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Sunday, April 18, 2010

How to Handle Cursor Movement in a Shell Script


Using ANSI escape sequences :


ANSI escape sequences or tput allow you to move the cursor around the
screen at will. This is more useful for full screen user interfaces
generated by shell scripts, but can also be used in prompts.

The movement escape sequences are as follows:

- Position the Cursor:
\033[<L>;<C>H
Or
\033[<L>;<C>f
puts the cursor at line L and column C.
- Move the cursor up N lines:
\033[<N>A
- Move the cursor down N lines:
\033[<N>B
- Move the cursor forward N columns:
\033[<N>C
- Move the cursor backward N columns:
\033[<N>D
- Clear the screen, move to (0,0):
\033[2J
- Erase to end of line:
\033[K
- Save cursor position:
\033[s
- Restore cursor position:
\033[u

The latter two codes are NOT honored by many terminal emulators. The
only ones that I'm aware of that do are xterm and nxterm - even though
the majority of terminal emulators are based on xterm code. As far as
I can tell, rxvt, kvt, xiterm, and Eterm do not support them. They are
supported on the console.

$ echo -en "\033[s\033[7B\033[1;34m BASH BASH\033[u\033[0m"

Above line saves the current cursor position(\033[s), then move the
cursor seven lines down the screen(\033[7B),print the word "BASH BASH"
in dark blue color(\033[1;34m), and then return to where it started to
produce a normal prompt(\033[u), and also back to the normal color
(\033[0m).

Example:

$ echo -en "\033[s\033[7B\033[1;34m BASH BASH\033[u\033[0m"
$






BASH BASH

Using tput command:


As with so many things in Unix, there is more than one way to achieve
the same ends.A utility called tput can also be used to move the cursor
around the screen, get back information about the status of the termi-
nal, or set colors.

man tput doesn't go into much detail about the available commands,but
man terminfo will give you a huge list of capabilities, many of which
are device independent, and therefore better than the escape sequences
previously mentioned.

Here is some useful tput capabilities:

tput Cursor Movement Capabilities:

tput cup Y X
Move cursor to screen location X,Y (top left is 0,0)

tput sc
Save the cursor position

tput rc
Restore the cursor position

tput lines
Output the number of lines of the terminal

tput cols
Output the number of columns of the terminal

tput cub N
Move N characters left

tput cuf N
Move N characters right
tput cuu N
up N lines

tput cud N
down N lines

tput Colour Capabilities :

tput setab [1-7]
Set a background colour using ANSI escape

tput setb [1-7]
Set a background colour

tput setaf [1-7]
Set a foreground colour using ANSI escape

tput setf [1-7]
Set a foreground colour

tput Text Mode Capabilities:

tput bold
Set bold mode

tput dim
turn on half-bright mode

tput smul
begin underline mode

tput rmul
exit underline mode

tput rev
Turn on reverse mode

tput smso
Enter standout mode (bold on rxvt)

tput rmso
Exit standout mode

tput sgr0
Turn off all attributes (doesn't work quite as expected).

tput Clear and Insert Capabilities :

tput ech N
Erase N characters

tput clear
clear screen and home cursor

tput el1
Clear to beginning of line

tput el
clear to end of line

tput ed
clear to end of screen

tput ich N
insert N characters (moves rest of line forward!)

tput il N
insert N lines

This is by no means a complete list of what terminfo and tput allow,
in fact it's only the beginning. man tput and man terminfo if you want
to know more.

Example:

$ tput sc;tput cup 4 35;tput setaf 2;echo "Hello World";\
> tput rc;tput sgr0
$

Hello World


Bellow example shows two different ways to achieve same task:

$ tput sc;tput cud 7;tput setaf 4;echo BASH BASH; tput rc;\
> tput sgr0
$ echo -en "\033[s\033[7B\033[0;34m BASH BASH\033[u\033[0m"

6 comments:

  1. How could you move to column 35 on the current line with tput witout having to specify the line to be on?

    ReplyDelete
  2. Thank You for helping a beginner.

    ReplyDelete
  3. Very nicely done, I appreciate it.

    ReplyDelete
  4. Charles,
    MyColumns=`tput cols`
    tput cub $MyColumns; tput cuf 35

    ReplyDelete
  5. Thank you so much!

    ReplyDelete