The program's name derives from the command used to perform a similar operation, using the Unix text editor ed:
This command searches a file globally for lines matching a given regular expression, and prints them.
There are various command line switches available when using grep that modify this default behavior including printing lines which do not match, finding or excluding files to search, and annotating the output in various ways. There are also multiple modern implementations of the classic Unix grep, each with a unique feature set.
This is an example of a common grep usage:
grep apple fruitlist.txt
Grep would return, in this case, all of the lines in file fruitlist.txt with at least one instance of 'apple' in them. Keep in mind that grep would not return lines with 'Apple' (capital A) because by default grep is case sensitive. Like most Unix commands grep accepts flags which can be used to change this and many other behaviors. For example:
grep -i apple fruitlist.txt
This would return all lines with the words 'apple', 'Apple', 'apPLE', or any other mixing of capital and lower case.Linux has a -r switch in grep command to search for a string in all the files in a directory tree. In Solaris you can use this command to do the same:
find . -type f -print | xargs grep -li "find me"