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Top Forums Shell Programming and Scripting A Perl regexp to validate arithmetic expressions Post 302478183 by DGPickett on Tuesday 7th of December 2010 10:04:18 AM
Old 12-07-2010
This sort validation is more a bison/lex/flex sort of thing, probably available in PERL, too. A small state machine in C could apply the rules, too, tracking parse state. However, I suspect even the most talented regex writer cannot decode infinitely complex state in a regex. Some things are easier done in stages, too, like parentheses and quote balance. Each milieu comes with it's own rules about what is an escape, how linefeeds are treated, punctuation of just white space.
 

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FLEX(1) 							   User Commands							   FLEX(1)

NAME
flex - the fast lexical analyser generator SYNOPSIS
flex [OPTIONS] [FILE]... DESCRIPTION
Generates programs that perform pattern-matching on text. Table Compression: -Ca, --align trade off larger tables for better memory alignment -Ce, --ecs construct equivalence classes -Cf do not compress tables; use -f representation -CF do not compress tables; use -F representation -Cm, --meta-ecs construct meta-equivalence classes -Cr, --read use read() instead of stdio for scanner input -f, --full generate fast, large scanner. Same as -Cfr -F, --fast use alternate table representation. Same as -CFr -Cem default compression (same as --ecs --meta-ecs) Debugging: -d, --debug enable debug mode in scanner -b, --backup write backing-up information to lex.backup -p, --perf-report write performance report to stderr -s, --nodefault suppress default rule to ECHO unmatched text -T, --trace flex should run in trace mode -w, --nowarn do not generate warnings -v, --verbose write summary of scanner statistics to stdout Files: -o, --outfile=FILE specify output filename -S, --skel=FILE specify skeleton file -t, --stdout write scanner on stdout instead of lex.yy.c --yyclass=NAME name of C++ class --header-file=FILE create a C header file in addition to the scanner --tables-file[=FILE] write tables to FILE Scanner behavior: -7, --7bit generate 7-bit scanner -8, --8bit generate 8-bit scanner -B, --batch generate batch scanner (opposite of -I) -i, --case-insensitive ignore case in patterns -l, --lex-compat maximal compatibility with original lex -X, --posix-compat maximal compatibility with POSIX lex -I, --interactive generate interactive scanner (opposite of -B) --yylineno track line count in yylineno Generated code: -+, --c++ generate C++ scanner class -Dmacro[=defn] #define macro defn (default defn is '1') -L, --noline suppress #line directives in scanner -P, --prefix=STRING use STRING as prefix instead of "yy" -R, --reentrant generate a reentrant C scanner --bison-bridge scanner for bison pure parser. --bison-locations include yylloc support. --stdinit initialize yyin/yyout to stdin/stdout --noansi-definitions old-style function definitions --noansi-prototypes empty parameter list in prototypes --nounistd do not include <unistd.h> --noFUNCTION do not generate a particular FUNCTION Miscellaneous: -c do-nothing POSIX option -n do-nothing POSIX option -? -h, --help produce this help message -V, --version report flex version SEE ALSO
The full documentation for flex is maintained as a Texinfo manual. If the info and flex programs are properly installed at your site, the command info flex should give you access to the complete manual. flex 2.5.35 February 2008 FLEX(1)
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