In computer telecommunications, echo is the display or return of sent data at or to the sending end of a transmission. Echo can be either local echo, where the sending device itself displays the sent data, or remote echo, where the receiving device returns th|group=fn}} The echoing is performed by the operating system's terminal device (in some way that is not specified by the POSIX standard). The standard utility program that alters this flag programmatically is the <code><source lang=bash enclose=none>stty</source></code> command, using which th|group=fn}}
- On OpenVMS systems, the operating system's terminal driver normally performs echoing. The terminal characteristic that controls whether it does this is the <code>ECHO</code> characteristic, settable with the DCL command <code>SET TERMINAL /ECHO</code> and unsettable with <code>SET TERMINAL /NOECHO</code>.
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