如何在Bash 4中将变量每个单词首字母大写、其余字母小写？

Great questions! Bash 4 introduced some really handy parameter expansion tools for case manipulation, so we can handle both your scenarios cleanly. Let’s break them down step by step:

1. Convert Every Word in a Text File/Input Stream #

If you’re working with a text file or piped input, you can use Bash’s built-in case conversion alongside a loop to process each line and word individually:

# Process lines from input.txt and output converted text
while read -r line; do
  converted_line=""
  # Split the line into individual words
  for word in $line; do
    # First convert the entire word to lowercase
    lower_word="${word,,}"
    # Then capitalize the first character
    capitalized_word="${lower_word^}"
    # Build the converted line
    converted_line+="$capitalized_word "
  done
  # Trim the trailing space and print the result
  echo "${converted_line% }"
done < input.txt

If you prefer a more concise one-liner, awk works great here too (and it’s compatible across older Bash versions):

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

2. Convert a Bash Variable’s Words to Title Case #

For a single variable, the approach is similar—split the variable into words, process each one, then reassemble the result:

# Example variable with mixed case formatting
original_var="hELLO wORLD tEST"
converted_var=""

for word in $original_var; do
  # Convert the word to full lowercase, then capitalize the first letter
  processed_word="${word,,}"
  processed_word="${processed_word^}"
  converted_var+="$processed_word "
done

# Remove the trailing space and assign the final result
converted_var="${converted_var% }"
echo "$converted_var"
# Output: Hello World Test

For a shorter variable-focused solution, pipe the variable content to awk:

original_var="hELLO wORLD tEST"
converted_var=$(echo "$original_var" | awk '{for(i=1;i<=NF;i++) $i=toupper(substr($i,1,1)) tolower(substr($i,2)); print}')
echo "$converted_var"

Quick Notes: #

• ${var,,}: A Bash 4+ feature that converts all characters in var to lowercase.
• ${var^}: Another Bash 4+ feature that capitalizes the first character of var.
• By default, Bash splits words using whitespace—if your words include special characters, you may need to adjust the IFS (Internal Field Separator) variable to match your specific use case.

内容的提问来源于stack exchange，提问作者Chris