How to convert from row to column?

Pretty easy with tr:

tr -s '[:blank:]' '\n' <file.txt

Example:

% cat file.txt                    
106849_01373    106849_01967    106850_00082    23025.7_01059   
106849_01373    106849_01967    106850_00082    23025.7_01059   
106849_01373    106849_01967    106850_00082    23025.7_01059   
106849_01373    106849_01967    106850_00082    23025.7_01059   

% tr -s '[:blank:]' '\n' <file.txt
106849_01373
106849_01967
106850_00082
23025.7_01059
106849_01373
106849_01967
106850_00082
23025.7_01059
106849_01373
106849_01967
106850_00082
23025.7_01059
106849_01373
106849_01967
106850_00082
23025.7_01059

Here is one with xargs

xargs -n1 < file.txt

Demo:

$ cat file.txt                    
106849_01373    106849_01967    106850_00082    23025.7_01059 

$ xargs -n1 < file.txt
106849_01373
106849_01967
106850_00082
23025.7_01059

heemayl's answer is the way to go, however here's an alternative using Perl:

perl -lane '$,="\n"; print(@F)' file.txt

• -l: enables automatic line-ending processing. It has two separate effects. First, it automatically chomps $/ (the input record separator) when used with -n or -p. Second, it assigns $\ (the output record separator) to have the value of octnum so that any print statements will have that separator added back on. If octnum is omitted, sets $\ to the current value of $/.
• -a: turns on autosplit mode when used with a -n or -p. An implicit split command to the @F array is done as the first thing inside the implicit while loop produced by the -n or -p.

• -n: causes Perl to assume the following loop around your program, which makes it iterate over filename arguments somewhat like sed -n or awk:

  LINE:
    while (<>) {
        ...             # your program goes here
    }
  

• -e: may be used to enter one line of program;

• $,="\n": sets the output field separator to a newline;
• print(@F): prints the fields separated by the output field separator.

% cat file.txt
106849_01373    106849_01967    106850_00082    23025.7_01059 
% perl -lane '$,="\n"; print(@F)' file.txt
106849_01373
106849_01967
106850_00082
23025.7_01059