{"id":1902,"date":"2017-03-23T18:44:27","date_gmt":"2017-03-23T13:14:27","guid":{"rendered":"https:\/\/www.wikitechy.com\/technology\/?p=1902"},"modified":"2017-03-28T17:51:26","modified_gmt":"2017-03-28T12:21:26","slug":"difference-grep-egrep-fgrep","status":"publish","type":"post","link":"https:\/\/www.wikitechy.com\/technology\/difference-grep-egrep-fgrep\/","title":{"rendered":"BASH – What is the difference between `grep`, `egrep`, and `fgrep`?"},"content":{"rendered":"

Grep:<\/strong><\/span><\/h4>\n
    \n
  • Grep (Global Regular Expression Print) is a command-line utility for searching plain-text data sets for lines matching a regular expression. … Grep was originally developed for the Unix operating system, but is available today for all Unix-like systems.<\/li>\n<\/ul>\n

    egrep<\/span><\/strong><\/h4>\n
      \n
    • egrep is an acronym for “Extended Global Regular Expressions Print”. It is a program which scans a specified file line by line, returning lines that contain a pattern matching a given regular expression. The standard egrep command looks like: egrep <flags> ‘<regular expression>’ <filename><\/li>\n<\/ul>\n

      fgrep<\/span><\/strong><\/h4>\n
        \n
      • The fgrep command differs from the grep and egrep commands because it searches for a string instead of searching for a pattern that matches an expression.<\/li>\n
      • The fgrep command uses a fast and compact algorithm. The $, *, [, … , (, ), and \\ characters are interpreted literally by the fgrep command.<\/li>\n<\/ul>\n[ad type=”banner”]\n

        difference between `grep`, `egrep`, and `fgrep`:<\/strong><\/span><\/h4>\n

        grep:<\/span><\/strong><\/h4>\n
          \n
        • grep is an acronym that stands for “Global Regular Expressions Print”. grep is a program which scans a specified file or files line by line, returning lines that contain a pattern.<\/li>\n
        • A pattern is an expression that specifies a set of strings by interpreting characters as meta-characters.<\/li>\n
        • For example the asterisk meta character (*) is interpreted as meaning “zero or more of the preceding element”.<\/li>\n
        • This enables users to type a short series of characters and meta characters into a grep command to have the computer show us what lines in which files match.<\/li>\n<\/ul>\n

          The standard grep command looks like:<\/span><\/strong><\/h4>\n
          Bash Code<\/span> <\/div> 
          grep <flags> '<regular expression>' <filename><\/code><\/pre> <\/div>\n
          grep prints the search results to the screen (stdout) and returns the following exit values:<\/strong><\/span><\/p>\n
          0 A match was found.
          \n1 No match was found.
          \n>1 A syntax error was found or a file was inaccessible
          \n(even if matches were found).<\/p>\n
          Some common flags are: -c for counting the number of successful matches and not printing the actual matches, -i to make the search case insensitive, -n to print the line number before each match printout, -v to take the complement of the regular expression (i.e. return the lines which don’t match), and -l to print the file names of files with lines which match the expression.<\/p>\n
          egrep<\/span><\/strong><\/h4>\n
            \n
          • egrep is an acronym that stands for “Extended Global Regular Expressions Print”.<\/li>\n
          • The ‘E’ in egrep means treat the pattern as a regular expression. “Extended Regular Expressions” abbreviated ‘ERE’ is enabled in egrep. egrep (which is the same as grep -E) treats +, ?, |, (, and ) as meta-characters.<\/li>\n
          • In basic regular expressions (with grep), the meta-characters ?, +, {, |, (, and ) lose their special meaning. If you want grep to treat these characters as meta-characters, escape them \\?, \\+, \\{, \\|, \\(, and \\).<\/li>\n
          • For example, here grep uses basic regular expressions where the plus is treated literally, any line with a plus in it is returned.<\/li>\n<\/ul>\n
             
             Bash Code<\/span> <\/div> 
            grep "+" myfile.txt<\/code><\/pre> <\/div>\n[ad type=”banner”]\n
            egrep on the other hand treats the “+” as a meta character and returns every line because plus is interpreted as “one or more times”.<\/p>\n
             
             Bash Code<\/span> <\/div> 
            egrep "+" myfile.txt<\/code><\/pre> <\/div>\n
            Here every line is returned because the + was treated by egrep as a meta character. normal grep would have searched only for lines with a literal +.<\/p>\n
            fgrep<\/strong><\/span><\/h4>\n
              \n
            • fgrep is an acronym that stands for “Fixed-string Global Regular Expressions Print”.<\/li>\n
            • fgrep (which is the same as grep -F) is fixed or fast grep and behaves as grep but does NOT recognize any regular expression meta-characters as being special. The search will complete faster because it only processes a simple string rather than a complex pattern.<\/li>\n<\/ul>\n
              For example, if you wanted to search you .bash_profile for a literal dot (.) then using grep would be difficult because you would have to escape the dot because dot is a meta character that means ‘wild-card, any single character’:<\/p>\n
               
               Bash Code<\/span> <\/div> 
              grep "." myfile.txt<\/code><\/pre> <\/div>\n
              The above command returns every line of myfile.txt. Do this instead:<\/strong><\/span><\/h4>\n
               
               Bash Code<\/span> <\/div> 
              fgrep "." myfile.txt<\/code><\/pre> <\/div>\n
              Then only the lines that have a literal ‘.’ in them are returned. fgrep helps us not bother escaping our meta characters.<\/p>\n[ad type=”banner”]\n","protected":false},"excerpt":{"rendered":"
              Grep: Grep (Global Regular Expression Print) is a command-line utility for searching plain-text data sets for lines matching a regular expression. … Grep was originally developed for the Unix operating system, but is available today for all Unix-like systems. egrep egrep is an acronym for “Extended Global Regular Expressions Print”. It is a program which […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1699],"tags":[4081,4070,4082,4083,4069,4074,4086,4075,4085,4084,4072,4077,4068,4071,4079,4078,4080,4073,4076],"class_list":["post-1902","post","type-post","status-publish","format-standard","hentry","category-linux","tag-egrep","tag-egrep-empty-subexpression-when-attempting-to-filter-out-words-from-a-list","tag-and-fgrep","tag-difference-between-grep-and-egrep","tag-egrep-regular-expression-for-times-over-five-minutes","tag-fgrep","tag-fgrep-match-patterns-in-a-file","tag-find-and-grep-commands","tag-grep","tag-grep-and-egrep-regular-expressions","tag-grep-template-for-extracting-lines-where-second-word-has-only-two-vowels","tag-how-can-i-grep-for-a-string-containing-regex-metacharacters-like-and","tag-how-to-filter-content-between-specific-keywords-using-grep","tag-how-to-get-numbers-of-specified-range-of-length-from-string-with-grep","tag-how-to-use-restricted-characters-in-egrep","tag-using-grep-command-and-backreferencing","tag-what-is-the-difference-between-grep","tag-what-is-the-difference-between-egrep","tag-what-is-the-difference-between-grep-e-and-grep-e-option"],"_links":{"self":[{"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/posts\/1902","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/comments?post=1902"}],"version-history":[{"count":0,"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/posts\/1902\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/media?parent=1902"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/categories?post=1902"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.wikitechy.com\/technology\/wp-json\/wp\/v2\/tags?post=1902"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}