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Accepted
Mario Palumbo
Asked: 2020-11-06 06:04:15 +0800 CST

bash --> perl 命令：只打印替换的文本

  • 772

我有文件“test.txt”，其中包含：

Val1 = '59'
Val2 = '76'
Val3 = '42'
Val4 = '53'

我用这个命令：

perl -pe "s/^Val2 = '(.*)'/\1/" test.txt

我想要：

76

但我得到：

Val1 = '59'
76
Val3 = '42'
Val4 = '53'
bash regex perl

2 个回答

  1. Best Answer

    这个-p参数就像 sed 的默认打印 - 也像 sed，如果你想禁止默认打印，你可以使用-n。

    所以你可以做

    perl -ne "print if s/^Val2 = '(.*)'/\1/" test.txt

    您还可以使用正则表达式匹配而不是正则表达式替代：

    perl -lne "print \$1 if /^Val2 = '(.*)'/" test.txt

    或者

    perl -nE "say \$1 if /^Val2 = '(.*)'/" test.txt

    （反斜杠是为了防止$1被 shell 扩展，因为表达式是在双引号中以允许在匹配中使用 Lieral 单引号）。

    • 7

  2. 使用这个 Perl 单行：

    perl -lne "print for /^Val2\s+=\s+'(.*)'/" test.txt

    It is slightly shorter and there is not need to escape any variables, since the for loop passes the captured group (.*) to print implicitly as $_, which is the default argument to print.

    It also uses "\s+" (1 or more whitespace characters) instead of " " (1 blank) to be less strict about the input it accepts. While optional, I prefer to follow the rule about being less strict on the input, and more strict on the output (not sure about the source of this rule, though).

    The Perl one-liner uses these command line flags:
    -e : Tells Perl to look for code in-line, instead of in a file.
    -n : Loop over the input one line at a time, assigning it to $_ by default.
    -l : Strip the input line separator ("\n" on *NIX by default) before executing the code in-line, and append it when printing.

    SEE ALSO:
    perldoc perlrun: how to execute the Perl interpreter: command line switches
    perldoc perlre: Perl regular expressions (regexes)
    perldoc perlre: Perl regular expressions (regexes): Quantifiers; Character Classes and other Special Escapes; Assertions; Capture groups
    perldoc perlrequick: Perl regular expressions quick start

    • 2

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