Modifying Lines in Files In-Place
Parsing files line by line provides a valuable capability for manipulating content. However, if the need arises to edit lines within the file as you traverse them, you may wonder if this is achievable.
Inline Editing
Traditionally, modifying files in-place has not been a straightforward task. However, a simulation technique utilizing backup files, similar to the approach taken by Python's fileinput module, can provide a solution.
Example Script
Consider this example script:
#!/usr/bin/env python import fileinput for line in fileinput.input(inplace=True, backup='.bak'): if some_condition(line): print line, # this goes to the current file
In this script, we read from files provided on the command line or stdin using fileinput.input. By specifying inplace=True, we enable the modification of the current file. The backup parameter creates a backup file with a .bak extension.
Operation
As the script iterates through each line, it evaluates a given condition (some_condition) on each line. If the condition is met, the line is printed back to the current file, effectively modifying it in-place.
Example Usage
For instance, running the script with:
$ python grep_some_condition.py first_file.txt second_file.txt
will result in first_file.txt and second_file.txt containing only lines that satisfy the some_condition() predicate.
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