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DECREQTPARM / DECREPTPARM — Request and report terminal parameters (`CSI Ps x`)

VT100-era legacy probe — ask the terminal for its serial-line parameters (parity, bit-count, baud, clock multiplier, flags). Predates DA / DA2 / XTVERSION; almost never the right tool now, but xterm and most modern emulators still answer with synthetic defaults.

Byte forms

Every common string-literal form so you can paste-and-search either direction.

\\x1b[\x1b[<Ps>x
\\033[\033[1x
\\e[\e[1x
ESC [ESC [ Ps x
hex1b 5b ... 78

Description

DECREQTPARM — Request Terminal Parameters — CSI Ps x, with Ps selecting solicit-vs-unsolicit convention. Originally wired to the VT100's physical serial line: a host could ask 'what baud / parity / bit-count are you set to?' and the terminal answered with its current setup over the same line.

Request: - Ps = 0 — terminal MAY thereafter send unsolicited DECREPTPARM responses (effectively obsolete; almost no emulator honours this — it's a relic of host-managed setup over a multidrop line). - Ps = 1 — request a solicited response NOW.

Reply (DECREPTPARM) — \x1b[<sol>;<par>;<nbits>;<xspeed>;<rspeed>;<clkmul>;<flags>x - sol = 2 if unsolicited, 3 if solicited (matches your request). - par = parity — 1 = none, 4 = odd, 5 = even. - nbits = data bits — 1 = 8, 2 = 7. - xspeed = transmit speed code (e.g. 16 = 9600, 24 = 38400, 88 = synthetic 'fast' on most emulators). - rspeed = receive speed code (usually equal to xspeed). - clkmul = clock multiplier (always 1 for real VT100; modern emulators echo 1). - flags = STP / SET-UP / TIME bitfield (always 0 on modern emulators).

What modern emulators do: - xterm: full reply with sensible defaults — typically \x1b[3;1;1;112;112;1;0x or \x1b[3;1;1;88;88;1;0x depending on build. The speed code is synthetic and not meaningful. - kitty, wezterm, ghostty, iTerm2, alacritty, Konsole: each implements just enough to not hang a legacy probe — typically returning \x1b[3;1;1;112;112;1;0x or similar. - gnome-terminal: same synthetic shape. - Windows Terminal: replies on builds ≥ 1.18; older builds silent. - macOS Terminal: silent — does not respond. Probes hang until timeout. - cmd.exe / ConPTY: silent. - Linux console (vt): replies with \x1b[3;1;1;112;112;1;0x on most kernels.

Should you actually use this in 2026? Probably never. The reply gives you zero information beyond 'the terminal is alive and speaks ECMA-48', which DA1 (\x1b[c — see csi-da) already answers more cleanly with a model ID. If you find DECREQTPARM in a legacy codebase, it's almost certainly a relic of VT100-era serial-line setup code that never got modernised. Replace with: - csi-da (DA1, \x1b[c) for 'is this a VT-class terminal' / what model. - csi-da2-decoder (DA2, \x1b[>c) for emulator class + firmware version. - xtversion (\x1b[>0q) for specific emulator name + version (xterm-family extension).

If you must use it: send \x1b[1x, read reply on stdin matching \x1b\[3;\d+;\d+;\d+;\d+;\d+;\d+x. Time out at 100 ms — macOS Terminal users will leave you hanging otherwise. Don't treat xspeed/rspeed as a real baud rate; emulators emit constants. The only field that occasionally carries signal is par (parity), and only on serial-attached emulators (gtkterm, picocom — both outside our 12-emulator support row).

Spec citation: DEC VT100 User Guide §4 (DECREQTPARM / DECREPTPARM) / xterm-ctlseqs (CSI Ps x)

Parameters

Ps0 = enable unsolicited DECREPTPARM (almost universally ignored). 1 = request one solicited DECREPTPARM reply now.

Examples

bash
# Solicited probe — read reply non-blocking with 100ms timeout.\nprintf '\\033[1x'\nIFS= read -rs -d x -t 0.1 reply </dev/tty 2>/dev/null\necho \"DECREPTPARM: ${reply#$'\\033'}x\"   # expect \\x1b[3;1;1;<spd>;<spd>;1;0x
python
import sys, re\nsys.stdout.write('\\x1b[1x'); sys.stdout.flush()   # DECREQTPARM solicited\n# ... terminal-aware read of reply (cbreak + select + timeout) ...\n# Match: \\x1b[(\\d+);(\\d+);(\\d+);(\\d+);(\\d+);(\\d+);(\\d+)x\n# Fields: sol par nbits xspeed rspeed clkmul flags
go
// DECREQTPARM — expect \"\\x1b[3;...x\" reply within 100ms or fall back to DA1.\nfmt.Print(\"\\x1b[1x\")
javascript
// Node: probe + parse + fallback.\nprocess.stdout.write('\\x1b[1x');\n// On stdin 'data', match /\\x1b\\[3;(\\d+);(\\d+);(\\d+);(\\d+);(\\d+);(\\d+)x/\n// — fields are mostly synthetic on modern emulators; prefer DA1 + XTVERSION.
c
/* Fire-and-forget DECREQTPARM; most modern emulators answer with constants. */\nprintf(\"\\x1b[1x\"); fflush(stdout);\n/* Parse reply (cbreak terminal): sscanf returned buf,\n *   \"\\x1b[%d;%d;%d;%d;%d;%d;%dx\",\n *   &sol, &par, &nbits, &xspd, &rspd, &clkmul, &flags); */

Terminal support

xterm
yes
Linux console (fbcon)
yes
macOS Terminal.app
no
iTerm2
yes
Windows Terminal
partial
cmd.exe / ConPTY
no
kitty
yes
alacritty
yes
WezTerm
yes
Ghostty
yes
GNOME Terminal
yes
Konsole
yes
tmux
yes
GNU screen
yes

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