grep -Po'... \ K ...'有什么作用?还能如何达到这种效果呢? [英] What does grep -Po '...\K...' do? How else can that effect be achieved?

问题描述

我有这个脚本script.sh:

#!/bin/bash
file_path=$1
result=$(grep -Po 'value="\K.*?(?=")' $file_path)
echo $result

和此文件text.txt:

value="a"
value="b"
value="c"

当我运行./script.sh /file/directory/text.txt命令时，终端中的输出如下:

When I run ./script.sh /file/directory/text.txt command, the output in the terminal is the following:

a b c

我了解脚本的功能，但是我不了解它的工作原理，因此我需要对这部分命令进行详细的说明:

I understand what the script does, but I don't understand HOW it works, so I need a detailed explanation of this part of command:

-Po 'value="\K.*?(?=")'

如果我理解正确，那么\K是Perl命令.您能给我一个替代的shell方法吗(例如，使用awk命令)?

If I understood correctly, \K is a Perl command. Can you give me an alternative in shell (for example with awk command)?

谢谢.

推荐答案

• grep -P启用PCRE语法. (这是一个非标准扩展-甚至不是所有的GNU grep构建都支持它，因为它取决于可选的libpcre库，是否将其链接是一个编译时选项).
• grep -o在输出中仅发出匹配的文本，而不发出包含该文本的整行. (尽管它比-P更为广泛，但这也是非标准的.)
• \K是对正则表达式语法的PCRE扩展，它丢弃了该点之前的内容以使其不包含在匹配输出中.
• grep -P enables PCRE syntax. (This is a non-standard extension -- not even all builds of GNU grep support it, as it depends on the optional libpcre library, and whether to link this in is a compile-time option).
• grep -o emits only matched text, and not the entire line containing said text, in output. (This too is nonstandard, though more widely available than -P).
• \K is a PCRE extension to regex syntax discarding content prior to that point from being included in match output.

由于您的外壳是bash，因此您内置了ERE支持.作为一种仅使用内置功能(不使用外部工具，grep，awk或其他方式)的替代方法:

Since your shell is bash, you have ERE support built in. As an alternative that uses only built-in functionality (no external tools, grep, awk or otherwise):

#!/usr/bin/env bash
regex='value="([^"]*)"'                    # store regex (w/ match group) in a variable
results=( )                             # define an empty array to store results
while IFS= read -r line; do             # iterate over lines on input
  if [[ $line =~ $regex ]]; then        # ...and, when one matches the regex...
    results+=( "${BASH_REMATCH[1]}" )   # ...put the group's contents in the array
  fi
done <"$1"                              # with stdin coming from the file named in $1
printf '%s\n' "${results[*]}"           # combine array results with spaces and print

---

请参见 http://wiki.bash-hackers.org/syntax/ccmd/对=~和 http://wiki进行讨论的conditional_expression . bash-hackers.org/syntax/shellvars#bash_rematch 中有关BASH_REMATCH的讨论.有关使用while read逐行读取文件的讨论，请参见 BashFAQ#1 .循环.

---

See http://wiki.bash-hackers.org/syntax/ccmd/conditional_expression for a discussion of =~, and http://wiki.bash-hackers.org/syntax/shellvars#bash_rematch for a discussion of BASH_REMATCH. See BashFAQ #1 for a discussion of reading files line-by-line with a while read loop.

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