```{index} single: tcflow; POSIX function ``` ```{index} single: POSIX::tcflow; Perl function ``` # tcflow Suspend or resume transmission or reception on terminal `$fd`. ## Synopsis ```perl use POSIX qw(tcflow TCOOFF TCOON); tcflow($fd, TCOOFF); # pause output ``` ## What you get back `"0 but true"` on success, `undef` on failure. Negative `$action` sets `$!` to `EINVAL`. ## Differences from upstream Fully compatible with upstream POSIX.