Question

我有一段时间的IFS读取循环来检查行中的不同匹配。

我检查并清空/空行如下：

while IFS= read -r line; do
[[ -z $line ]] && printf some stuff

我还想检查匹配的空/空是否也是文件的最后一行。我将在很多文件上运行这个脚本，它们都是：

- 以空行结尾

- 他们都是不同的长度所以我不能假设任何事情

- 他们有其他空行但不一定在最后（这就是为什么我必须区分）提前谢谢。

Answer 1

正如chepner所指出的，在一个shell读取循环中，知道某一行是否是 last 的唯一方法是尝试读取 next one 。

您可以模仿＆＃34;偷看＆＃34;在下一行使用下面的代码，它允许您在仍然统一处理线条的同时检测所需的条件这个解决方案可能不适合所有人，因为逻辑是非常重要的，因此需要相当多的额外的，非显而易见的代码，并且处理速度也会降低。

请注意，代码假定最后一行有一个尾随\n（因为所有结构良好的多行文本输入都应该有）。

#!/usr/bin/env bash

eof=0 peekedChar= hadEmptyLine=0 lastLine=0
while IFS= read -r line || { eof=1; (( hadEmptyLine )); }; do

  # Construct the 1-2 element array of lines to process in this iteration:
  #   - an empty line detected in the previous iteration by peeking, if applicable
  (( hadEmptyLine )) && aLines=( '' ) || aLines=()
  #   - the line read in this iteration, with the peeked char. prepended
  if (( eof )); then
    # No further line could be read in this iteration; we're here only because
    # $hadEmptyLine was set, which implies that the empty line we're processing
    # is by definition the last one.
    lastLine=1 hadEmptyLine=0
  else  
    # Add the just-read line, with the peeked char. prepended.
    aLines+=( "${peekedChar}${line}" )

    # "Peek" at the next line by reading 1 character, which 
    # we'll have to prepend to the *next* iteration's line, if applicable.
    # Being unable to read tells us that this is the last line.
    IFS= read -n 1 peekedChar || lastLine=1
    # If the next line happens to be empty, our "peeking" has fully consumed it,
    # so we must tell the next iteration to insert processing of this empty line.
    hadEmptyLine=$(( ! lastLine && ${#peekedChar} == 0 ))
  fi

  # Process the 1-2 lines.
  ndx=0 maxNdx=$(( ${#aLines[@]} - 1 ))
  for line in "${aLines[@]}"; do
    if [[ -z $line ]]; then # an empty line
      # Determine if this empty line is the last one overall.
      thisEmptyLineIsLastLine=$(( lastLine && ndx == maxNdx ))
      echo "empty line; last? $thisEmptyLineIsLastLine"
    else
      echo "nonempty line:    [$line]"
    fi
    ((++ndx))
  done

done < file

如何在IFS读取

1 个答案: