file-io - 用 Common Lisp 就地替换文件中的正则表达式

Question

我正在尝试编写 Python 正则表达式搜索和替换的 Common Lisp 版本，并对文件进行就地修改:

import fileinput, re

for line in fileinput.input(inplace=1, backup='.bak'):
    line = re.sub(r"foo", "bar", line, re.M)
print (line)

这是我能想到的 Common Lisp 代码:

(require :cl-ppcre)

(defun in-place-subst (file)
  (with-open-file (stream file :direction :io :if-exists :overwrite)
    (loop for line = (read-line stream nil)
       while line do
         (write-line (cl-ppcre:regex-replace-all "foo" line "bar") stream))))

有点儿管用。现在，替换文本将附加在文件末尾。我的直接问题是我不知道如何替换内容。

为了更好地解释，如果 file.txt 包含:

1 foo
2 bar
3 foobar

调用后

(in-place-subst "file.txt")

我得到:

1 foo
2 bar
3 foobar
1 bar
2 bar
3 barbar

而不是正确的替换:

1 bar
2 bar
3 barbar

我尝试了所有可能的 with-open-file 选项(来自 Successful Lisp )，但没有成功:

Keyword      Value                Action if File Exists
----------   ------------------   ---------------------------------------
:IF-EXISTS   NIL                  return NIL
:IF-EXISTS   :ERROR               signal an error
:IF-EXISTS   :NEW-VERSION         next version (or error)
:IF-EXISTS   :RENAME              rename existing, create new
:IF-EXISTS   :SUPERSEDE           replace file upon CLOSE
:IF-EXISTS   :RENAME-AND-DELETE   rename and delete existing, create new
:IF-EXISTS   :OVERWRITE           reuse existing file (position at start)
:IF-EXISTS   :APPEND              reuse existing file (position at end)

有人能告诉我正确的方向，以便该函数以正确的方式呈现 file.txt 吗？

此外，假设 cl-ppcre 可用，Common Lisp 的惯用 方法是什么？

是否有更简洁的方法来使用 Common Lisp 进行就地正则表达式替换？

Answer 1

在 Python 中，没有“就地”修改文件的原始操作；反而，有一个辅助类 fileinput 的函数，它给人一种错觉通过首先将文件复制到备份文件来就地修改文件，然后读取备份文件并将处理结果写入原始文件。来自manual :

Optional in-place filtering: if the keyword argument inplace=1 is passed to fileinput.input() or to the FileInput constructor, the file is moved to a backup file and standard output is directed to the input file (if a file of the same name as the backup file already exists, it will be replaced silently). This makes it possible to write a filter that rewrites its input file in place. If the backup parameter is given (typically as backup='.'), it specifies the extension for the backup file, and the backup file remains around; by default, the extension is '.bak' and it is deleted when the output file is closed. In-place filtering is disabled when standard input is read.

因此，在 Common Lisp 中执行此操作的方式是模仿 Python code ，首先将文件复制到备份文件，例如使用此 function my-copy-file，然后编写如下代码:

(defun in-place-subst (file)
  (let ((backup-file (concatenate 'string file ".bak")))
    (my-copy-file file backup-file)
    (with-open-file (in-stream backup-file)
      (with-open-file (out-stream file :direction :output :if-exists :supersede)
        (loop for line = (read-line in-stream nil)
           while line do
             (write-line (cl-ppcre:regex-replace-all "foo" line "bar") out-stream))))))