Here is a quick example of a situation where you might want to use GREP. Suppose you wanted to find out which text files in your current directory contained the string "Bob". You would type:

grep Bob *.txt 

GREP responds with a list of the lines in each file (if any) that contained the string "Bob". Because GREP does not ignore case by default, the strings "bob" and "boB" do not match.  

GREP can do a lot more than match a single, fixed string. You can make GREP search for any string that matches a particular pattern. (See GREP: The search string.)

The general command-line syntax for GREP is

grep [-<options>] <searchstring> [<files(s)>...]

To display a list of the GREP command line options, special characters, and defaults for GREP, enter:

grep ?

GREP Command Line Options

If you find that the results of your GREP are longer than one screen, you can redirect the output to a file.  

For example, you could use this command:

GREP "Bob" *.txt > temp.txt 

This command searches all files with the TXT extension in the current directory, then puts the results in a file called TEMP.TXT. (You can name this file anything you like.) Use any word processor to read TEMP.TXT (the results of the search).

You can pass options to the GREP utility on the command line by specifying one or more single characters preceded by a hyphen (-). Each individual character is a switch that you can turn on or off: A plus symbol (+) after a character turns the option on; a hyphen (-) after the character turns the option off. The + sign is optional; for example, -r means the same thing as -r+. You can list multiple options individually (like this: -i -d -l), or you can combine them (like this: -ild or -il, -d, and so on).  

Here are the GREP option characters and their meanings:  

Command Line Options for GREP  

The value of <searchstring> defines the pattern GREP searches for. A search string can be either a regular expression or a literal string.  

• In a regular expression, certain characters have special meanings: They are operators that govern the search. (A regular expression is either a single character or a set of characters enclosed in brackets. A concatenation of regular expressions is a regular expression.)
• In a literal string, there are no operators: Each character is treated literally.

You can enclose the search string in quotation marks to prevent spaces and tabs from being treated as delimiters. To search for an expression that begins with "-", use the -e option. The text matched by the search string cannot cross line boundaries; that is, all the text necessary to match the pattern must be on a single line.  

When you use the -r option (on by default), the search string is treated as a regular expression (not a literal expression).  

The following characters have special meanings:

Four of the "special" characters ($, ., *, and +) do not have any special meaning when used within a bracketed set. In addition, the character ^ is only treated specially if it immediately follows the beginning of the set definition (immediately after the [ delimiter).

Example 1

grep -r "[^a-z]main\ *\(" *.c 

Matches:

main(i,j:integer) 
if (main ()) halt; 
if (MAIN ()) halt;

Does Not Match:

mymain() 

Explanation: The search string tells GREP to search for the word main with no preceding lowercase letters ([^a-z]), followed by zero or more occurrences of blank spaces (\ *), then a left parenthesis. Since spaces and tabs are normally considered command-line delimiters, you must quote them if you want to include them as part of a regular expression.  

Example 2  

grep -ri [a-c]:\\data\.fil *.c *.inc

Matches:

A:\data.fil
B:\DATA.FIL
c:\Data.Fil

Does Not Match:

d:\data.fil a:data.fil  

Explanation: Because the backslash (\) and period (.) characters usually have special meaning in path and file names, you must place the backslash escape character immediately in front of them if you want to search for them. The -i option is used here, so the search is not case sensitive.  

Example 3l  

grep "search string with spaces" *.doc *.c

Matches:

A search string with spaces in it.

Does not match

This search string has spaces in it.

Explanation: This is an example of how to search for a string containing specific text.  

Example 4  

grep -rd "[ ,.:?'\"]"$ \*.doc

Matches:

He said hi to me.
Where are you going?
In anticipation of a unique situation,
Examples include the following:
"Many men smoke, but fu man chu."Explanation

Does not match:

He said "Hi" to me
Where are you going? I'm headed to the

Explanation: This example searches for any one of the characters " . : ? ' and , at the end of a line. The double quote within the range is preceded by an escape character so it is treated as a normal character instead of as the ending quote for the string. Also, the $ character appears outside of the quoted string. This demonstrates how regular expressions can be concatenated to form a longer expression.  

Example 5  

grep -w[=] = *.c

Matches:

i = 5;
j=5;
i += j; 

Does not match:

if (i == t) j++;
/* ==================================== */ 

This example redefines the current set of legal characters for a word as the assignment operator (=) only, then does a word search. It matches C assignment statements, which use a single equal sign (=), but not equality tests, which use a double equal sign (==).

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