Question

I am attempting to port javascript code to Java. In so doing, I need to replace all of the single quoted strings with double-quoted strings. This also requires me to replace the double-quotes with escaped double-quotes. But I only want to escape the quotes within single-quote string blocks.

I can replace the quoted strings with no problem, using the following sed command:

sed "s/'\([^']*\)'/\"\1\"/g"

This successfully modifies the single-quoted strings to double-quoted strings. But I still have to escape the internal double-quotes. The easiest way would seem to be if sed provided a method by which to run a regex replacement on a section of a line. But I do not know if that is possible.

Answer 1

I don’t think you can do it with sed because its POSIX regex engine doesn’t know lookaround. But it would be possible in (for example) a Python script, by splitting up the operation into two steps:

import re
with open("myfile.js") as infile, open("myfile.jsconv", "w") as outfile:
    for line in infile:
    line = line.sub(
        r"""(?x)"  # Match a double quote
        (?=        # only if it's followed by:
         (?:       # an even number of quotes, defined like this:
          (?:      # Either...
           \\.     # any escaped character
          |        # or
           [^'\\]  # a character except single quotes
          )*       # repeated as needed, followed by
         '         # a single quote.
          (?:\\.|[^'\\])*  # (Repeat this to ensure an even
          '        # number of quotes)
         )*        # Do this zero or more times.
         (?:\\.|[^'\\])* # Then match any remaining characters
         $         # until the end of the line.
        )          # End of loohahead""", 
        '\\"', line)
    line = re.sub(
        r"""(?x)' # Match a single quote
        (         # Match and capture
         (?:      # either...
          \\.     # an escaped character
         |        # or
          [^'\\]  # a character besides quotes or backslashes
         )*       # any number of times.
        )         # End of capturing group number 1
        '         # Match a single quote""", 
        r'"\1"', line)
    outfile.write(line)