He took the name from the ed command string g/re/p, which translates as "global regular expression search. The above command will try to find a string func main () in all the files in a particular directory and also in the subdirectories as well. For that we make use of the command shown below. Thompson spent about an hour that evening making his tool a general utility that could be used by others and renamed it as grep. In the above command replace the word placeholder with. He needed a tool that could search for phrases and strings within text files. McMahon was trying to identify the authors of the Federalist papers through textual analysis. His department head at Bell Labs, Doug Mcilroy, approached Thompson and described the problem one of his colleagues, Lee McMahon, was facing. Ken Thompson had extracted the regular expression search capabilities from the ed editor ( pronounced ee-dee) and created a little program - for his own use - to search through text files. The first two are bang on the third is slightly off. The following example shows how to search through all. Interestingly, POSIX grep is not required to support -r (or -R ), but I'm practically certain that System V grep did, so in practice they (almost) all do. To search for all the lines of a file that do not contain a certain string, use the -v option to grep. Thirdly, it was written overnight to satisfy a particular need. -r is for recursive -e is optional but its argument specifies the regex to search for. Secondly, the wealth of options can be overwhelming. The grep command is famous in Linux and Unix circles for three reasons. It also works with piped output from other commands. The Linux grep command is a string and pattern matching utility that displays matching lines from multiple files.
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