About linux : How-to-change-a-specific-character-from-upper-case-to-lower-case-using-awk-or-sed-or-python

I have a line with string of characters (BCCDDDCDCCDDDDDDABCDABCABDBACBDCAACCBBCABACBCCABCACBCDCCCBDBACDCBBCBCBCCCACADAACCABABADBCBAABBBCCBB)

I’d like to replace a specific character (for e.g, 4th character) to lower case.

I have tried with this awk command;

awk '{for (i=1; i<=NF; ++i) { $i=toupper(substr($i,1,1)) tolower(substr($i,2)); } print }' input > output

input file contains the string

"BCCDDDCDCCDDDDDDABCDABCABDBACBDCAACCBBCABACBCCABCACBCDCCCBDBACDCBBCBCBCCCACADAACCABABADBCBAABBBCCBB"

This awk command gives this output:

"Bccdddcdccddddddabcdabcabdbacbdcaaccbbcabacbccabcacbcdcccbdbacdcbbcbcbcccacadaaccababadbcbaabbbccbb"

How do I change all the other characters to lowercase except the 4th character?

On that line you can use something like this. Through -F '' every letter is now a field which can be accessed with $i.

$ cat line
BCCDDDCDCCDDDDDDABCDABCABDBACBDCAACCBBCABACBCCABCACBCDCCCBDBACDCBBCBCBCCCACADAACCABABADBCBAABBBCCBB

$ awk -F '' '{ for(i=1;i<=NF;++i){
    if(i!=4){
      printf("%s",tolower($i))}
    else{
      printf("%s",$i)} } print "" }' line
bccDddcdccddddddabcdabcabdbacbdcaaccbbcabacbccabcacbcdcccbdbacdcbbcbcbcccacadaaccababadbcbaabbbccbb

With GNU sed, would you please try:

sed -E 's/(.{3})(.)/\1\L\2/' YourFile

With python, assuming the variable s is assigned to the line,

print(s[0:3] + s[3:4].lower() + s[4:])

An example in python of a function that makes it, I let you understand the logic and adapt it to your problem.

def f(s):
    # your result
    res = ""

    # iterate though each character in the string
    for i in range(0, len(s)):

        # on some condition, here 4th character, you add a lowercase character to your result
        if(i == 3): 
            res += s[i].lower()

        # on some other conditions an upper case character...
        elif condition_2_to_create: 
            res += s[i].upper()

        # or just the character as it is in the string without modification
        else:
            res += s[i]

    # Then return your result
    return res

Change 4th letter of every line to lowercase:

gawk '{$0 = substr($0,1,3) tolower(substr($0,4,1)) substr($0,5)} 1' YourFile

Or:

gawk -F '' '{$4=tolower($4)} 1' OFS='' YourFile

---

Or with Perl:

perl -pne 'substr($_,4,1) = lc(substr($_,4,1))' YourFile