What are grep, fgrep, egrep?<\/p>\n\n\n\n
grep<\/code> \u2013 General Pattern Search (Basic Regular Expressions)<\/h2>\n\n\n\n1)grep command:-(global regular expression print)<\/p>\n\n\n\n
\n- Uses Basic Regular Expressions (BRE)<\/strong><\/li>\n\n\n\n
- Most commonly used command<\/li>\n<\/ul>\n\n\n\n
Syntax<\/h3>\n\n\n\ngrep \"pattern\" file_name\n<\/code><\/pre>\n\n\n\nExample<\/h3>\n\n\n\ngrep \"unix\" notes.txt\ngrep \"m\" a.txt\ngrep \"M\" a.txt\ngrep -i \"M\" a.txt #case insensitive\ngrep -c \"M\" a.txt #line count\ngrep -n \"M\" a.txt #line number\ngrep -w \"MM\" a.txt # word \n\ngrep -f a.txt b.txt #mathching of two file\ngrep -L \"unix\" * #file names that matches & pattern\n\n<\/code><\/pre>\n\n\n\n🔹 Searches lines containing unix<\/strong><\/p>\n\n\n\nUsing regex<\/h3>\n\n\n\ngrep \"^u\" notes.txt\n<\/code><\/pre>\n\n\n\n🔹 Lines starting with u<\/code><\/p>\n\n\n\n
\n\n\n\n2️⃣ fgrep<\/code> \u2013 Fixed String Search (Fast & Simple)<\/h2>\n\n\n\n2)fgrep command:-fixed-character strings in a file<\/p>\n\n\n\n
\n- No regular expressions<\/strong><\/li>\n\n\n\n
- Searches exact words or strings<\/strong><\/li>\n\n\n\n
- Faster for plain text<\/li>\n<\/ul>\n\n\n\n
Syntax<\/h3>\n\n\n\nfgrep \"pattern\" file_name\n<\/code><\/pre>\n\n\n\nExample<\/h3>\n\n\n\nfgrep \"unix|linux\" notes.txt\nfgrep \"mm\" a.txt\nfgrep -c \"m\" a.txt #line number\nfgrep \"m\" *.txt\nfgrep -l \"@a\" a.txt #print filename\nfgrep -n \"@a\" a.txt #print line number\nfgrep -x \"a\" a.txt #display only lines matched entirely.\n<\/code><\/pre>\n\n\n\n🔹 Searches the exact text<\/strong> unix|linux<\/code>
(Not OR condition)<\/p>\n\n\n\n✅ Best when:<\/p>\n\n\n\n
\n- You don\u2019t want regex<\/li>\n\n\n\n
- You want speed<\/li>\n<\/ul>\n\n\n\n
\n\n\n\n3️⃣ egrep<\/code> \u2013 Extended Regular Expressions<\/h2>\n\n\n\n\n- Uses Extended Regular Expressions (ERE)<\/strong><\/li>\n\n\n\n
- Supports
|<\/code>, +<\/code>, ?<\/code>, ()<\/code><\/li>\n<\/ul>\n\n\n\nSyntax<\/h3>\n\n\n\negrep \"pattern\" file_name\n<\/code><\/pre>\n\n\n\nExample<\/h3>\n\n\n\negrep \"unix|linux\" notes.txt\negrep \"mital\" * #globally search\negrep \"m\" a.txt\negrep -c \"mm\" a.txt #linenumber mathched\negrep -l \"mm\" a.txt # print filename\negrep -n \"mm\" a.txt # print linenumber\negrep -r \"m*\" m.txt\negrep -r \"m*\" . #recursively searching whole root\n<\/code><\/pre>\n\n\n\n🔹 Matches unix OR linux<\/strong><\/p>\n\n\n\negrep \"(cat|dog)s?\" animals.txt\n<\/code><\/pre>\n\n\n\n🔹 Matches cat<\/code>, cats<\/code>, dog<\/code>, dogs<\/code><\/p>\n\n\n\n
\n\n\n\n🔁 Key Differences (Very Important for Exams)<\/h2>\n\n\n\nFeature<\/th> grep<\/th> fgrep<\/th> egrep<\/th><\/tr><\/thead> Pattern type<\/td> Basic Regex<\/td> Fixed string<\/td> Extended Regex<\/td><\/tr> Supports `<\/td> ` (OR)<\/td> ❌<\/td> ❌<\/td><\/tr> Supports +<\/code>, ?<\/code>, ()<\/code><\/td>❌<\/td> ❌<\/td> ✅<\/td><\/tr> Fastest<\/td> ❌<\/td> ✅<\/td> ❌<\/td><\/tr> Most flexible<\/td> ❌<\/td> ❌<\/td> ✅<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
\n\n\n\n⚠️ Important Note (Modern UNIX\/Linux)<\/h2>\n\n\n\n
Today:<\/p>\n\n\n\n
\nfgrep<\/code> = grep -F<\/code><\/li>\n\n\n\negrep<\/code> = grep -E<\/code><\/li>\n<\/ul>\n\n\n\nExamples<\/h3>\n\n\n\ngrep -F \"unix|linux\" file.txt\ngrep -E \"unix|linux\" file.txt\n<\/code><\/pre>\n\n\n\n
\n\n\n\n📝 Easy Memory Trick<\/h2>\n\n\n\n\n- grep<\/strong> \u2192 basic search<\/li>\n\n\n\n
- fgrep<\/strong> \u2192 fixed text (no regex)<\/li>\n\n\n\n
- egrep<\/strong> \u2192 extra power (OR, +, ?)<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
What are grep, fgrep, egrep? 1️⃣ grep \u2013 General Pattern Search (Basic Regular Expressions) 1)grep command:-(global regular expression print) Syntax Example 🔹 Searches lines containing unix Using regex 🔹 Lines starting with u 2️⃣ fgrep \u2013 Fixed String Search (Fast & Simple) 2)fgrep command:-fixed-character strings in a file Syntax Example 🔹 Searches the exact text […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-386","post","type-post","status-publish","format-standard","hentry","category-unix"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=\/wp\/v2\/posts\/386","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=386"}],"version-history":[{"count":1,"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=\/wp\/v2\/posts\/386\/revisions"}],"predecessor-version":[{"id":387,"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=\/wp\/v2\/posts\/386\/revisions\/387"}],"wp:attachment":[{"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=386"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=386"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mitalgoswami.in\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=386"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}