If a pattern is to be searched in all the files in some directory, * can be used in shells which supports glob or alternatively, -r option of grep can be used which would search in all files in the directory recursively. The -f option specifies a file where grep reads patterns.

When you use file.txt, you're actually using relative path. Lines not containing a pattern are printed with grep -v: grep -v pattern file.txt. To get only the line number (without the matching line), one may use cut: grep -n pattern file.txt cut -d : -f 1. On the other hand, relative paths are ideal if the folder you want to search in is in the current directory or the subdirectory of the current directory. Line numbers are printed with grep -n: grep -n pattern file.txt. With its unusual name, you may have guessed that grep is an acronym. It is used for finding a search patterns in the content of a given file. For example, when I'm currently in $HOME/Desktop and I want to access files from c in /mnt, then I'll use absolute path, i.e., /mnt/c. This can be used to specify multiple search patterns, or to protect a pattern beginning with a hyphen (-). Grep is a command line utility in Unix and Linux systems.

The syntax is: grep . grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a.

grep -f patternfile filetomatch In our example, we’ve created pattern file names pattern.txt with the below contents: cat pattern.txt This It. Without passing any option, grep can be used to search for a pattern in a file or group of files. The file should contain one pattern per line.

Absolute path generally starts with the root of the file system hierarchy, i.e., / and relative path starts with the name of sub-directory in the current directory that contains the files.Ībsolute paths are ideal when you're currently in different hierarchy. Instead of writing it down every time, you can specify a list of patterns in a file and use with -f flag. You can provide absolute path or relative path of the file.

Use of grep command in linux