Bash function body delimiters

bash-functions.sh

#!/usr/bin/env bash

# Bash function bodies can be delimited by curly braces,
# but they don't have to be. The following are all valid
# function body delimiters:
#
#     arithmetic: ((expression))
#     test:       [[ expression ]]
#     subshell:   (list)
#     group:      { list }
#
# Credit for the idea of using non-curly brace delimiters goes to:
# http://stackoverflow.com/questions/27801932/

cat << EOF

###########################################################
# Function using double parentheses (( ... ))
# Used for arithmetic expansion and evaluation
###########################################################

# Print True if number is between 0 and 60, else False
EOF

# Returns true if $1 is an integer between 0 and 60
valid_minutes() ((
    0  <= $1 && \
    $1 <= 60
))

w=59
echo -n "valid_minutes ($w): "
if valid_minutes $w
then
    echo "True"
else
    echo "False"
fi

x=61
echo -n "valid_minutes ($x): "
if valid_minutes $x
then
    echo "True"
else
    echo "False"
fi

# Works the same way as if it was on a single line
y=23
echo -n "single line   ($y): "
if ((0 <= $y && $y <= 60))
then
    echo "True"
else
    echo "False"
fi

# The function itself can be defined on a single line
valid_minutes() ((0 <= $1 && $1 <= 60))

z=-3
echo -n "single line   ($z): "
if valid_minutes $z
then
    echo "True"
else
    echo "False"
fi

cat << EOF

###########################################################
# Function using double square brackets [[ ... ]]
# Used for testing file types and values (Bash-ism)
###########################################################

# Print True if file has rwx permissions, else False
EOF

# Returns true if file has all permissions
is_rwx() [[
    -r $1 && \
    -w $1 && \
    -x $1
]]

temp1=$(mktemp)
chmod u+rwx $temp1

echo -n "rwx------ file: "
if is_rwx $temp1
then
    echo "True"
else
    echo "False"
fi

temp2=$(mktemp)
chmod 500 $temp2

echo -n "r-x------ file: "
if is_rwx $temp2
then
    echo "True"
else
    echo "False"
fi

cat << EOF

###########################################################
# Function using single parentheses ( ... )
# Runs commands in a subshell
###########################################################

# Print first and last element of comma separated list
EOF

# Input argument
list="hello,-7,45,world"
echo "input list: $list"

# IFS (internal field separator) is used to delimit arrays
# Defaults to tab, space, and newline character
echo "IFS before: '$IFS'"

# Returns first and last element of a comma separated list
first_and_last() (
    IFS=','
    array=($1)
    echo ${array[0]} ${array[-1]}
)

echo -n "first_and_last: "
first_and_last $list

# IFS is unchanged since function ran in a subshell
echo "IFS after:  '$IFS'"

cat << EOF

# Find installation directory of Bash
EOF

echo "pwd before: $PWD"

# Returns installation directory of Bash
bash_dir() (
    cd "$(dirname "$(which bash)")"
    pwd
)

echo -n "bash_dir:   "
bash_dir

# PWD is unchanged since function ran in a subshell
echo "pwd after:  $PWD"

cat << EOF

###########################################################
# Function using curly braces { ... }
# Runs commands in a group in the current shell
###########################################################

# Print first and last element of comma separated list
EOF

# Input argument
list="hello,-7,45,world"
echo "input list: $list"

echo "IFS before: '$IFS'"

# Returns first and last element of a comma separated list
first_and_last() {
    IFS=','
    array=($1)
    echo ${array[0]} ${array[-1]}
}

echo -n "first_and_last: "
first_and_last $list

# IFS has changed since function ran in this shell
echo "IFS after:  '$IFS'"

cat << EOF

# Find installation directory of Bash
EOF

echo "pwd before: $PWD"

# Returns installation directory of Bash
bash_dir() {
    cd "$(dirname "$(which bash)")"
    pwd
}

echo -n "bash_dir:   "
bash_dir

# PWD has changed since function ran in this shell
echo "pwd after:  $PWD"