The Linux Programming Interface

1296 Chapter 62

62.4 Terminal Special Characters

Table 62-1 lists the special characters recognized by the Linux terminal driver. The

first two columns show the name of the character and the corresponding constant

that can be used as a subscript in the c_cc array. (As can be seen, these constants

simply prefix the letter V in front of the character name.) The CR and NL charac-

ters don’t have corresponding c_cc subscripts, because the values of these characters

can’t be changed.

The Default setting column of the table shows the usual default value for the

special character. As well as being able to set a terminal special character to a spe-

cific value, it is also possible to disable the character by setting it to the value

returned by the call fpathconf(fd, _PC_VDISABLE), where fd is a file descriptor refer-

ring to a terminal. (On most UNIX implementations, this call returns the value 0.)

The operation of each of the special characters is subject to the setting of vari-

ous flags in the termios bit-mask fields (described in Section 62.5), as shown in the

penultimate column of the table.

The final column indicates which of these characters are specified by SUSv3.

Regardless of the SUSv3 specification, most of these characters are supported on

all UNIX implementations.

The following paragraphs provide more detailed explanations of the terminal spe-

cial characters. Note that if the terminal driver performs its special input interpre-

tation on one of these characters, then—with the exception of CR, EOL, EOL2, and

NL—the character is discarded (i.e., it is not passed to any reading process).

Table 62-1: Terminal special characters

Character c_cc

subscript

Description Default

setting

Relevant

bit-mask flags

SUSv3

CR (none) Carriage return ^M ICANON, IGNCR, ICRNL,

OPOST, OCRNL, ONOCR

DISCARD VDISCARD Discard output ^O (not implemented)

EOF VEOF End-of-file ^D ICANON •

EOL VEOL End-of-line ICANON •

EOL2 VEOL2 Alternate end-of-line ICANON, IEXTEN

ERASE VERASE Erase character ^? ICANON •

INTR VINTR Interrupt (SIGINT) ^C ISIG •

KILL VKILL Erase line ^U ICANON •

LNEXT VLNEXT Literal next ^V ICANON, IEXTEN

NL (none) Newline ^J ICANON, INLCR, ECHONL,

OPOST, ONLCR, ONLRET

QUIT VQUIT Quit (SIGQUIT) ^\ ISIG •

REPRINT VREPRINT Reprint input line ^R ICANON, IEXTEN, ECHO

START VSTART Start output ^Q IXON, IXOFF •

STOP VSTOP Stop output ^S IXON, IXOFF •

SUSP VSUSP Suspend (SIGTSTP) ^Z ISIG •

WERASE VWERASE Erase word ^W ICANON, IEXTEN