Replace one regex, then replace second regex in all lines not matching first

Question

Example task: if a line contains foo, replace it with bar, otherwise append baz to the line.

sed -e s/foo/bar/ -e s/$/baz/ doesn't work, as the second command gets executed whether or not the first one matches. Is there a way to tell sed to go to the next line after a match?

Answer 1

You can use the t command without a label to start next cycle on successful substitution

$ cat ip.txt 
a foo 123
xyz
fore
1foo

$ sed -e 's/foo/bar/' -e t -e 's/$/baz/' ip.txt
a bar 123
xyzbaz
forebaz
1bar

From manual:

t label (test)

Branch to label only if there has been a successful substitution since the last input line was read or conditional branch was taken. The label may be omitted, in which case the next cycle is started.

Answer 2

A more robust way with awk script:

awk '{ if (/foo/) gsub(/foo/, "bar"); else $0 = $0 "baz" }1' file

---

Or even shorter:

awk '{ if (!gsub(/foo/, "bar")) $0 = $0 "baz"; }1' file

Answer 3

Try this:

sed -e '/foo/!s/$/baz/g' -e s/foo/bar/g

Answer 4

Figured it out:

sed -e '/foo/{s//bar/;p;D};s/$/baz/' 

Explanation:

• Multiple sed commands can be chained with ; and grouped with { ... }.
• /foo/ selects all lines containing the pattern foo.
• s//bar/ is the same as s/foo/bar/ - an empty pattern means to repeat the last search (in this case, foo).
• p means to print the pattern space (the line after the substitution).
• D means to clear the current line, and go to the next one.
• s/$/baz/ will perform the second part of the task, i.e. append baz to lines which the previous rule left to pass through.