BEGIN(CCL); return CCE_SPACE; }
+<FIRSTCCL,CCL>"[:upper:]"	{ BEGIN(CCL); return CCE_UPPER; }
+<FIRSTCCL,CCL>"[:xdigit:]"	{ BEGIN(CCL); return CCE_XDIGIT; }
+<FIRSTCCL,CCL>{CCL_EXPR}	{
+			format_synerr(
+				_( "bad character class expression: %s" ),
+					yytext );
+			BEGIN(CCL); return CCE_ALNUM;
+			}
+
+<NUM>[0-9]+	{
+			yylval = myctoi( yytext );
+			return NUMBER;
+			}
+
+<NUM>","		{ return ','; }
+<NUM>"}"		{
+			BEGIN(SECT2);
+			if ( lex_compat || posix_compat )
+				return END_REPEAT_POSIX;
+			else
+				return END_REPEAT_FLEX;
+			}
+
+<NUM>.		{
+			synerr( _( "bad character inside {}'s" ) );
+			BEGIN(SECT2);
+			return '}';
+			}
+
+<NUM>{NL}		{
+			synerr( _( "missing }" ) );
+			BEGIN(SECT2);
+			++linenum;
+			return '}';
+			}
+
+
+
+<ACTION>"{"		{ ACTION_ECHO; ++bracelevel; }
+<ACTION>"}"		{ ACTION_ECHO; --bracelevel; }
+<ACTION>[^a-zA-Z_\{\}\"'/\n]+	{ ACTION_ECHO; }
+<ACTION>{NAME}		{ ACTION_ECHO; }
+<ACTION>"'"([^'\\\n]|\\.)*"'"	{ ACTION_ECHO; /* character constant */ }
+<ACTION>\"		{ ACTION_ECHO; BEGIN(ACTION_STRING); }
+<ACTION>{NL}		{
+			++linenum;
+			ACTION_ECHO;
+			if ( bracelevel == 0 )
+				{
+				if ( doing_rule_action )
+					add_action( "\tYY_BREAK\n" );
+
+				doing_rule_action = false;
+				BEGIN(SECT2);
+				}
+			}
+<ACTION>.		{ ACTION_ECHO; }
+
+<ACTION_STRING>[^"\\\n]+	{ ACTION_ECHO; }
+<ACTION_STRING>\\.		{ ACTION_ECHO; }
+<ACTION_STRING>{NL}		{ ++linenum; ACTION_ECHO; BEGIN(ACTION); }
+<ACTION_STRING>\"		{ ACTION_ECHO; BEGIN(ACTION); }
+<ACTION_STRING>.		{ ACTION_ECHO; }
+
+<COMMENT,ACTION,ACTION_STRING><<EOF>>	{
+			synerr( _( "EOF encountered inside an action" ) );
+			yyterminate();
+			}
+
+
+<SECT2,QUOTE,FIRSTCCL,CCL>{ESCSEQ}	{
+			yylval = myesc( (Char *) yytext );
+
+			if ( YYSTATE == FIRSTCCL )
+				BEGIN(CCL);
+
+			return CHAR;
+			}
+
+
+<SECT3>.*(\n?)		{ ECHO; }
+<SECT3><<EOF>>		{ sectnum = 0; yyterminate(); }
+
+.|\n                        { format_synerr( _( "bad character: %s" ), yytext ); }
+
+%%
+
+
+int yywrap()
+	{
+	if ( --num_input_files > 0 )
+		{
+		set_input_file( *++input_files );
+		return 0;
+		}
+
+	else
+		return 1;
+	}
+
+
+/* set_input_file - open the given file (if NULL, stdin) for scanning */
+
+void set_input_file( file )
+char *file;
+	{
+	if ( file && strcmp( file, "-" ) )
+		{
+		infilename = copy_string( file );
+		yyin = fopen( infilename, "r" );
+
+		if ( yyin == NULL )
+			lerrsf( _( "can't open %s" ), file );
+		}
+
+	else
+		{
+		yyin = stdin;
+		infilename = copy_string( "<stdin>" );
+		}
+
+	linenum = 1;
+	}
+
+
+/* Wrapper routines for accessing the scanner's malloc routines. */
+
+void *flex_alloc( size )
+size_t size;
+	{
+	return (void *) malloc( size );
+	}
+
+void *flex_realloc( ptr, size )
+void *ptr;
+size_t size;
+	{
+	return (void *) realloc( ptr, size );
+	}
+
+void flex_free( ptr )
+void *ptr;
+	{
+	if ( ptr )
+		free( ptr );
+	}
diff --git a/sysa/flex-2.5.11/flex-2.5.11.sh b/sysa/flex-2.5.11/flex-2.5.11.sh
new file mode 100755
index 0000000..e96a2ce
--- /dev/null
+++ b/sysa/flex-2.5.11/flex-2.5.11.sh
@@ -0,0 +1,22 @@
+# When we rebuild flex it no longer needs patching
+# and can use simplified makefile
+src_prepare() {
+    if test -d /lex; then
+        default_src_prepare
+    else
+        cp ../../mk/main2.mk Makefile
+    fi
+    touch config.h
+    rm parse.c parse.h scan.c
+}
+
+src_install() {
+    if test -d /lex; then
+        # Remove lex, later  make install will symlink lex to flex
+        rm -rf /lex
+        rm -f "${PREFIX}/bin/lex"
+        rm -f "${PREFIX}/lib/libl.a"
+    fi
+    
+    default_src_install
+}
diff --git a/sysa/flex-2.5.11/mk/main.mk b/sysa/flex-2.5.11/mk/main.mk
new file mode 100644
index 0000000..528925f
--- /dev/null
+++ b/sysa/flex-2.5.11/mk/main.mk
@@ -0,0 +1,37 @@
+CFLAGS = -DVERSION=\"2.5.11\"
+
+all: flex
+
+flex: ccl.o dfa.o ecs.o gen.o main.o misc.o nfa.o parse.o scan.o skel.o sym.o tblcmp.o yylex.o options.o scanopt.o buf.o
+	tcc -o $@ $^ -ll
+
+flex-tmp: ccl.o dfa.o ecs.o gen.o main.o misc.o nfa.o parse.o scan-tmp.o skel.o sym.o tblcmp.o yylex.o options.o scanopt.o buf.o
+	tcc -o $@ $^ -ll
+
+%.o: %.c
+	tcc -g -c $(CFLAGS) -o $@ $<
+
+scan.o: parse.h
+scan-tmp.o: parse.h
+yylex.o: parse.h
+
+parse.c parse.h: parse.y
+	yacc -d parse.y
+	mv y.tab.h parse.h
+	mv y.tab.c parse.c
+
+scan-tmp.c: scan.lex.l
+	lex scan.lex.l
+	sed 's|yylex|flexscan|g' -i lex.yy.c
+	mv lex.yy.c scan-tmp.c
+
+scan.c: scan.l flex-tmp
+	./flex-tmp scan.l
+	mv lex.yy.c scan.c
+
+skel.c: mkskel.sh flex.skl
+	/bin/sh ./mkskel.sh ./flex.skl > skel.c
+
+install: all
+	install flex $(PREFIX)/bin
+	ln -sf $(PREFIX)/bin/flex $(PREFIX)/bin/lex
diff --git a/sysa/flex-2.5.11/mk/main2.mk b/sysa/flex-2.5.11/mk/main2.mk
new file mode 100644
index 0000000..0f33808
--- /dev/null
+++ b/sysa/flex-2.5.11/mk/main2.mk
@@ -0,0 +1,28 @@
+CFLAGS = -DVERSION=\"2.5.11\"
+
+all: flex
+
+flex: ccl.o dfa.o ecs.o gen.o main.o misc.o nfa.o parse.o scan.o skel.o sym.o tblcmp.o yylex.o options.o scanopt.o buf.o
+	tcc -o $@ $^
+
+%.o: %.c
+	tcc -g -c $(CFLAGS) -o $@ $<
+
+scan.o: parse.h
+yylex.o: parse.h
+
+parse.c parse.h: parse.y
+	yacc -d parse.y
+	mv y.tab.h parse.h
+	mv y.tab.c parse.c
+
+scan.c: scan.l
+	flex scan.l
+	mv lex.yy.c scan.c
+
+skel.c: mkskel.sh flex.skl
+	/bin/sh ./mkskel.sh ./flex.skl > skel.c
+
+install: all
+	install flex $(PREFIX)/bin
+	ln -sf $(PREFIX)/bin/flex $(PREFIX)/bin/lex
diff --git a/sysa/flex-2.5.11/patches/flexdef.patch b/sysa/flex-2.5.11/patches/flexdef.patch
new file mode 100644
index 0000000..e4f68d4
--- /dev/null
+++ b/sysa/flex-2.5.11/patches/flexdef.patch
@@ -0,0 +1,24 @@
+diff --git flexdef.h flexdef.h
+index 3eb710a..94ef024 100644
+--- flexdef.h
++++ flexdef.h
+@@ -421,7 +421,7 @@ extern int yymore_really_used, reject_really_used;
+  */
+ 
+ extern int datapos, dataline, linenum, out_linenum;
+-extern FILE *skelfile, *yyin, *backing_up_file;
++extern FILE *skelfile, *backing_up_file;
+ extern const char *skel[];
+ extern int skel_ind;
+ extern char *infilename, *outfilename, *headerfilename;
+@@ -432,6 +432,10 @@ extern char **input_files;
+ extern int num_input_files;
+ extern char *program_name;
+ 
++#ifndef yyin_defined
++extern FILE* yyin;
++#endif
++
+ extern char *action_array;
+ extern int action_size;
+ extern int defs1_offset, prolog_offset, action_offset, action_index;
diff --git a/sysa/flex-2.5.11/patches/scan_l.patch b/sysa/flex-2.5.11/patches/scan_l.patch
new file mode 100644
index 0000000..0761543
--- /dev/null
+++ b/sysa/flex-2.5.11/patches/scan_l.patch
@@ -0,0 +1,36 @@
+diff --git scan.l scan.l
+index 18d0de8..c251a5e 100644
+--- scan.l
++++ scan.l
+@@ -32,6 +32,7 @@
+ /*  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR */
+ /*  PURPOSE. */
+ 
++#define yyin_defined
+ #include "flexdef.h"
+ #include "parse.h"
+ 
+@@ -334,8 +335,8 @@ LEXOPT		[aceknopr]
+ 
+ 
+ <SECT2PROLOG>{
+-	^"%{".*	++bracelevel; yyless( 2 );	/* eat only %{ */
+-	^"%}".*	--bracelevel; yyless( 2 );	/* eat only %} */
++	^"%{".*	++bracelevel; yyless( 2 );
++	^"%}".*	--bracelevel; yyless( 2 );
+ 
+ 	^{WS}.*	ACTION_ECHO;	/* indented code in prolog */
+ 
+@@ -480,11 +481,11 @@ LEXOPT		[aceknopr]
+ 				}
+ 			}
+ 
++	"{"{NAME}"}"[[:space:]]?	 {
+     /* Check for :space: at the end of the rule so we don't
+      * wrap the expanded regex in '(' ')' -- breaking trailing
+      * context.
+      */
+-	"{"{NAME}"}"[[:space:]]?	 {
+ 			register Char *nmdefptr;
+             int end_is_ws, end_ch;
+             
diff --git a/sysa/flex-2.5.11/src/.placeholder b/sysa/flex-2.5.11/src/.placeholder
new file mode 100644
index 0000000..e69de29
diff --git a/sysa/helpers.sh b/sysa/helpers.sh
index 6cd9292..e9d160d 100755
--- a/sysa/helpers.sh
+++ b/sysa/helpers.sh
@@ -16,10 +16,11 @@ build () {
     script_name=${2:-${pkg}.sh}
 
     cd "$pkg" || (echo "Cannot cd into ${pkg}!"; kill $$)
-    echo "${pkg}: beginning build"
+    echo "${pkg}: beginning build using script ${script_name}"
     base_dir="${PWD}"
     patch_dir="${base_dir}/patches"
     mk_dir="${base_dir}/mk"
+    files_dir="${base_dir}/files"
 
     rm -rf "build"
     mkdir -p "build"
@@ -74,7 +75,7 @@ default_src_unpack() {
 
 # Default function to prepare source code.
 # It applies all patches from patch_dir (at the moment only -p0 patches are supported).
-# Then it copies our custom makefile.
+# Then it copies our custom makefile and any other custom files from files directory.
 default_src_prepare() {
     if test -d "${patch_dir}"; then
         for p in "${patch_dir}"/*.patch; do
@@ -86,6 +87,10 @@ default_src_prepare() {
     if test -e "${makefile}"; then
         cp "${makefile}" Makefile
     fi
+
+    if test -d "${files_dir}"; then
+        cp "${files_dir}"/* "${PWD}/"
+    fi
 }
 
 # Default function for configuring source.
diff --git a/sysa/run.sh b/sysa/run.sh
index 76095f8..d5ecd18 100755
--- a/sysa/run.sh
+++ b/sysa/run.sh
@@ -12,4 +12,8 @@ export PREFIX=/after
 # Part 21
 build m4-1.4
 
+# Part 22
+build flex-2.5.11
+build flex-2.5.11
+
 echo "Bootstrapping completed."