Find, Locate, and Grep

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FIND

Find is a linux search tool that can be used to find a variety of files based on the given criteria.

Basic find

find targetdirectory -name stringtofind

find / -name hello.txt

wildcards

find / -name "*.txt"

Discard errors (ie permission denied)

find / -name "*.txt" 2>/dev/null

 Find files with specific permissions

Find files with read,write, and execute permissions

find / -perm +rwx

Find files by size

Find files that are greater than 2MB:

find / -size +2M

Find files that are less than 2MB:

find / -size -2M

Find files that are exactly 2MB:

find / -size 2M

Find files by owner/group

Find files based on group

find / -group groupname

Find files based on owner

find / -user username

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LOCATE

Locate is similar to find in its functionality, but it operates quite differently. Locate performs quick searches using its own mlocate database - a database of files that are stored on a server. The database needs to be regularly updated in order for the locate command to work accurately.

Update mlocate DB

updatedb

Locate file based on name

locate [options] test.txt

Option	Function
-r	Search file names using regex
-c	Count the number of matching entries found
-e	Return only files that exist at the time of the search
-i	Ignore casing
--n [number of entries]	Retirn the first few matches up to the specified number.

Additional configuration for locate command

The mlocate database used by the locate command is stored at;
/var/lib/mlocate/mlocate.db

The configuration for this database is stored at;
/etc/updatedb.conf

Within this config file, you can add exclusions for directories to be skipped within the mlocate DB, this is done using the below syntax;
PRUNEPATH = "/path/to/exclude"

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 GREP

string2withina file, if both are found then both will be outputted.

grep 'string1|string2' filename

-searchfilesrecursively 

grep -r hello /

(beforebelowwillshowthebeforethestring

grep -B2 string filename

You can also combine these to see the lines before and after

grep -A2 -B2 string filename

Option	Function
-i	Case insensitive
-v	Exclude string
'string|string'	OR Statement - case insensitive As with all of Linux, grep is case sensitive. The -i flag can be passed to ignore case type. -v -exclude string The -v flag is used to exclude a string from an output. | - or statement The below will search for string1multiple orstrings.
-r	Recursive
-A & -B	After and& after)Before Sometimes- you might wantused to search forspecify a string,number and see theof lines before/either before or after thata string. The below will show the 2 lines following the string grep -A2specified string filename is Thefound.
-E	Extended 2Regular linesExpression.

-E or egrep - extendedExtended regular expression

Regular expression is essentially the methodology that we can use to manipulate grep to find advanced string patterns.

Special characters

When trying to grep for special characters, you need to make sure to 'escape' those characters, this is done by proceeding special characters with a \:

grep -E year\'s

Beginning and end of line

line begins with

The below example would show any lines beginning with the character '1'

grep -E "^1" filename

line ends with

The below example would show any lines ending with the character '1'

grep -e "1$" filename

Ranges

grep interprets ranges that are defined through square brackets []. 

line begins with 1 and is followed by numbers in the 0-2 range:

grep -E "^1[0-2]" filename

We can also search for ranges of letters

The below command would search for the letter b, proceeded by any letter in the specified range, followed by the letter g:

grep -E "b[aeiou]g" filename

We can also search a range of letters like this:

grep -E "b[a-z]g" filename

You can also combine ranges

grep -E "b[a-z,A-Z]g" filename

Wildcards

There are a number of wildcard options available to use in egrep.

. - any single character

grep -e "c.t" filename

• Matches: "cat", "cot", "cut", etc.
• Does not match: "ct", "caat"

* - matches zero or more occurrences of the preceding character

grep -e "g*d" filename

• Matches: "gd", "god", "good", "goood"
• Does not match: "go", "goooo", "gdo", "goddy"

.* - match zero or more of any character

grep -e "a.*b" filename

• Matches: "ab", "acb", "axyzb", "a123b"
• Does not match: "a b", "ab ", "acbd", "a"

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