grep for special characters in Unix

Question

I have a log file (application.log) which might contain the following string of normal & special characters on multiple lines:

*^%Q&$*&^@$&*!^@$*&^&^*&^&

I want to search for the line number(s) which contains this special character string.

grep '*^%Q&$*&^@$&*!^@$*&^&^*&^&' application.log

The above command doesn't return any results.

What would be the correct syntax to get the line numbers?

`^@` : means `^` followed by `@` or nul character? – Nahuel Fouilleul Sep 12 '12 at 12:19 — Nahuel Fouilleul, Sep 12 '12 at 12:19

score 213 · Accepted Answer · edited Dec 21 '13 at 08:30

213

Tell grep to treat your input as fixed string using -F option.

grep -F '*^%Q&$*&^@$&*!^@$*&^&^*&^&' application.log

Option -n is required to get the line number,

grep -Fn '*^%Q&$*&^@$&*!^@$*&^&^*&^&' application.log

edited Dec 21 '13 at 08:30

Zombo

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answered Sep 12 '12 at 12:04

Prince John Wesley

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Depending your version of grep you only need to escape (with a backslash) `^`, `$`, `.`, `*` and `\ `. or you can try `fgrep`, too. – Nahuel Fouilleul Sep 13 '12 at 07:33
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@NahuelFouilleul: +1. btw, `fgrep` is same as `grep -F`. – Prince John Wesley Sep 13 '12 at 08:18
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@PrinceJohnWesley: it's the same but on some systems there are many versions of grep so using fgrep may find the version which support -F – Nahuel Fouilleul Sep 13 '12 at 09:34
What if he use `egrep '*^%Q&$*&^@$&*!^@$*&^&^*&^&' application.log` ? – inckka Jul 18 '14 at 13:18
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Doesn't work. `grep -rinF '-static'` prints `Invalid option «t»`. The @Mani's [answer worked](http://stackoverflow.com/a/12406009/2388257), i.e. `grep -rin "\-static"`. – Hi-Angel Aug 31 '14 at 18:39
Did not work for me on MacOs. Maybe considering specifying your environment in the answer? – Jacob Waters Oct 30 '21 at 05:55
Did not work on Ubuntu 20.04.5 with `grep -Fn '#!/usr/bin/python' --include=*.py`, no any output shown and seems stucked in console. – Keelung Mar 21 '23 at 02:35

score 128 · Answer 2 · edited Dec 21 '13 at 08:30

128

The one that worked for me is:

grep -e '->'

The -e means that the next argument is the pattern, and won't be interpreted as an argument.

From: http://www.linuxquestions.org/questions/programming-9/how-to-grep-for-string-769460/

edited Dec 21 '13 at 08:30

Zombo

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answered Apr 18 '13 at 13:12

The Student

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str='! " # $ % & ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~' ; echo "$str" | grep -e "$str" ..... NOT WORKING, what worked for you didn't had enough special characters besides switch sign '-', but win -F instead of -e is WORKING ! – THESorcerer Oct 25 '15 at 08:52
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The only thing works for me, even '\' or -F or fgrep do not work. Thanks! – user180574 Aug 13 '18 at 19:17
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This should be the accepted answer - simple and works for grep – Ishay Peled Dec 12 '18 at 22:26
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Tried -F and fgrep doesn't work for me when searching a string include '-' char. This works. – 世界知名伟人 Jan 25 '19 at 06:53
I'm wondering why this answer is present in this question (https://stackoverflow.com/q/12387685 for reference to Q&A I'm currently viewing) - probably a wrong case of answers getting merged from another question? To search for patterns starting with `-`, see also https://stackoverflow.com/questions/2427913/how-can-i-grep-for-a-string-that-begins-with-a-dash-hyphen – Sundeep May 18 '20 at 10:36
please mark this one as the accepted answer. The -F option (currently marked as the accepted doesnot work) – OAH May 15 '21 at 07:28
This works, not -F, not fgrep. Tested on MacOS Catalina – auspicious99 Oct 23 '21 at 14:59
This works for me on a Mac – Jacob Waters Oct 30 '21 at 05:54
trying to find all pointers of pointers in the c file with `grep -e "->*->" a.c` doesn't seem to work . the * picks up all sorts of garbage. any suggestions ? – Jay D Jan 29 '23 at 22:00

ryenus · Answer 3 · 2016-09-14T01:06:57.623

A related note

To grep for carriage return, namely the \r character, or 0x0d, we can do this:

grep -F $'\r' application.log

Alternatively, use printf, or echo, for POSIX compatibility

grep -F "$(printf '\r')" application.log

And we can use hexdump, or less to see the result:

$ printf "a\rb" | grep -F $'\r' | hexdump -c
0000000   a  \r   b  \n

Regarding the use of $'\r' and other supported characters, see Bash Manual > ANSI-C Quoting:

Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as specified by the ANSI C standard

score 3 · Answer 4 · edited Dec 21 '13 at 08:30

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grep -n "\*\^\%\Q\&\$\&\^\@\$\&\!\^\@\$\&\^\&\^\&\^\&" test.log
1:*^%Q&$&^@$&!^@$&^&^&^&
8:*^%Q&$&^@$&!^@$&^&^&^&
14:*^%Q&$&^@$&!^@$&^&^&^&

edited Dec 21 '13 at 08:30

Zombo

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answered Sep 13 '12 at 12:14

Mani

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score 2 · Answer 5 · edited Feb 10 '17 at 21:45

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You could try removing any alphanumeric characters and space. And then use -n will give you the line number. Try following:

grep -vn "^[a-zA-Z0-9 ]*$" application.log

edited Feb 10 '17 at 21:45

Marvin Rabe

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answered Feb 10 '17 at 20:52

R. Kumar

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Thanks.. It's works good for me to find the special characters from a file. – Dipankar Nalui Jun 28 '18 at 04:36

score -4 · Answer 6 · answered Mar 02 '17 at 16:48

Try vi with the -b option, this will show special end of line characters (I typically use it to see windows line endings in a txt file on a unix OS)

But if you want a scripted solution obviously vi wont work so you can try the -f or -e options with grep and pipe the result into sed or awk. From grep man page:

Matcher Selection -E, --extended-regexp Interpret PATTERN as an extended regular expression (ERE, see below). (-E is specified by POSIX.)

   -F, --fixed-strings
          Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched.  (-F is specified
          by POSIX.)

In what way this is better than an accepted answer so you added it to almost 5-years old question? — SergGr, Mar 02 '17 at 17:13

grep for special characters in Unix

6 Answers6

A related note

Linked