Regular expressions are a means of matching a pattern of characters within a string.

learn more… | top users | synonyms (1)

2
votes
3answers
2k views

sed one-liner to delete any line that begins with a digit

Pretend I am working with this file. The beginning of the first visible line is obscured, so ignore that. 43 is the beginning of the next line, and that line would be deleted. The next line (which ...
45
votes
4answers
27k views

Can grep output only specified groupings that match?

Say I have a file: # file: 'test.txt' foobar bash 1 bash foobar happy foobar I only want to know what words appear after "foobar", so I can use this regex: "foobar \(\w\+\)" The parenthesis ...
12
votes
4answers
3k views

Replacing Multiple blank lines with a single blank line in vim / sed

Question more or less says it all. I'm aware that /^$/d will remove all blank lines, but I can't see how to say 'replace two or more blank lines with a single blank line' Any ideas?
0
votes
2answers
339 views

Why does this regex find a match for \x63 with a pattern [\80-\BF]

I am trying to filter valid/invalid UTF-8 bytes, but I get strange results from the following regex (which is intended to handle a 3 byte form of UTF-8). I have intended the pattern should not ...
3
votes
2answers
186 views

Why isn't this sed regex matching?

I've recently started learning sed. I did $seq 10 | sed '/[^049]/d' I was expecting 4 9 10 as output. But I got 4 9 Where am I making mistake in understanding this regex?
3
votes
1answer
3k views

Grep - ^(\s*$) vs ^\s*$

I want to search for a field that only has spaces. When counting, this two commands gave me different results: grep "^\s*$" -E -c grep "^(\s*$)" -E -c Another thing. What is the correct way to say ...
1
vote
1answer
318 views

Easy Regex on Apache Logs

I'm struggling to create a regex for Apache logs. It's for ignoreregex on Fail2ban. I'd really like to be able to put something like /house to catch all files in that directory or ...
4
votes
2answers
1k views

substrings and regexps

I have a string contained in a variable, and I want to extract substrings based on position relative to another substring. My solution seems to work unless the string is sent to a function as an arg. ...
3
votes
2answers
652 views

ANDed conditional using regexp and variables

I want to test whether a line, read in from a file, has a specific beginning AND an ending containing a word held in a variable. Here's some code: The input file is: line one #; line two #; line ...
6
votes
3answers
12k views

What does \? mean in a regular expression?

The following command is used to search for a 7-digit phone number: grep "[[:digit:]]\{3\}[ -]\?[[:digit:]]\{4\}" file What does \? stand for?
6
votes
2answers
2k views

Print specific Exif image data values with exiv2

How do I print the image Exif date with a tool like exiv2? My goal is to write the image year and month into separate variables. Do I really have to parse the output with regex or is there a ...
4
votes
1answer
318 views

Trouble with grep -o regex

I'm trying to use a grep command with the --only-matching flag, but it's not behaving as I would expect it to. This command: echo "1/2/3/4/5" | grep -oE "^([^/]+/){0,2}" Gives this output: 1/2/ ...
2
votes
3answers
801 views

Filtering paths to a specific depth

I'm using rsync and the flags -nPaAXz ~/ to check which files are going to be copied. This is far too verbose to make any sense of. How could I filter the output so I view the list of files/folders ...
3
votes
1answer
3k views

Bash regex matching not working in 4.1

Upgraded to Bash4 and found that it is not matching regexes: $ echo $BASH_VERSION 4.1.2(1)-release $ [[ "20110228" =~ "^[0-9]{8}$" ]] && echo matches But Bash 3.0 is: $ echo $BASH_VERSION ...
3
votes
2answers
2k views

sed or tr one-liner to delete all numeric digits

So, I have this textfile, and it consists of mostly alphanumeric characters. It's a standard document. But since I copied it and pasted it from a PDF, there are page numbers in there. I don't much ...
3
votes
2answers
745 views

Using grep/sed/awk to classify log file entries

I need to process a very large log file with many lines in different formats. My goal is to extract unique line entries who have the same starting pattern, e.g. '^2011-02-21.*MyKeyword.*Error', ...
7
votes
1answer
375 views

Why do some regex commands have opposite intepretations of '\' with various characters?

Take, for example, this command: find . -regex ".*\.\(cpp\|h\)" This will find all the .h and .cpp files in your directory. The period character '.' in regular expressions usually means "any ...
14
votes
10answers
3k views

There must be a better way to replace single newlines only?

I am in the habit of writing one line per sentence because I typically compile things to LaTex, or am writing in some other format where line breaks get ignored. I use a blank line to indicate the ...
1
vote
4answers
2k views

Processing control characters

I have a log file which contains a bunch of non visible control characters such as hex \u0003. I would like to replace this using something like SED, but can't get the first part of the regex to ...
3
votes
1answer
292 views

Ex and Vi: buffers and regexes

I want to put regex matches to buffer but cannot get even simpler example y :.put myNewBuffer return msg [line] [put] [buffer] working ie how to put something to buffer? So to regular expressions ...
2
votes
2answers
400 views

lookbehind and using it with grep in Vi?

Trying to get into Vi (not Vim), after learning Vim. Vim has a lookabehind like /\(Not this\)\@<!$, how to do it in Vi? If I want to search recurvively down directory in Vim, I could do :vimgrep ...
4
votes
2answers
439 views

How to find files with names having a long string after the first dot

My Samsung Galaxy S doesn't like files where the name contains a long string after the first dot. I guess some part of the software has a too short buffer for the file extension. How can I find all ...
3
votes
4answers
2k views

Applying a regex to stdin

In programing we often see the use of Regular Expressions. One of the most common forms is: newText = text.replace( /regex/, 'replacementString' ) If stdin is text and stdout is newText, what ...
43
votes
2answers
38k views

Find files with certain extensions

How can I use find to find all files that have a .xls or .csv extension? I have seen a -regex option but I don't know how to use it.