BASH on fire
A question that worries shell programmers for ages was answered! How to make some classic demo effect like fire in Bourne again shell? :-) See the answer below.
Updated version (2012-JAN-17)
I was playing with the code, to made some updates. First of all, I test size of terminal with tput command. Also there are few minor changes to clean up the code, so I saved almost 100 bytes! I've tried to improve the speed, but any change is not noticeable :(
The fire effect is computed inside one big string (columns × rows) and
the numbers inside the string addressing pixel palette
B=(' ' '\E[0;31m.' '\E[0;31m:' '\E[1;31m+' '\E[0;33m+' '\E[1;33mU' '\E[1;33mW');
echo -e ${B[*]}
Each „pixel“ contains ANSI code for terminal color and some character to create the fading effect.
The nice description of fire algorithm can be find here.
#!/bin/bash X=`tput cols` Y=`tput lines` e=echo M=`eval $e {1..$[X*Y]}` P=`eval $e {1..$X}`; B=(' ' '\E[0;31m.' '\E[0;31m:' '\E[1;31m+' '\E[0;33m+' '\E[1;33mU' '\E[1;33mW'); $e -e "\E[2J\E[?25l" ; while true; do p=''; for j in $P; do p=$p$[$RANDOM%2*9]; done;O=${C:0:$[X*(Y-1)]}$p;C='' S='';for p in $M;do # _-=[ BruXy.RegNet.CZ ]=-_ read a b c d <<< "${O:$[p+X-1]:1} ${O:$[p+X]:1} ${O:$[p+X+1]:1} ${O:$[p+X+X]:1}" v=$[(a+b+c+d)/4] C=$C$v S=$S${B[$v]}; done; printf "\E[1;1f$S"; done # (c) 2012
Old version
Copy and save the following code, make it executable using chmod +x fire.sh and run it with parametr ./fire.sh $COLUMNS. This variable contains number of columns in current terminal window. I recommend to change the window size to see the effect in better speed.
#!/bin/bash
e=echo\ -e X=$1 Y=$[(X*5)/16] M=`eval $e {1..$[X*Y]}` #######
P=`eval $e {1..$X}}`;for i in $M; do S=$S"0";done;u=0; ######
B=(" " "\E[0;31m." "\E[0;31m:" "\E[1;31m+" "\E[0;33m+" #####
"\E[1;33mU" "\E[1;33mW");$e "\E[2J\E[?25l";while true;do ####
p='';for j in $P;do p=$p$[$RANDOM%2*9];done; [ $u -gt 0 ] \
&&O=${C:0:$[X*(Y-1)]}$p; [ $[u++] -eq 0 ] && O=$S$p;C='' ####
S=''; for p in $M; do a=${O:$[p+X-1]:1} b=${O:$[p+X]:1} #####
c=${O:$[p+X+1]:1} d=${O:$[p+X+X]:1} v=$[ (a+b+c+d)/4] ######
C=$C$v S=$S${B[$v]}; done; $e "\E[1;1f";$e "$S";done #BruXy#