Bash functions library

2016-10-20

A library of bash functions.

This page lists the bash functions that I needed while developing bash projects.

bash 4.4 was used

How does it work?

Most functions echo something, which is meant as the function's "return". In bash, you can 'capture' what the function outputs.

For instance, to capture the extension of a file, you can use the getFileExtension function like this:

fileExt=$(getFileExtension "fileName.txt")  # store the result of the getFileExtension function in the fileExt variable
echo "$fileExt" # txt

In the function comments, the word 'return' is (mis)used and actually means echo.

Functions index

• endsWith
• getFileExtension
• getValueFromStore
• isMac
• replace
• strlen
• substr

endsWith

# true|false    endsWith ( fileName, expression )
# Returns whether or not the {fileName} ends with the {expression} 
function endsWith {
	if grep -q "$2""$" <<<"$1"; then
		echo 'true'
	else
		echo 'false'
	fi
}

endsWith "fileName.txt" "t" # true
endsWith "fileName.txt" "p" # false
endsWith "fileName.txt" "txt" # true
endsWith "fileName.txt" ".txt" # true
endsWith "fileName.txt" "+txt" # false
endsWith "fileName.txt" "fileName.txt" # true
endsWith "fileName.txt" "ofileName.txt" # false
endsWith "fileName.txt" "TXT" # false

getFileExtension

# emptyString|extension    getFileExtension ( fileName )
# return the extension of the {fileName} string, or an empty string if there is none
function getFileExtension {
	if grep -q '\.' <<<"$1"; then
		echo "${1##*.}"
	else
		echo ""
	fi
}

getFileExtension "fileName.txt" # txt 
getFileExtension "fileName" # (empty string)
getFileExtension "fileName.doo.vm" # vm

getValueFromStore

# string 	getValueFromStore ( key, storePath )
# the store is a file which contains key/value pairs,
# one per line, using the following format:
# key=value
# this function first tries to access the store.
# if the store is not found, the returned value is ERR_STORE_NOT_FOUND
# then, if the key is empty or not found, the returned value is empty string
# if multiple keys are identical, the first one found only will be considered
# The rare case where a line consist only of a matching key (no value, wrong syntax) is not handled, for performance reasons
function getValueFromStore {
	local content
	if [ -f "$2" ]; then
		if [ -n "$1" ]; then
			found="false"
			# http://www.unix.com/shell-programming-and-scripting/161645-read-file-using-while-loop-not-reading-last-line.html
			DONE="false"
			until $DONE; do
			    read line || DONE=true
			    if [ "false" = "$found" ]; then
				    key="$(echo "$line" | cut -d "=" -f 1)"
				    if [ "$1" = "$key" ]; then
				    	echo "$line" | cut -d "=" -f 2
				    	found="true"
				    fi
			    fi
			done < "$2"
		fi
	else
		echo "ERR_STORE_NOT_FOUND"
	fi
}

Examples shown below use a file named store.txt, which contains the following:

key1=value1
key2=This is value 2
key-3="This is value 3"
password1=xaB45

getValueFromStore "ali" "./store.txt" # (empty string)
getValueFromStore "key1" "./store.txt" # value1
getValueFromStore "key1" "./storeddd.txt" # ERR_STORE_NOT_FOUND
getValueFromStore "key2" "./store.txt" # This is value 2
getValueFromStore "key-3" "./store.txt" # "This is value 3"
getValueFromStore "password1" "./store.txt" # xaB45

Note: the getValueFromStore function was originally created to store passwords in a secured centralized place, so that scripts can access it.

isMac

# bool 	isMac (  )
# Whether or not the current machine is a Mac
function isMac {
	if [ -d "/Volumes" ]; then
		echo "true"
	else
		echo "false"
	fi
}


isMac # true (if you are on mac)

replace

# replacedString	replace ( what, byWhat, sourceString )
# note: % symbol are not replaced, unless prefixed with a slash (\%)
function replace {
	echo "${3/$1/$2}"
}

replace "food" "pizza" "I love food" # I love pizza
replace "food" "pizza" "I love cakes" # I love cakes
replace "\%s" "burgers" "I love %s" # I love burgers
replace "%s" "burgers" "I love %s" # I love %burgers
replace "_s_" "burgers" "I love _s_" # I love burgers

strlen

# number    strlen ( string )
# Returns the length of {string}
function strlen {
	echo ${#1} 
}

strlen "fileName.txt" # 12
strlen "fi" # 2
strlen "" # 0

substr

# string	substr ( string, offset )
# string	substr ( string, offset, length )
# Returns the substring of {string} starting from index {offset} (first char is at 0).
# If length is not given, the substring will end at the end of the string
# If length is given, the substring will end when {length} characters are consumed.
# {offset} can be negative.
function substr {
	if [ -n "$3" ]; then
		echo ${1: $2: $3}
	else
		echo ${1: $2}
	fi
}


substr "123456" "0" # 123456
substr "123456" "1" # 23456
substr "123456" "1" "3" # 234
substr "123456" "1" "30" # 23456
substr "123456" "10"  # (empty string)
substr "123456" "-3"  # 456
substr "123456" "-3" "1" # 4