如何從bash函式呼叫中正確回傳多行字串...？[復制]

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我一直在使用 bash 中的多行字串（無需調出 bash 陣列，這是 POSIX 的東西）。完整的作業演示發布在在線 BASH 仿真器中。

我遇到的問題是，每次我呼叫一個函式并回傳一個字串時，處理多行字串的正確方法會無意中導致在字串末尾附加一個額外的 chr(10)。

建議的重復項不適用：

• 如何從 Bash 函式回傳字串值- 它不能正確處理多行字串變數末尾的空行。
• 我如何在沒有換行符的情況下“回顯”內容？- 它不談論多行非陣列字串變數。

這個多行 bash 字串的作業示例正確地在末尾有一個空行，并且是：

# bash variable declared as multi-line string
ini_buffer="1.1.1.1"
"

將原始多行字串轉換為長度為 8 的十六進制轉儲：

00000000  31 2e 31 2e 31 2e 31 0a  00                       |1.1.1.1..|
00000009

Bash 腳本開始于：

# there is exactly one chr(10) at the end of ini_buffer
ini_buffer="1.2.3.4
"
echo "initial ini_buffer \"\"\"$ini_buffer\"\"\""
echo "initial ini_buffer len: ${#ini_buffer}"
echo


IFS= read -rd '' result < <(echo "$ini_buffer")
# got a SECOND chr(10) prepended to the final output 

echo "result len: ${#result}"
echo "\"\"\"$result\"\"\""
echo

結果是：

initial ini_buffer """1.2.3.4
"""
initial ini_buffer len: 8

result len: 9
"""1.2.3.4

"""

注意到它長出了一個角色？！

00000000  31 2e 31 2e 31 2e 31 0a  0a 00                    |1.1.1.1..|
00000009

添加了第一個功能：

first_function()
{
  local first_buffer result1_buffer
  # takes a string with a single chr(10)
  first_buffer="$1"

  # calls a function, which does nothing.
  IFS= read -rd '' result1_buffer < <(second_function "$first_buffer")
  # yet it got prepended by another chr(10) for a total of two chr(10)

echoerr "result1_buffer len: ${#result1_buffer}"
echoerr "\"\"\"$result1_buffer\"\"\""
  # Suuposedly only one way to return a multi-line string neatly, 
  # and that is via STDOUT (fd=1)
  # echo "first_buffer len: ${#first_buffer}"
  echo "$result1_buffer"
}


# there is exactly one chr(10) at the end of ini_buffer
ini_buffer="1.2.3.4
"
echo "initial ini_buffer \"\"\"$ini_buffer\"\"\""
echo "initial ini_buffer len: ${#ini_buffer}"
echo

#  THIS LINE CHANGED from `echo` to `first_function`
IFS= read -rd '' result < <(first_function "$ini_buffer")
# got a SECOND chr(10) prepended to the final output 
# for a total of 3 prepended chr(10)s

echo "result len: ${#result}"
echo "\"\"\"$result\"\"\""
echo

第一個函式的結果是：

initial ini_buffer """1.2.3.4
"""
initial ini_buffer len: 8

result1_buffer len: 9
"""1.2.3.4

"""
result len: 10
"""1.2.3.4


"""

Every time that a function returning from a nested-called, another chr(10) gets tacked on to it upon return.

This also got increase when a second function was introduced of which I shall not include here for brevity.

This is getting maddening here to me. Has to do with the last-line being blank (or jus a chr(10) character). Not many online authoritative content on proper handling of multi-line string.

What did I do wrong?

Process substitution (<( ... )) gets used here instead of the usual command substitution ($( ... )) which had shown difficulty in working with multi-line string. As a result, I must output any debug stattement to the STDERR using:

echoerr() { printf "%s\n" "$*" >&2; }

I would like to do the proper thing of bash progrmaming with regard to multi-line handling, notably with blank line(s) at the end of its string.

A complete test is reiterated here (working demo link is in cited in the first paragraph):

echoerr() { printf "%s\n" "$*" >&2; }

dump_string_char()
{
  local string len_str idx this_char this_int
  string="$1"
  echoerr "string: \"\"\"$string\"\"\"" 
  len_str="${#string}"
  idx=0
  while [ $idx -lt ${len_str} ]; do
    this_char="${string:$idx:1}"
    this_int="$(LC_CTYPE=C printf "%d" "'$this_char")"
    echoerr "idx: $idx"
    if [ $this_int -lt 32 ]; then
      echoerr "$idx: ${this_int}" 
    else
      echoerr "$idx: \"${this_char}\"" 
    fi
    ((idx  ))
  done
}

second_function()
{
  local second_ini_buffer result2_buffer
  second_ini_buffer="$1"

  # Some magical awk/sed that did not match any pattern
  # So let us use 'echo' to re-save the same string

  IFS= read -rd '' result2_buffer < <(echo "$second_ini_buffer")
  echoerr "result2_buffer len: ${#result2_buffer}"
  echoerr "\"\"\"$result2_buffer\"\"\""
  # so pass back the full ini_buffer as-is.
  # hopefully with ONE chr(1) at end-of-line.
  # but it doesn't.

  echo "$result2_buffer"
}


first_function()
{
  local first_buffer result1_buffer
  # takes a string with a single chr(10)
  first_buffer="$1"

  # calls a function, which does nothing.
  IFS= read -rd '' result1_buffer < <(second_function "$first_buffer")
  # IFS= read -rd '' result1_buffer < <(echo "$first_buffer")
  # yet it got prepended by another chr(10) for a total of two chr(10)

echoerr "result1_buffer len: ${#result1_buffer}"
echoerr "\"\"\"$result1_buffer\"\"\""
  # Suuposedly only one way to return a multi-line string neatly, 
  # and that is via STDOUT (fd=1)
  # echo "first_buffer len: ${#first_buffer}"
  echo "$result1_buffer"
}


# there is exactly one chr(10) at the end of ini_buffer
ini_buffer="1.2.3.4
"
echoerr "initial ini_buffer \"\"\"$ini_buffer\"\"\""
echoerr "initial ini_buffer len: ${#ini_buffer}"
echoerr
dump_string_char "$ini_buffer"


IFS= read -rd '' result < <(first_function "$ini_buffer")
# got a SECOND chr(10) prepended to the final output 
# for a total of 3 prepended chr(10)s

echoerr "result len: ${#result}"
echoerr "\"\"\"$result\"\"\""
echoerr

uj5u.com熱心網友回復：

你的問題是echo總是在你的字串末尾添加一個換行符 - 如果它已經包含一個，它將有兩個。由于您總是“回傳” using echo "$result"，因此每次它都會添加一個新的。

您應該嘗試使用printf "%s" "$result"：

ini_buffer="1.2.3.4
"
echo "initial ini_buffer len: ${#ini_buffer}"

IFS= read -rd '' result < <(printf "%s" "$ini_buffer")

echo "result len: ${#result}"

結果：

initial ini_buffer len: 8
result len: 8

標籤：bash

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