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FLEX(1)

📛 NAME

flex - the fast lexical analyser generator

🚀 Quick Reference

Use Case	Command	Description
📄 Compile a lexer file	flex lexer.l	Generate the default C scanner lex.yy.c
📤 Specify output file	flex -o lexer.c lexer.l	Write scanner to lexer.c instead of the default
🧬 Generate C++ scanner	flex -+ lexer.l	Create a C++ scanner class
📋 Produce header file	flex --header-file=lexer.h lexer.l	Generate a C header file alongside the scanner
🐞 Debug mode	flex -d lexer.l	Enable debug output in the generated scanner
🔤 Case‑insensitive scanning	flex -i lexer.l	Ignore case in patterns
🔄 Reentrant scanner	flex -R lexer.l	Generate a reentrant (thread‑safe) C scanner
🤫 Suppress warnings	flex -w lexer.l	Do not generate warning messages

🔍 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
• --hex 🔢 use hexadecimal numbers instead of octal in debug outputs

📁 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
• --backup-file=FILE 💾 write backing‑up information to FILE

⚙️ Scanner Behavior

• -7, --7bit 7️⃣ generate 7‑bit scanner
• -8, --8bit 8️⃣ 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
• --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 ℹ️ 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(1)

📛 NAME 🚀 Quick Reference 🔍 SYNOPSIS 📖 DESCRIPTION 📚 SEE ALSO