Convert array into string

Question

I have a string say, test_var=ab_c_de_fg_.txt. I need to store ab_c in one variable (characters before the 2nd _) and de_fg_ in a second variable (characters after the second _ and before .txt), so these two variables can be used in further operations.

test_var=ab_c_de_fg_.txt for ((i=0;i<{#test_var};i++)) do a[$i]="${var:$i:1}" done flag=0 temp=0 while [["$temp" -le "${#test_var}"]] do if a[temp] -eq "_" && flag -eq 0 flag = 1 continue fi if a[temp] -eq "_" && flag -eq 1 #var1=arr[0] to arr[$(temp-1)] #var2=arr[$(temp+1)] to arr[#(test_var)] fi temp=$((temp+1)) done 

Please guide me, since I am new to shell scripting. Thanks.

Answer 1

To split a string into an array, you can use the split+glob operator (invoked when you leave a parameter expansion unquoted in list context):

test_var=ab_c_de_fg_.txt root_name=${test_var%.*} # remove extension IFS=_ # split on _ set -o noglob # disable glob part array=( $root_name"" ) # split+glob, preserve empty trailing element if any 

typeset -p array would then show something like:

typeset -a array=(ab c de fg '') 

To join elements of an array with the first character (byte in ksh) of $IFS, you do "${array[*]}".

So:

printf '%s\n' "${array[*]:0:2}" "${array[*]:2}" 

Would output:

ab_c de_fg_ 

And your two variables could be defined like:

first_part="${array[*]:0:2}" second_part="${array[*]:2}" 

Answer 2

Here's one way to do what your question asks for in bash (and ignoring your code, since I can't understand what you're trying to do with it):

$ test_var=ab_c_de_fg_.txt $ read var1 var2 < <(echo "$test_var" | sed 's/_/ /2; s/\.txt$//') $ echo "$var1" ab_c $ echo "$var2" de_fg_ 

In a script, that would just be:

test_var=ab_c_de_fg_.txt read var1 var2 < <(echo "$test_var" | sed 's/_/ /2; s/\.txt$//') 

And you now have $var1 and $var2.

The trick is using read to read the two variables. That will split its input on the current value of the environment variable IFS (which, by default, is a space a tab and a newline). The sed command will replace the 2nd _ with a space (s/_/ /2) and remove the .txt from the end of its input (s/\.txt$//), so what is passed to read will be ab_c de_fg_.txt, and because there is a space in the middle, each string is saved in in the corresponding variable.