[Linuxcommand-announce] [LinuxCommand.org: Tips, News And Rants] tput

[William S. <bs...@pa...>]

In a recent post, we covered a technique that can produce colored text
on the command line. Today, we will look at a more general approach to
producing not only text effects, but also gaining more visual control
of our terminal.

A Little History

Back in the old days, when computers were connected to remote
terminals, many brands of terminals existed and they were all a little
different in terms of their feature sets and capabilities. As a result,
different terminals used different sets of commands to control them.

Terminals responds to codes (called control codes) embedded in the
stream of text sent to them. Some of these codes are standard and
familiar like carriage return and line feed. Others, like those to turn
on bold text or underlining are not. Terminals can, in fact, perform
many kinds of functions. As microprocessors became available and the
advent of the personal computer loomed, terminals became
increasingly "smart" and feature laden.

However the proliferation of terminal brands and feature sets posed a
problem for software developers. Software had to be painstakingly
customized to support a particular terminal. What was needed was a
software system that supported hardware independence so that
applications could use a standard set of commands to deal with any
terminal. This problem was addressed in two ways. First a standard set
of control sequences were developed by ANSI (American National
Standards Institute) and adopted (in varying degrees) by terminal
manufactures to give all terminals a common set of commands. We looked
at the ANSI commands in a an earlier post. The second approach was
development of an intermediary layer (much like today's notion of a
device driver) that translates a standardized command into the specific
control codes used by a particular terminal.

In the Unix world, there are two such systems, the original, termcap
and the more recent terminfo. Both contain a database of control code
sequences used by different kinds of terminals.

Enter tput

tput is a command that can query the terminfo database to see if a
particular terminal can support a particular feature. It can also
accept terminal commands and output (via standard output) the control
code sequences for that terminal. tput is generally used like this:

tput capname [parameters...]

where capname is the name of a terminal capability and parameters are
any option parameters associated with the specified capability. For
example, to output the sequence of instructions needed to move the
cursor to the upper left corner of the screen (the "home" position):

tput cup 0 0

which means cursor position row 0, column 0.

Since tput actually outputs the sequence to standard output (you won't
see the sequence since it is interpreted by your terminal emulator as
an instruction), you can store the sequences in variables. Here we will
store the sequences to control bold text:

bold_on=$(tput bold)
bold_off=$(tput sgr0)

Now, to highlight some text, you could:

echo "This is ${bold_on}important${bold_off}."

and you get this:

This is important.

There are a huge number of terminal capabilities, though most terminals
only support a small subset. Besides changing text colors and
positioning the cursor, it is possible to erase text, insert text, and
control text attributes. The terminfo man page lists all the terminal
capabilities and the Bash Prompt HOWTO section 6.5 (see "Further
Reading" below) describes the ones most useful for ordinary screen
control.

Before we leave, here is a version of the prompt_colors script that
uses tput to set foreground and background text colors:

#!/bin/bash

# prompt_colors -- demonstrate prompt color combinations.

for fore in {0..7}; do
set_foreground=$(tput setf $fore)
for back in {0..7}; do
set_background=$(tput setb $back)
echo -n $set_background$set_foreground
printf ' F:%s B:%s ' $fore $back
done
echo $(tput sgr0)
done

Further Reading

- tput man page

- terminfo man page

- http://en.wikipedia.org/wiki/Computer_terminals

- http://en.wikipedia.org/wiki/Terminfo

- http://en.wikipedia.org/wiki/Tput

- http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x405.html

- http://tldp.org/HOWTO/Text-Terminal-HOWTO.html


--
Posted By William Shotts to LinuxCommand.org: Tips, News And Rants at
2/17/2010 05:38:00 PM