AWK \\ SED在单个命令中同时替换字符串的^（开始）和$（end）

Question

I've been looking around but couldn't find a way to do it with both AWK and SED . I was wondering if there's a way to replace a string's start and end in a single command.

more specifically , there's a file with a lot of words in it, and I would like to add something before the word and after the word.

Thanks, Roy

Answer 1

Since you said: more specifically, there's a file with a lot of words in it, and I would like to add something before the word and after the word.

The only thing you need is $& that is match itself. So you simply can write anything that you want just before and end of this whildcard. that's it.

For example say you have this file:

this is line 1.
this is line 2.
this is line 3.

And I tested with perl:
perl -lne 'print "beginning->", $&, "<-end" if /.+/g' file
which the output is:

beginning->this is line 1.<-end
beginning->this is line 2.<-end
beginning->this is line 3.<-end

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May you would like to match only one word, so still this is a good solution such as:

perl -lne 'use English; print "$PREMATCH", "[$MATCH]","$POSTMATCH" if /line/g' file  

Here I matched line and put around that: [ then $& then ]
the output

this is [line] 1.
this is [line] 2.
this is [line] 3.  

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NOTE
As you can see the only things you need just are prematch and match and postmatch . I tested it with perl for you, and if you are interesting in Perl you can use it or may you want to use Sed or Awk . Since you have no specific examples I tested with Perl .

Answer 2

If you want to wrap a particular word with markers you can use & in the replacement string to achieve what you want.

For example to put square brackets around every occurrence of the word bird:

$ echo "hello bird, are you really a bird?" | sed "s/\bbird\b/[&]/g"
hello [bird], are you really a [bird]?

Answer 3

to replace a string's start and end in a single command

Let's say we have a test file with line:

tag hello, world tag

To enclose each tag word with angle brackets < ... > we can apply:

awk approach with gsub() function:

awk '{ gsub(/\<tag\>/, "<&>"); print}' test_file 

word boundaries \\< , \\> may differ depending on awk implementations

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sed approach:

sed 's/\btag\b/<&>/g' test_file 

The output(for both approaches):

<tag> hello, world <tag>