Finding null column value using array

Shell Programming and Scripting
1

hi,
Am trying to find a solution for finding a null column value inside a loop using array.

for eg:

two
three

five

From the above array myarray[0],myarray[3] and myarray[5] having null values. But when am trying to check that space using some condition its not working.
for (( i=0; i<"${#myarray[@]}"; i++ ))
do
space=""
if [[ "${myarray[$i]}" == "$space" ]]    
then
echo "space is there"
else
echo "no space"
fi
done
2

You are aware that there is a huge difference between a space and an empty string, aren't you?

What shell are you using?
What operating system are you using?
Show us how myarray is set.
Show us what output you get when you run your script?

3 
#!/bin/sh
myarray0=( `cat abc` )
space=""
for (( i=0; i<"${#myarray[@]}"; i++ ))
do
space=""
if [[ "${myarray[$i]}" == "$space" ]]
then
echo "space is there"
else
echo "no space"
fi
done

This is my code and below is the file content current shell sh, and Linux OS
cat abc

two
three

five

4

OK. There are two main problems here:

  1. You can't set myarray0 and use myarray in the rest of your code.
  2. And, setting an array using myarray=( `cat filename` ) throws away all of your empty lines.

After that, it isn't clear whether multiple words on a line in your input file should be treated as a single element in your array or as one element for each word. Maybe the following will show you what you did wrong and give you a way to get what you seem to be trying to do:

#!/bin/bash
myarray0=( $(cat abc) )
myarray=( )
myarray2=( )
while read line
do	myarray=( "${myarray[@]}" "$line" )
done < abc
unset line
while read -a line
do	if [ ${#line[@]} -eq 0 ]
	then	myarray2=( "${myarray2[@]}" "" )
	else	myarray2=( "${myarray2[@]}" "${line[@]}" )
	fi
done < abc
space=""
for (( i=0; i<${#myarray0[@]}; i++ ))
do	if [[ "${myarray0[$i]}" == "$space" ]]
	then	echo "myarray0: empty line"
	else	echo "myarray0: data present on line: ${myarray0}"
	fi
done
echo
for (( i=0; i<${#myarray[@]}; i++ ))
do	if [[ "${myarray[$i]}" == "$space" ]]
	then	echo "myarray: empty line"
	else	echo "myarray: data present on line: ${myarray}"
	fi
done
echo
for (( i=0; i<${#myarray2[@]}; i++ ))
do	if [[ "${myarray2[$i]}" == "$space" ]]
	then	echo "myarray2: empty line"
	else	echo "myarray2: data present on line: ${myarray2}"
	fi
done

Note that although this script specifies bash , it also works unchanged with recent version of ksh93 (and with older versions of ksh93 if you change read -a to read -A ).

With the input file abc containing:

one

three

five
six seven eight

it produces the output:

myarray0: data present on line: one
myarray0: data present on line: three
myarray0: data present on line: five
myarray0: data present on line: six
myarray0: data present on line: seven
myarray0: data present on line: eight

myarray: data present on line: one
myarray: empty line
myarray: data present on line: three
myarray: empty line
myarray: data present on line: five
myarray: data present on line: six seven eight

myarray2: data present on line: one
myarray2: empty line
myarray2: data present on line: three
myarray2: empty line
myarray2: data present on line: five
myarray2: data present on line: six
myarray2: data present on line: seven
myarray2: data present on line: eight
5

I'd be surprised if you're running sh as it doesn't provide arrays. Assuming bash , did you consider its mapfile (or readarray ) command?

mapfile myarray <file
IFS= ""
echo "${myarray
[*]}"
one

three

five
six seven eight

---------- Post updated at 11:08 ---------- Previous update was at 10:19 ----------

As for the testing for NULL values in your first post, did you consider the -z test?

for i in "${myarray[@]}"; do [ -z "$i" ] && echo empty || echo $i; done
one
empty
three
empty
five
six seven eight

Use mapfile 's -t option ( mapfile -t <file myarray ) to remove the newline chars from the array.

1 Like