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

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How do you save a complex regex for multiple reuse in sed?

In using sed, I often create rather complicated and intricate regexes that I need to match twice in a file. Is there a way for me to save this regex and just reference it twice? Maybe something that ...
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328 views

How do I use the regular pattern operator {m,n} in grep?

I have a text file, from which I need to select only those lines, which include the string "tt". So I tried this on the command line: grep "t{2}" textfile Allthough I know the textfile contains ...
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Strategy to extract movies's name from this ununiform dataset?

I am working on a movie database problem to improve regular expressions, this is the problem I'm running into. My dataset looks like this: Movie Name (variable space and tabs) year Movie1(can ...
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How to use regex as field separator in awk?

I'm trying to use regex as a field seperator in awk. From my reading this seems possible but I can't get the syntax right. rpm -qa | awk '{ 'FS == [0-9]' ; print $1 }' awk: cmd. line:1: { FS awk: ...
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Regex alternation/or operator (foo|bar) in GNU or BSD Sed

I cannot seem to make it work. GNU sed documentation says to escape the pipe, but that doesn't work, nor does using a straight pipe without the escape. Adding parens makes no difference. $ echo ...
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How to use regex with AWK for string replacement?

Suppose there is some text from a file: (bookmarks ("Chapter 1 Introduction 1" "#1" ("1.1 Problem Statement and Basic Definitions 23" "#2") ("Exercises 31" "#30") ("Notes and References 42" "#34")) ) ...
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find words with all vowels in order from a file

I have a large dictionary file with 300,000+ words in it and I'm trying to find all words with the vowels aeiou in that order and have only exactly 5 vowels. My current attempt does not seem to be ...
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Why do I have to escape a “dot” twice?

I know that we can escape a special character like *(){}$ with \ so as to be considered literals. For example \* or \$ But in case of . I have to do it twice, like \\. otherwise it is considered ...
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sed one-liner to delete everything between a pair of brackets?

I am working with some text that is full of stuff between brackets [] that I don't want. Since I can delete the brackets myself, I don't need the one-liner to do that for me, but I do need a one-liner ...
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261 views

Why two almost idetical grep commands return different output: w/o and with filename

I have 2 almost identical greps: [Alex@localhost tmp]$ grep /bin/bash /etc/passwd root:x:0:0:root:/root:/bin/bash AlexL:x:500:500::/home/AlexL:/bin/bash user1:x:501:501:user1 ...
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Removing Color Codes From Output [duplicate]

Possible Duplicate: Removing control chars (including console codes / colours) from script output I'm working on a script to work alongside a program that I'm writing. What i'm trying to do ...
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Why isn't sed greedy in this simple case?

$echo "foo 65 bar" | sed -n -e 's/.*\([0-9]\+\).*/\1/p' 5 Why is the output not 65? Shouldn't sed greedily match the [0-9]\+ part? How do I tell sed to match all of 65?
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grep for words of no more than a certain length

I'm looking for a way to grep things like: i log for E M, i 1 f x i 0, I xi 1, 3 1,. simply based on number of characters. Nothing in that hypothetical output is longer than three characters. This ...
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In a regular expression, which characters need escaping?

In general, which characters in a regular expression need escaping? For example, the following is not syntactically correct: echo '[]' | grep '[]' grep: Unmatched [ or [^ This, however, is ...
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Why can't I escape the braces “]” in sed?

Question: Why can't I escape the "]"? $ printf "*#$@~\!&*()[]\n" *#~\!&*()[] $ printf "*#$@~\!&*()[]\n" | sed 's/[*#$@~!&*()\[\]]//g' *#~\!&*() $
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Replace uppercase to lowercase except first letter of each word in specific line

I want to replace names that I received in uppercase letters only. The names are mixed with other information which should stay as it is. AUTH: at the beginning of the line identifies it as a line ...
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180 views

Extracting subset of lines of a file based on regex for first & last line

I have a large text file and I only want to look at some of the lines. The first line I want matches a regex R, and when the line matches the regex S, I don't care about that line, or any following ...
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Grep for range of numbers [duplicate]

How would you search a log file for a date range? Log file looks like this: 01/14 00:00:01 INFO: received connect request from 10.10.10.10 I need to condense the log to 10 minutes starting ...
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Using Modifiers of Perl-compatible Regex (PCRE) in grep

According to grep --help and man grep, we can use the -P option in order to interpret the pattern as a Perl regular expression (PCRE, to be precise), instead of the default POSIX basic regular ...
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Regex `/pattern/g` and ed `:g/pattern/`: which came first, and why `g`?

The g option (e.g. s/pattern/replacement/g) for many tools that use regex-style pattern matching and the :g command in ed, ex, vi, and vim have pretty similar usage and meaning: match the given regex ...
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What is the meaning of this test expression []? [duplicate]

I've seen someone use command: ps -ef | grep [h]ttpd and Output is: apache 25125 31006 0 21:54 ? 00:00:00 /usr/sbin/httpd apache 26869 31006 0 22:04 ? 00:00:00 ...
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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 ...
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How to replace a word with new line

I have a text file with following data and each row ends with |END|. T|somthing|something|END|T|something2|something2|END| I am tryig to replace |END| with \n new line with sed. sed ...
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Replace a character except last x occurences

I have a file that has a bunch of hostnames correlated with IPs that looks like this: x-cluster-front-1 192.168.1.2 x-cluster-front-2 192.158.1.10 y-cluster-back-1 10.1.11.99 y-cluster-back-2 ...
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extract part of string using sed

ls lib/oracle-11.2.0.3.0.txt | sed 's/lib.\([oracle.*]\)\.txt/\1/' It is giving the whole string instead of just oracle part until .txt What am I doing wrong? I can do it using awk as follows, but, ...
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Using sed to find and replace complex string (preferrably with regex)

I have a file with the following contents: <username><![CDATA[name]]></username> <password><![CDATA[password]]></password> ...
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grep: regex only for match anything between parenthesis

How do I match word only between parenthesis Input : this is (test.com) Desire Output : test.com
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674 views

difference between .* and * in regular Expression

I've a file named "test" that contains linux Unixlinux Linuxunix it's linux l...x now when i use grep '\<l.*x\>' , it matches : linux it's linux l...x but when i use grep '\<l*x\>' ...
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How to remove dot and space from beginning of filenames

I'm trying to change jpg files named with a dot and a space at the beginning and with a missing dot before the end (like this . Startjpg to Start.jpg The dot makes the files hidden from sed and ls ...
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Negative lookbehind/ahead assertions in Linux less pager (or vim)

I want to find all instances of "index" not followed by .php in a log using less. /index(?!\.php) does not work. Is this possible? What is the regex for less and vim (do they differ?). Is this not ...
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“parentheses not balanced” even though I escaped it?

Im trying to run this simple sed command sed '/VALUES\ \([0-9]/d!' It still gives me an error saying "RE error: parentheses not balanced" (yes the quotes are there). What can I do? I mean I could ...
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History of Bash globbing

Is there a historical reason why Bash "globbing" and regular expressions are not identical? For example, I believe that in Bash [1-2]* matches anything that starts with a 1 or a 2 followed by anything ...
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How to tell “grep -w” what characters make up “words”?

$ printf 'asf .test. afd\nasaf foo-test asfdads\n' asf .test. afd asaf foo-test asfdads $ printf 'asf .test. afd\nasaf foo-test asfdads\n' | grep -w test asf .test. afd asaf foo-test asfdads ...
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grep for multiple regexes, and count the number of occurences

Say, I have a file, and multiple regexes have to be searched in it and the number of matches for each regex has to be counted. Thus, I cannot combine the patterns: grep -Po ...
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vim search numbers containing specific number of digits

I need to find specific length numbers in a big document. I tried to use regex for this. For example, If I need to search for numbers with exactly 2 digits, I use /d/d (i.e. /d twice followed by a ...
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remove duplicate files

On my Mac OS X 10.6.7, iTunes duplicated every single file in my music library. Now I have 3,840 files instead of 1,920. The problem is that iTunes didn't simply duplicate the whole folder, but each ...
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AWK - how to reduce the greed of a regular expression?

I have an example: echo "@article{gjn2010jucs, Author = {Grzegorz J. Nalepa}, " | awk '{ sub(/@.*,/,""); print }' Is it possible to write a regular expression that selects the shorter pattern? ...
5
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1answer
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How can I match the page break character in a regular expression?

Nano calls it ^L, but of course, typing something like $ grep -v "^\^L" file doesn't work. Its unicode codepoint is 000C. How can I match it in a regular expression?
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What regular expression engine type does bash use?

I use RegEx Buddy to prototype and debug my regular expressions. RegEx Buddy allows me to choose between a number of different regular expression engine types (.NET, Java, Perl, GNU BRE, GNU ERE, ...
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309 views

Execute a command within 'sed'

I have a list of random memory addresses saved in a text file, and I need to sed them out, decode them, and save them back to my file. However, the decoding operation I'm trying to perform is handled ...
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exact match in regrex when using vim, man, or less

when using vim, man, or less, I want to do some exact match in regrex for example, when using man, I want to check the argument '-c' if I use /'-c' the matching could be -cim ...
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Regexp in .ssh/config

At work, I often have to log into hosts which follow a common naming scheme, e.g. qc01 - qc12, hc01 - hc10, and so on. All of these need to get the same config values in my laptop's .ssh/config. Of ...
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Regex & Sed/Perl: Match word that ISN'T preceded by another word

I'd like to use sed or perl to replace all occurrences of a word that doesn't have a certain word in front of it. For example, I have a text file that contains a plot of a movie and I want to replace ...
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What does \bi\b mean in a grep pattern?

What does this command do? grep "\bi\b" linux.txt What is it searching for?
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Emacs simple arithmetics in query replace

Is it possible to do the following in emacs: Query replace all numbers in a region by the number +n, for example if you have: 12 and 7 are nice numbers let n be 3, then it should transform to 15 ...
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The ERE regex to split() string between a delimiter and end-of-word

I'm using a long gawk 3.1.6 script to do a complex conversion of Zim markdown text into GtkDialog code and am stuck on the following problem... Sample ASCII input... [[link|label label]] [[link]] ...
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Lowercase all but the first (Uppercase) letter from UPPERCASE in cyrillic

To make all letters a lower case except the first letter. The first letter would look like "Uppercase" after I changed (from UPPERCASE in cyrillic). The rest (not UPPERCASED) leave unchanged. I'm ...
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1answer
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Renaming files to have lower case extensions with 'rename'

I'm trying to currently rename a large set of files and have been using quite kludgy methods to do so, such as: rename 's:(.*)\.MOV:$1.mov:g' *.MOV rename 's:(.*)\.JPG:$1.jpg:g' *.JPG What I'd ...
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syntax of ls --hide= and ls --ignore=

ls --hide and ls --ignore provides the possibility leave out files defined through regular expressions set after the --ignore= part. The latter makes sure that this option isn't turned off via -a, -A. ...
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Pattern Matching Exclude Duplicate Characters

Is there a regular expression for the following that matches characters in a character set but only once? In other words, once a character is found, remove it from the set. If grep cannot do this, ...