# Demonstrate 2-tag system can be implemented with `find` and `mkdir` only, # using an example from Wikipedia. # en.wikipedia.org/wiki/Tag_system#Example:_A_simple_2-tag_illustration # _'s are used as a separtor between states. mkdir _ # Production rules for an M-tag system given as constants. M=2 PROD_A="c/c/b/a/H" PROD_B="c/c/a" PROD_C="c/c" # Initial state (surrounded by _'s). mkdir -p _/b/a/a/_ # Alphabets (constant size) S="(/[abcH])" # Keep appending the next state to the end of the state until seeing the halting symbol. e.g. # _/b/a/a/_ -> _/b/a/a/_/a/c/c/a/_ -> _/b/a/a/_/a/c/c/a/_/c/a/c/c/b/a/H/_ -> ... -> .../_/H/c/c/c/c/c/c/a/_ (halt) # # Line 2: Halting condition # Line 3-6: Copy the previous state removing M characters from the start, utilizing back-references. # Line 7-29: Apply the production rule for a, b, c. find _ -regextype posix-extended -empty \( \ -regex ".*_/H.*_|.*_(/[^/]?){,$M}_" -prune -o \ -regex ".*_$S{$M}($S*)/a$S*/_\2" \( -execdir mkdir a/a b/a c/a H/a _/a \; -o -true \) -o \ -regex ".*_$S{$M}($S*)/b$S*/_\2" \( -execdir mkdir a/b b/b c/b H/b _/b \; -o -true \) -o \ -regex ".*_$S{$M}($S*)/c$S*/_\2" \( -execdir mkdir a/c b/c c/c H/c _/c \; -o -true \) -o \ -regex ".*_$S{$M}($S*)/H$S*/_\2" \( -execdir mkdir a/H b/H c/H H/H _/H \; -o -true \) -o \ \( \ -regex ".*_/a$S*/_$S*" \( \ -execdir find a \; -execdir mkdir -p a/$PROD_A/_ \; -o \ -execdir find b \; -execdir mkdir -p b/$PROD_A/_ \; -o \ -execdir find c \; -execdir mkdir -p c/$PROD_A/_ \; -o \ -execdir find H \; -execdir mkdir -p H/$PROD_A/_ \; -o \ -execdir find _ \; -execdir mkdir -p _/$PROD_A/_ \; \ \) -o \ -regex ".*_/b$S*/_$S*" \( \ -execdir find a \; -execdir mkdir -p a/$PROD_B/_ \; -o \ -execdir find b \; -execdir mkdir -p b/$PROD_B/_ \; -o \ -execdir find c \; -execdir mkdir -p c/$PROD_B/_ \; -o \ -execdir find H \; -execdir mkdir -p H/$PROD_B/_ \; -o \ -execdir find _ \; -execdir mkdir -p _/$PROD_B/_ \; \ \) -o \ -regex ".*_/c$S*/_$S*" \( \ -execdir find a \; -execdir mkdir -p a/$PROD_C/_ \; -o \ -execdir find b \; -execdir mkdir -p b/$PROD_C/_ \; -o \ -execdir find c \; -execdir mkdir -p c/$PROD_C/_ \; -o \ -execdir find H \; -execdir mkdir -p H/$PROD_C/_ \; -o \ -execdir find _ \; -execdir mkdir -p _/$PROD_C/_ \; \ \) \ \) \ \) &> /dev/null # Output the result. (_/H/c/c/c/c/c/c/a/_) find _ -depth ! -empty -name _ -execdir find _ -empty \; -quit
Write, Run & Share Bash code online using OneCompiler's Online Bash Shell for free. It's one of the robust, feature-rich Bash shell available over online and getting started with the OneCompiler's Bash Shell is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Bash
. OneCompiler also has reference scripts, where you can look for the sample scripts and start coding.
Bash (Bourne Again Shell) is a shell program written by Brian Fox and is an upgraded version of Bourne Shell program 'sh'.
name="Foo"
echo $name
echo "$name"
echo "${name}"
if [ conditional-expression ]
then
statements
fi
if [ conditional-expression ]
then
statements
else
statements
fi
if [ conditional-expression ]
then
statements
elif [ conditional-expression ]
then
statements
else
statements
fi