Bash Golf Part 3

    '\       '\        '\                   .  .          |>18>>
      \        \         \              .         ' .     |
     O>>      O>>       O>>         .                 'o  |
      \       .\. ..    .\. ..   .                        |
      /\    .  /\     .  /\    . .                        |
     / /   .  / /  .'.  / /  .'    .                      |
jgs^^^^^^^`^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        Art by Joan Stark, mod. by Paul Buetow

Table of Contents

• Bash Golf Part 3
• ⇢ FUNCNAME
• ⇢ :(){ :|:& };:
• ⇢ Inner functions
• ⇢ Exporting functions
• ⇢ Dynamic variables with local
• ⇢ if conditionals
• ⇢ Multi-line comments
• ⇢ Don't change it while it's executed

FUNCNAME

#!/usr/bin/env bash

log () {
    local -r level="$1"; shift
    local -r message="$1"; shift
    local -i pid="$$"

    local -r callee=${FUNCNAME[1]}
    local -r stamp=$(date +%Y%m%d-%H%M%S)

    echo "$level|$stamp|$pid|$callee|$message" >&2
}

at_home_friday_evening () {
    log INFO 'One Peperoni Pizza, please'
}

at_home_friday_evening

❯ ./logexample.sh
INFO|20231210-082732|123002|at_home_friday_evening|One Peperoni Pizza, please

:(){ :|:& };:

• :(){ } is really a declaration of the function :
• The ; is ending the current statement
• The : at the end is calling the function :
• :|:& is the function body

• The first : is calling the function recursively
• The |: is piping the output to the function : again (parallel recursion)
• The & lets it run in the background.

Inner functions

#!/usr/bin/env bash

outer() {
  inner() {
    echo 'Intel inside!'
  }
  inner
}

inner
outer
inner

❯ ./inner.sh
/tmp/inner.sh: line 10: inner: command not found
Intel inside!
Intel inside!

#!/usr/bin/env bash

outer1() {
  inner() {
    echo 'Intel inside!'
  }
  inner
}

outer2() {
  inner() {
    echo 'Wintel inside!'
  }
  inner
}

outer1
inner
outer2
inner

❯ ./inner2.sh
Intel inside!
Intel inside!
Wintel inside!
Wintel inside!

Exporting functions

#!/usr/bin/env bash

some_expensive_operations() {
  echo "Doing expensive operations with '$1' from pid $$"
}

for i in {0..9}; do echo $i; done \
  | xargs -P10 -I{} bash -c 'some_expensive_operations "{}"'

❯ ./xargs.sh
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found
bash: line 1: some_expensive_operations: command not found

#!/usr/bin/env bash

some_expensive_operations() {
  echo "Doing expensive operations with '$1' from pid $$"
}
export -f some_expensive_operations

for i in {0..9}; do echo $i; done \
  | xargs -P10 -I{} bash -c 'some_expensive_operations "{}"'

❯ ./xargs.sh
Doing expensive operations with '0' from pid 132831
Doing expensive operations with '1' from pid 132832
Doing expensive operations with '2' from pid 132833
Doing expensive operations with '3' from pid 132834
Doing expensive operations with '4' from pid 132835
Doing expensive operations with '5' from pid 132836
Doing expensive operations with '6' from pid 132837
Doing expensive operations with '7' from pid 132838
Doing expensive operations with '8' from pid 132839
Doing expensive operations with '9' from pid 132840

#!/usr/bin/env bash

some_other_function() {
  echo "$1"
}

some_expensive_operations() {
  some_other_function "Doing expensive operations with '$1' from pid $$"
}
export -f some_expensive_operations

for i in {0..9}; do echo $i; done \
  | xargs -P10 -I{} bash -c 'some_expensive_operations "{}"'

Dynamic variables with local

#!/usr/bin/env bash

foo() {
  local foo=bar # Declare local/dynamic variable
  bar
  echo "$foo"
}

bar() {
  echo "$foo"
  foo=baz
}

foo=foo # Declare global variable
foo # Call function foo
echo "$foo"

❯ ./dynamic.sh
bar
baz
foo

if conditionals

#!/usr/bin/env bash

declare -r foo=foo
declare -r bar=bar

if [ "$foo" = foo ]; then
  if [ "$bar" = bar ]; then
    echo ok1
  fi
fi

if [ "$foo" = foo ] && [ "$bar" == bar ]; then
  echo ok2a
fi

[ "$foo" = foo ] && [ "$bar" == bar ] && echo ok2b

if [[ "$foo" = foo && "$bar" == bar ]]; then
  echo ok3a
fi

 [[ "$foo" = foo && "$bar" == bar ]] && echo ok3b

if test "$foo" = foo && test "$bar" = bar; then
  echo ok4a
fi

test "$foo" = foo && test "$bar" = bar && echo ok4b

❯ ./if.sh
ok1
ok2a
ok2b
ok3a
ok3b
ok4a
ok4b

Multi-line comments

#!/usr/bin/env bash

# Single line comment

# These are two single line
# comments one after another

: <<COMMENT
This is another way a
multi line comment
could be written!
COMMENT

Don't change it while it's executed

#!/usr/bin/env bash

echo foo
echo echo baz >> $0
echo bar

❯ ./if.sh
foo
bar
baz
❯ cat if.sh
#!/usr/bin/env bash

echo foo
echo echo baz >> $0
echo bar
echo baz

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