All Questions
Tagged with quoting regular-expression
13
questions
806
votes
13
answers
1.8m
views
How do I grep for multiple patterns with pattern having a pipe character?
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 ...
- 9,532
72
votes
11
answers
235k
views
Checking if an input number is an integer
I'm trying to check if an input is an integer and I've gone over it a hundred times but don't see the error in this. Alas it does not work, it triggers the if statement for all inputs (numbers/letters)...
- 2,093
13
votes
2
answers
5k
views
Why do I need to escape regex characters in sed to be interpreted as regex characters?
It seems e.g.
cat sed_data.txt | sed 's/\b[0-9]\{3\}\b/NUMBER/g'
that I must escape characters to form a regular expression. In this case I had to escape braces in order to be interpreted as a number ...
- 10.2k
57
votes
2
answers
114k
views
grep and escaping a dollar sign
I want to know which files have the string $Id$.
grep \$Id\$ my_dir/mylist_of_files
returns 0 occurrences.
I discovered that I have to use
grep \$Id$ my_dir/mylist_of_files
Then I see that the $...
- 4,185
10
votes
3
answers
17k
views
shell test whether multiple lines string contains specified pattern in last line
I want to determine whether a multi-line string ends with a line containing specified pattern.
These code failed, it doesn't match.
s=`echo hello && echo world && echo OK`
[[ "$s" =~ ...
- 325
10
votes
4
answers
6k
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 ...
- 101
10
votes
3
answers
51k
views
Why can't find -regex match a newline?
Why does this fail?
touch "$(printf "a\nb")"; find . -regex './.\n.'
I also tried these, none of which work:
find . -regextype posix-extended -regex '.\n.'
find . -regextype posix-awk -regex '.\n.'
...
- 245k
6
votes
3
answers
2k
views
Why does my grep expression need to use $'string' to match tab characters?
If you take this code:
echo -e '\t\t\tString' | grep '^[\t]*String'
the result is blank because it doesn't match, yet this:
echo -e '\t\t\tString' | grep $'^[\t]*String'
works. I swear that I must ...
- 2,182
17
votes
2
answers
24k
views
Why do I have to escape a "dot" twice?
I know that we can escape a special character like *(){}$ 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 ...
- 770
13
votes
2
answers
13k
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 (...
- 9,557
8
votes
3
answers
33k
views
Escaping * with Regular Expressions and Grep
I have a file that has unique lines that start with 2 stars (**).
However when I run a grep command for
grep \*\* fileName
I get all of the lines in the file. This is very unusual, and what I see ...
- 743
5
votes
1
answer
7k
views
command: ls /etc | sort | grep d* is yielding no results but ls /etc | sort | grep p* lists entire directory
I am playing around with piping and grep tonight. I know that grep uses regex and that * means 0 or more occurrences of the preceding character. So the way I understand it is that if I do the ...
- 51
1
vote
0
answers
2k
views
Why use a variable in a bash regex match inside [[? [duplicate]
There is not a simple answer to this question at this site yet.
This question aims to give a simple and clear answer.
It is usually recommended to use a variable ($regex) in this construct:
if [[ $...
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