In this example, the `re.sub()` function searches for one or more digits in the original string and replaces them with the string “NUM”. This is a sample text with NUM numbers in it. New_string = re.sub(pattern, replacement_string, original_string) # replace the pattern with the replacement string # define the string to replace the pattern with Pattern = r'd+' # d matches digits, + means one or more occurrences # define the pattern to search for (in this case, digits) Original_string = "This is a sample text with 123 numbers in it." This function takes three main arguments: the pattern to search for, the string to replace it with, and the original string. To replace a string using regex, you can use the `re.sub()` function. You can use the `re` module in Python to work with regular expressions. We’ll also provide an example so you can see it in action.
#Python regex replace how to#
In this blog post, we’ll look at how to use the `re.sub()` function to do just that – replacing a string based on a pattern defined by regular expression syntax. Perl also allows changing the files in place, with the addition of the ‘-i’ flag, usually used as ‘-i.bak’ to make backup copies of the original: perl -pi.bak -e 's/foo/bar/g ' example.Are you looking for an easy way to work with regular expressions in Python? The `re` module provides a powerful set of tools that can help you search and replace strings using regex. The following scripts are equivalent: #!/usr/bin/perl cat example.txt | perl -e 'while ()Īnd of course, you don’t have to use the ‘-e’ flag.cat example.txt | perl -ne 's/foo/bar/g print'.cat example.txt | perl -pe 's/foo/bar/g '.The following are all roughly equivalent: There are lots of ways to implement this in Perl. Therefore, I’m presenting Perl versions that I’ve used before, mostly as a comparison. Here, I’m looking for things that look like * (#the_anchor)Īs I’ve mentioned before, I still use Perl sometimes, even though I like to use Python for most of my scripting needs.
#Python regex replace series#
Of course, foo and bar don’t have to be so simple.įor example, the markdown issue I have with converting a table of contents to a series of h2 tags, can be solved with the following script. If you leave the ‘backup’ flag out, no backup will be made.Īs I’ve shown it with backup='.bak', an file will be created. import fileinputįor line in fileinput.input(inplace=1, backup='.bak'): In place modification of files #Ī slightly modified script will allow you to modify files, and optionally copy the original file to a backup. This handles the case where we don’t want to modify the file. The ‘rstrip’ is called on the input just to strip the line of it’s newline, since the next ‘print’ statement is going to add a newline by default. The re (regex, regular expression) module has sub which handles the search/replace. The fileinput module takes care of the stream verses filename input handling. Line = re.sub('foo','bar', line.rstrip()) I think the most basic form of a search/replace script in python is something like this: import fileinput using Python # Search and replace as a filter #
We can all of those things, as I’ll show below. I also may want to make a backup of example.txt first. If not, then the second example above would just print the modified contents. Now, I may or may not want to have the script modify the file in place. cat example.txt | python search_replace.py.I’d like to be able to have a script that runs in a way that I can either pipe the contents of the file into the script, or just give a file name to the script, like this: I realize that I want to replace ‘foo’ with ‘bar’. The dummy situation I’m going to set up is this. However ‘foo’ can be ANY regular expression. In most of the following discussion, I’m just replacing ‘foo’ with ‘bar’. I’ll also show similar Perl versions, mainly for comparisons. I’ve put together my standard methods for tackling the problem. There are probably endless solutions to the problem. Search and replace is such a common task that it should be a tool that’s in every command line script author’s toolbox.
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