How to use sed command to add a line before a template line?

Question

I want to use sed to modify my file named "baz".

When I search for the template foo, foo is not at the beginning or end of the line, I want to add a panel to foo, how can I do this with sed?

Input file named baz: blah_foo_blahblahblah blah_foo_blahblahblah blah_foo_blahblahblah blah_foo_blahblahblah Output file blah_barfoo_blahblahblah blah_barfoo_blahblahblah blah_barfoo_blahblahblah blah_barfoo_blahblahblah 

Answer 1

You can just use something like:

 sed 's/foo/barfoo/g' baz 

( g at the end means global, each occurrence on each line, not just the first).

For an arbitrary (not fixed) pattern, such as foo[0-9] , you can use capture groups as follows:

 pax$ echo 'xyz fooA abc xyz foo5 abc xyz fooB abc' | sed 's/\(foo[0-9]\)/bar\1/g' xyz fooA abc xyz barfoo5 abc xyz fooB abc 

The brackets capture the actual text that matches the pattern, and \1 uses it as a wildcard.

You can use arbitrarily complex patterns with this, including matching only complete words. For example, only a template change if it is immediately surrounded by a word boundary:

 pax$ echo 'xyz fooA abc xyz foo5 abc foo77 qqq xfoo4 zzz xyz fooB abc' | sed 's/\(\bfoo[0-9]\b\)/bar\1/g' xyz fooA abc xyz barfoo5 abc foo77 qqq xfoo4 zzz xyz fooB abc 

---

In terms of how capture groups work, you can use parentheses to store text that matches the pattern for later use in replacement. Captured identifiers are based on characters ( reading from left to right, so regex (I left the escape characters \ and added it a bit for clarity):

 ( ( \S* ) ( \S* ) ) ^ ^ ^ ^ ^ ^ | | | | | | | +--2--+ +--3--+ | +---------1---------+ 

when applied to Pax Diablo text, you get three groups:

 \1 = Pax Diablo \2 = Pax \3 = Diablo 

as below:

 pax$ echo 'Pax Diablo' | sed 's/\(\(\S*\) \(\S*\)\)/[\1] [\2] [\3]/' [Pax Diablo] [Pax] [Diablo] 

Answer 2

Just replace the beginning of the line with something else.

 sed '/^foo/s/^/bar/' 

Answer 3

To replace or change all "foo" except at the beginning and at the end of the line, I would suggest temporarily replacing them at the beginning and end of the line with a unique breakpoint value.

 sed 's/^foo/____veryunlikelytoken_bol____/ s/foo$/____veryunlikelytoken_eol____/ s/foo/bar&/g s/^____veryunlikelytoken_bol____/foo/ s/____veryunlikelytoken_eol____$/foo/' 

There is no way in sed to indicate "cannot match here." In Perl regular expressions and their derivatives (which means languages ​​that are borrowed from Perl regular expressions, not necessarily languages ​​derived from Perl), you have various negative statements, so you can do something like

 perl -pe 's/(?!^)foo(?!$)/barfoo/g'