fstunion(1)

💖 fstunion — the manual, but make it make sense 💖

okay bestie, so this is fstunion, a User Commands page, and it does exactly one (1) iconic thing: it smashes two FSTs together into their union. that's it. that's the whole job. but she has options, and we're gonna go through every single one because we don't skip. periodt. 🎀

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✨ NAME ✨

fstunion — create the union of two FSTs 🦋

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🌸 SYNOPSIS 🌸

fstunion [OPTIONS] in1.fst in2.fst [out.fst]

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💅 DESCRIPTION 💅

Creates the union of two FSTs. two fsts go in, their union comes out. lowkey the whole page is longer than this description, and honestly? slay. 💀

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👑 OPTIONS 👑

first things first, the vibe check on booleans: boolean options are chill like that — you can pass true or false as a value, or you can just say the option name with no value at all and it'll implicitly be true. no cap. ✨

• --fst_align[=BOOLEAN] — write the FST data all aligned where it's appropriate, like a perfectly tidy shelf 🧚 Default: false.
• --fst_compat_symbols[=BOOLEAN] — requires symbol tables to match, when that's the appropriate thing to require. Default: true.
• --fst_default_cache_gc[=BOOLEAN] — turns on garbage collection of the cache. yes, we're cleaning up after ourselves, that's the vibe 🌈 Default: true.
• --fst_default_cache_gc_limit=N — the cache byte size that triggers the garbage collection ✨ Default: 1048576.
• --fst_error_fatal[=BOOLEAN] — if it's true, FST errors are fatal, like actually fatal, do not pass go 💀 if it's not true, then returned objects get flagged as bad instead: FSTs come back with the kError property set to true, and FST weights get set so that Member() returns false. Default: true.
• --fst_field_separator=STRING — sets the characters used as a separator between printed fields. Default: " ".
• --fst_read_mode=STRING — sets the default file reading mode for mappable files, and it's either "read" or "map", no in-betweens 🙈 Default: "read".
• --fst_verify_properties[=BOOLEAN] — verifies the fst properties that TestProperties queries. Default: false.
• --fst_weight_parentheses=STRING — sets the characters that enclose the first weight of a printed composite weight (think pair weight, tuple weight, and derived classes) so nested composite weights do proper I/O, no chaos. it must have size 0 (none) or 2 (open and close parenthesis) — those are the only two moods. Default: no parentheses.
• --fst_weight_separator=CHARACTER — sets the character separator between printed composite weights. Default: comma.
• --help[=BOOLEAN] — show usage information 🫶 Default: false.
• --helpshort[=BOOLEAN] — show the brief usage information. the tldr of the tldr. Default: false.
• --save_relabel_ipairs=FILENAME — save the input relabel pairs to a file. Default: do not save.
• --save_relabel_opairs=FILENAME — save the output relabel pairs to a file. Default: do not save.
• --tmpdir=PATHNAME — sets the temporary directory to use. Default: /tmp.
• --v[=N] — sets the verbosity level. Default: 0.

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🦋 SEE ALSO 🦋

the whole friend group!! go say hi 🫶

• fstarcsort(1), fstclosure(1), fstcompile(1), fstcompose(1), fstcompress(1), fstconcat(1), fstconnect(1), fstconvert(1), fstdeterminize(1), fstdifference(1), fstdisambiguate(1), fstdraw(1), fstencode(1), fstepsnormalize(1), fstequal(1), fstequivalent(1), fstinfo(1), fstintersect(1), fstinvert(1), fstisomorphic(1), fstlinear(1), fstloglinearapply(1), fstmap(1), fstminimize(1), fstprint(1), fstproject(1), fstprune(1), fstpush(1), fstrandgen(1), fstrelabel(1), fstreplace(1), fstreverse(1), fstreweight(1), fstrmepsilon(1), fstshortestdistance(1), fstshortestpath(1), fstsymbols(1), fstsynchronize(1), fsttopsort(1)

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okay that's the whole page, we ate and left absolutely no crumbs 💅 this one's from OpenFst 1.8.5, dated Mar 2026, and that's the tea bestie, stan the manual, mwah 🎀💖✨