You want to match:. You can do that by putting the string "," in a group, enclosing it in parentheses. But parentheses do even more. They store what they match, which is called capturing it. Then you can refer to it later. This is a subtle and possibly confusing feature. Let's show it by looking at a file that repeats some sequences of characters:.
The first line contains the word "tam", a hyphen, and then "tam" again. The third line contains "quick", a hyphen, and then "quick" again.
These lines don't actually have strings in common, except for the hyphen which appears in the second line too, so searching for it doesn't distinguish the first and third lines from the second. What the first and third lines share is a pattern: a word followed by a hyphen and itself.
So we can grab those two lines by capturing a word and repeating it the file is named doubles :. The is a special syntax recognized by tools that allow parentheses to capture text. It says, "whatever you found, I want it again. To extract the second part of an email address, such as "fsf. In this case, matches the part before the sign, while matches the part after the. So extract to get "fsf. We saw that a character class matches only one character at a time.
If you have two or more sequences that can appear in the same place, you specify them through alternation. This involves separating them with a vertical bar. Because the alternatives are usually embedded in a larger regular expression, you generally need to put them in parentheses to mark where they start and end:. Thus, you can use the following to catch lines that begin with a lowercase letter:. This use of the caret has nothing to do with the caret that we saw before inside of square brackets.
A caret means "beginning of line" when it's the first character of a regular expression, but only in that position. In the phrase "I added 3 and 5 to make 8", the previous regular expression will match the 8 because it's at the end of the line. When you're searching for lines that match a regular expression exactly no extra text at the start or end , use both anchors.
For instance, if you want to make sure a line consists only of digits, enter:. We wanted to take you just far enough to get a sense of what regular expressions can do for you.
There are many, many more features, but some of them are useful only in programming languages. As we warned before, different tools support different features, so you have to read the documentation for egrep, Sed, or any other tool or language to find out what works there.
When you're testing regular expressions, you can try lots of online or stand-alone tools some offered gratis and some for sale that help debug problems such as mismatched brackets and parentheses. Such tools can help you learn the more complex features and make complex regular expressions easier to write.
Regular Expressions When you're looking through files or trying to change text, your needs are often ambiguous or approximate. Typical searches include: Finding an indeterminate number of things, such as "one or more zeroes". Finding text that can have variants, such as "color" and "colour", or "gray" and "grey". Extracting parts of text that forms a pattern.
For instance, suppose you have a list of email addresses such as somebody fsf. Plain text A regular expression doesn't have to be fancy.
Indeterminate quantities One simple application of regular expressions is to search for "any number" of something, or a fuzzy amount such as "3 to 5" hyphens. Ferruccio Ferruccio Thanks a lot. Exactly the kind of answer I was hoping for : — Damien Golding. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.
Email Required, but never shown. The Overflow Blog. Stack Gives Back Safety in numbers: crowdsourcing data on nefarious IP addresses. Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Related I just created a file "hi. Then cmd allows me to run it directly by typing "hi" from command line. So if it is not possible with batch script, then i may use a VB script trough batch.
Download coreutils too while you're at it. I've written a free command line tool for Windows to do this. It's called rxrepl , it supports Unicode and file search. Some may find it a useful tool. The Scripting Guy covers how to do this in PowerShell no additional downloads on most recent Windows OSs, you probably already have it installed.
This supports. I've found fnr. It has GUI and command-line. ECMA regex is not quite as powerful as the. NET regex available to powershell, but it is still pretty darn good. And I think the average user will find this utility easier to use than powershell.
The built-in JREPL options already provide a lot of inherent power, but the ability to inject user supplied JScript really opens up amazing possibilities. I developed the script because my workplace does not allow downloading of non-standard exe files, but has no restriction on writing batch or JScript scripts Read the subsequent posts from that thread for examples of usage and development history.
Two good choices are either Cygwin which will give you a Unix-like, bash-like environment alternative to cmd. In either package, see 'sed', 'awk', and 'grep'. You can also use GSAR to perform command line search and replace.
Works with hex and binary as well. It will not do the complex heavy lifting that regex can perform, but for basic search and replace, it does the job quickly and easily. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Regex Replace from Command line Ask Question.
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