sorted by: recent | see : popular

Content Tagged with utility + linux

Since the very early days, the MySQL distribution packages contain a very useful commandline-tool named replace. As the name implies, it can be used to replace strings in text files. From the documentation:

The replace utility program changes strings in place in files or on the standard input. Invoke replace in one of the following ways:

shell> replace from to [from to] ... -- file [file] ...
shell> replace from to [from to] ... < file

from represents a string to look for and to represents its replacement. There can be one or more pairs of strings. Use the -- option to indicate where the string-replacement list ends and the filenames begin. In this case, any file named on the command line is modified in place, so you may want to make a copy of the original before converting it. replace prints a message indicating which of the input files it actually modifies. If the -- option is not given, replace reads the standard input and writes to the standard output. replace uses a finite state machine to match longer strings first. It can be used to swap strings. For example, the following command swaps a and b in the given files, file1 and file2:

shell> replace a b b a -- file1 file2 ...

This comes in very handy, especially if you need to replace a similar text in a large number of files, or if you need to replace multiple different strings in a file at the same time! So next time you need to replace strings in text files, take a look at this hidden gem!

Unfortunately the string matching does not support regular expressions - but the source code actually documents some additional options:

Special characters in from string:
  ^  Match start of line.
  \$  Match end of line.
  \b  Match space-character, start of line or end of line.
        For end \b the next replace starts locking at the end space-character.
        An \b alone or in a string matches only a space-character.
  \r, \t, \v as in C.

The programs make a DFA-state-machine of the strings and the speed isn't
dependent on the count of replace-strings (only of the number of replaces).
A line is assumed ending with \n or \0.
There are no limit exept memory on length of strings.