Perl命令行上的多个正则表达式无法按预期工作

Question

I am using two regexp expressions in a perl command-line, but it doesn't give the expected result:

$ cat test
foo
bar
#baz
#haz
naz
$ perl -pe 's/\n/\\n/g; s/\\n#.*$/CHEESE/' test
foo\nbar\n#baz\n#haz\nnaz\n\n

I would expect the result to be foo\\nbarCHEESE . What am I doing wrong?

Answer 1

The problem is that your input file is being read one line at a time; the code is executed once for each line of input. Because the newline character is at the end of each line, the second regex pattern \\\\n#.*$ can never match

The solution is to enable slurp mode which fetches the whole file in a single read. Then your subsitutions will happen only once. A switch value of -0777 will do this for you

$ perl -0777 -pe 's/\n/\\n/g; s/\\n#.*$/CHEESE/' test

output

foo\nbarCHEESE