String 如何将制表符分隔的数据（始终以字母开头）合并为一个字符串？

我的文件中包含以下数据：

col1 col2 col3 col4 col5 col6  
ABC DEF GE-10 0 0 12 4 16 0  
HIJ KLM 7 0 123 40 0 0  
NOP QL 17 0 0 6 10 1

col1 col2 col3 col4 col5 col6  
ABC DEF GE-10 0 0 12 4 16 0  
HIJ KLM 7 0 123 40 0 0  
NOP QL 17 0 0 6 10 1

我想将所有文本信息合并到一个字符串中（带uu-between），使其如下所示：

col1 col2 col3 col4 col5 col6  
ABC_DEF_GE-10 0 0 12 4 16 0  
HIJ_KLM 7 0 123 40 0 0  
NOP_QL 17 0 0 6 10 1

问题是，某些行的第1-2列和某些行的第1-3列中存在要合并的文本信息

这是如何在Bash中实现的？

test.js

#!/bin/bash.

file='read_file.txt'  
  
#Reading each line  
while read line; do
    #Reading each word  
    wordString=""
    count=1
    for word in $line; do
       if [[ $word =~ ^[0-9]+$ ]];then
            #starts with a numberic value
            wordString="${wordString} ${word}"
            else
            #doesn't starts with a numberic value
            wordString="${wordString}_${word}"
        fi
    done
#remove first character and print the line    
echo ${wordString#?}
done < $file  

test.js

#!/bin/bash.

file='read_file.txt'  
  
#Reading each line  
while read line; do
    #Reading each word  
    wordString=""
    count=1
    for word in $line; do
       if [[ $word =~ ^[0-9]+$ ]];then
            #starts with a numberic value
            wordString="${wordString} ${word}"
            else
            #doesn't starts with a numberic value
            wordString="${wordString}_${word}"
        fi
    done
#remove first character and print the line    
echo ${wordString#?}
done < $file