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

learn more… | top users | synonyms (1)

103
votes
5answers
83k views

What is the difference between `grep`, `egrep`, and `fgrep`?

Can any one tell me the technical difference between grep and egrep, and fgrep and provide a suitable example? When do I need to use grep over egrep and vice versa?
78
votes
5answers
191k views

How do I grep for multiple patterns?

I want to find all lines in several files that match one of two patterns. I tried to find the patterns I'm looking for by typing grep (foo|bar) *.txt but the shell interprets the | as a pipe and ...
53
votes
4answers
41k 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 ...
47
votes
6answers
68k views

How can I use sed to replace a multi-line string?

I've noticed that, if I add \n to a pattern for substituting using sed, it does not match. Example: $ cat > alpha.txt This is a test Please do not be alarmed $ sed -i'.original' 's/a test\nPlease ...
46
votes
2answers
44k 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.
32
votes
4answers
27k views

How to use find command to search for multiple extensions

I can get all jpg images by using: find . -name "*.jpg" But how can I add png files to the results as well?
28
votes
1answer
2k views

Why does my regular expression work in X but not in Y?

I wrote a regular expression which works well in a certain program (grep, sed, awk, perl, python, ruby, ksh, bash, zsh, find, emacs, vi, vim, gedit, …). But when I use it in a different program (or on ...
27
votes
5answers
20k views

How to diff files ignoring comments (lines starting with #)?

I've two configuration files, the original from the package manager and a customized one modified by myself. I've added some comments to describe behavior. How can I run diff on the configuration ...
21
votes
6answers
7k views

Regex for all 10 letter words, with unique letters

I am trying to write a regex that will display all words that are 10 characters long, and none of the letters are repeating. So far, I have got grep --colour -Eow '(\w{10})' Which is the very ...
17
votes
11answers
4k 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 ...
16
votes
6answers
10k views

How can you combine all lines that end with a backslash character?

Using a common command line tool like sed or awk, is it possible to join all lines that end with a given character, like a backslash? For example, given the file: foo bar \ bash \ baz dude \ happy ...
15
votes
2answers
19k views

How to run grep with multiple AND patterns?

I would like to get the multi pattern match with implicit AND between patterns, i.e. equivalent to running several greps in a sequence: grep pattern1 | grep pattern2 | ... So how to convert it to ...
14
votes
7answers
4k views

Software for visually building regular expressions?

I frequently need to create regular expressions for use in scripts (mostly when used in sed), however, I find, sometimes the regular expressions get very complicated and difficult for me to understand ...
13
votes
5answers
1k views

How to remove the (1) from filenames using the find command

I recently converted all of my FLAC files to a lower sampling rate of 44.1 kHz and bit depth of 24 bits (because iPhone/iPod don't support anything above that) using XLD on my Mac OS 10.7 (Lion). ...
13
votes
4answers
56k views

Finding text between two specific characters or strings

Say I have lines like this: *[234]* *[23]* *[1453]* where * represents any string (except a string of the form [number]). How can I parse these lines with a command line utility and extract the ...
13
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?
13
votes
6answers
500 views

/bin/dash: check whether $1 is a number

What would be the best way to check whether $1 is an integer in /bin/dash ? In bash, I could do: [[ $1 =~ ^([0-9]+)$ ]] But that does not seem to be POSIX compliant and dash does not support that
12
votes
3answers
2k views

Why does [a-z] asterisk match numbers?

I have 3 directories at current path. $ls a_0db_data a_clean_0db_data a_clean_data $ls a_*_data a_0db_data: a_clean_0db_data: a_clean_data: $ls a_[a-z]*_data a_clean_0db_data: a_clean_data: I ...
12
votes
3answers
4k views

Online grep exercises?

Are there any online grep tutorials that would feature some online tool for performing exercises? For example, having some predefined text sample and being told what patterns to find and so forth? It ...
11
votes
7answers
21k views

How can I “grep” patterns across multiple lines?

It seems I am misusing grep/egrep. I was trying to search for strings in multiple line and could not find a match while I know that what I'm looking for should match. Originally I thought that my ...
11
votes
6answers
832 views

How can I grep a directory based on the contents of two successive lines?

How can I grep a directory for lines that contain "Foo", but only get matches when the next line also contains "Bar"?
11
votes
4answers
2k views

How do I choose specific files in a different directory using bash?

I want to list (or delete, or do some other operation) on certain files in a directory, like this: $ ls /opt/somedir/ aa bb cc aa.txt bb.txt cc.txt $ ls /opt/somedir/(aa|bb|cc) ## pseudo-bash ...
11
votes
2answers
14k views

Grep 'OR' regex problem

I am trying to use grep with a regex to find lines in a file that match 1 of 2 possible strings. Here is my grep: $ grep "^ID.*(ETS|FBS)" my_file.txt The above grep returns no results. However if I ...
11
votes
2answers
9k views

Regular expression in bash script

This is my first time bash scripting so I'm probably making an easy mistake. Basically, I'm trying to write a script that gets the groups of a user, and if they are in a certain group, it will log ...
11
votes
1answer
7k views

Substitute text with sed and keep part of the original text

I am trying to convert <id>1</id> <Name>ENTERPRISE RESOURCE PLANNING</Name> to: <column name="id">1</column> <column name="Name">ENTERPRISE RESOURCE ...
10
votes
4answers
31k views

grep lines starting with “1” in Ubuntu

I try to search for lines that start with "1" using ls -1 | grep ^1* but it returns lines that do not start with 1. What I am missing here?
10
votes
1answer
11k views

Replace using VIM, reuse part of the search pattern

I am working with VIm and trying to set up a search and replace command to do some replacements where I can re-use the regular expression that is part of my search string. A simple example would be a ...
10
votes
1answer
7k views

What is the .gitignore pattern equivalent of the regex (Big|Small)(State|City)-[0-9]*\.csv

I have a regex I stuck in my .gitignore similar to: (Big|Small)(State|City)-[0-9]*\.csv It didn't work so I tested it against RegexLab.NET. I then found the gitignore man page which led me to ...
10
votes
3answers
13k views

grep: Trailing backslash

I want to do a grep for \resources\. How do I do this? I've tried: grep \resources\ grep \\resources\\ grep "\resources\" grep "\\resources\\" None of these work.
10
votes
2answers
949 views

grep: display filename once, then display context with line numbers

Our source code has error codes scattered throughout. Finding them is easy with grep, but I'd like a bash function find_code that I can execute (eg. find_code ####) which will provide output along ...
9
votes
3answers
1k views

Strange behaviour of “ls -a | grep ^\.”

I wanted to list the content of a pwd and display only file starting with dot. I tried ls -a | grep ^\. but I cannot figure out why the output contains also the files which do not start with dot. For ...
9
votes
2answers
580 views

In VIM, replace path with slashes without using escape slashes

In vim I want to substitute a long path /a/b/f/g/d/g with another /s/g/w/d/g/r in a text file. Usually I use \/ but there are too many slashes here. Is there an easier way?
9
votes
3answers
16k 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?
9
votes
2answers
827 views

What is the definition of a regular expression?

I recently got into a friendly argument with Ghoti about what constitutes a regular expression in the comments to my answer to this question. I claimed that the following is a regular expression: ...
9
votes
7answers
981 views

How to merge text of alphabetic lines with the numeric lines in shell?

I Have a file that has text like this: AAAA BBBB CCCC DDDD 1234 5678 9012 3456 EEEE 7890 etc... And i want to match up the Alphabetic lines with the Numeric lines so they are like this: ...
9
votes
4answers
525 views

Regular expression using \\ vs using \

Why does grep e\\.g\\. <<< "this is an e.g. wow" and grep e\.g\. <<< "this is an e.g. wow" do the same thing? If I add a third slash, it also has the same result. BUT, once I ...
9
votes
2answers
1k views

Match word containing characters beyond a-zA-Z

To match a word one can use \v(\w+) From the vim help :h \w: \w word character: [0-9A-Za-z_] This works exactly as described in the manual. However, I want to match words that contain ...
8
votes
6answers
2k views

Delete lines beginning with #

How do I delete lines beginning with a #, given that there can be whitespace on the left and right of the #? # Master socket provides access to userdb information. It's typically
8
votes
7answers
678 views

How can I “merge” patterns in a single line?

I am doing grep and sed and I get 2 lines of a file that I am interested in. How can I get these lines in a single line ending with the new line character? Now I am getting: pattern1 pattern2 ...
8
votes
3answers
9k views

How can I grep for this or that (2 things) in a file?

I have a file that has "then"'s and "there"'s. I can $ grep "then " x.x x and then some x and then some x and then some x and then some and I can $ grep "there " x.x If there is no blob none ...
8
votes
3answers
433 views

VIM see regular expressions matches as you type

If I type /regex then the cursor temporarily jumps to the first match and all matches are highlighted. This updates as I type. Is it possible to get this behavior when I'm getting ready to make a ...
7
votes
3answers
3k views

Print all lines which not containing punctuation

I want a regex pattern which can print all lines which not containing punctuation : Input : .This is line 1 This is ! line 2 This is line (3) This is line 4 Output: ( should be) This is line 4 ...
7
votes
1answer
190 views

Grep search returning a different line

This is my grep search grep 'Invoker_Slark*' true_pairscore.txt But it returns the line Invoker_Slardar. Even though the file contains Invoker_Slark. Why is that?
7
votes
3answers
262 views

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 ...
7
votes
2answers
3k views

Number of backslashes needed for escaping regex backslash on the command-line

I recently had trouble with some regex on the command-line, and found that for matching a backslash, different numbers of characters can be used. This number depends on the quoting used for the regex ...
7
votes
4answers
6k views

How to grep for pipe |

How can I grep for line containing pipe character | or for character >: files content: |this is test where is > this is none now what I need using grep command is grep -iE "<some ...
7
votes
4answers
4k views

Recursively rename subdirectories that match a regex

I have a media server with a folder called Series. (/media/Expansion2/Series/) In it, I have (surprise!) TV series. These are just the show names, e.g., /media/Expansion2/Series/The Big Bang Theory/ ...
7
votes
1answer
397 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 ...
7
votes
3answers
629 views

vim regex not need \ to escape

In Vim is there an option to write regexs in the same style as Awk for example/sp\{0,\}/ Would be /sp{0,}/
7
votes
3answers
506 views

How to use [\w]+ in regular expression in sed?

I am on Windows, but I guess my question is still rightly placed here. C:\Users\User>grep --version GNU grep 2.6.3 C:\Users\User>sed --version GNU sed version 4.2.1 I noticed that the ...