{"id":244,"date":"2026-10-13T02:10:53","date_gmt":"2026-10-13T02:10:53","guid":{"rendered":"http:\/\/www.scmgalaxy.com\/tutorials\/2010\/04\/16\/unix-command-grep\/"},"modified":"2026-10-13T02:10:54","modified_gmt":"2026-10-13T02:10:54","slug":"unix-command-grep","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/unix-command-grep\/","title":{"rendered":"Unix grep Quick Reference: Patterns, Options, and Real Command Examples"},"content":{"rendered":"\n

grep<\/strong> is the standard Unix text-search command for finding lines that match a pattern in one or more files. This guide helps DevOps engineers, sysadmins, and shell users quickly choose the right grep options and write safer, more predictable search commands.<\/p>\n\n\n\n

Originally published on 2010-04-16; fully revised and updated.<\/em><\/p>\n\n\n\n

\"unix-command-grep\"<\/p>\n\n\n\n

grep syntax at a glance<\/h2>\n\n\n\n

The base form is pattern-first, then one or more files. If no file is provided, grep reads from standard input.<\/p>\n\n\n

grep [options] 'pattern'<\/span> file1 [file2 ...]\n\n# stdin example<\/span>\njournalctl -u sshd | grep -i 'failed'<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Most useful grep options (quick comparison)<\/h2>\n\n\n\n
Option<\/th>What it does<\/th>Example<\/th><\/tr><\/thead>
-i<\/td>Ignore case during matching<\/td>grep -i ‘agarwal’ emp.lst<\/td><\/tr>
-v<\/td>Invert match (show lines that do not match)<\/td>grep -v ‘director’ emp.lst<\/td><\/tr>
-n<\/td>Show line numbers with matched lines<\/td>grep -n ‘marketing’ emp.lst<\/td><\/tr>
-c<\/td>Count matching lines (not total match occurrences)<\/td>grep -c ‘director’ emp.lst<\/td><\/tr>
-l<\/td>List only filenames that contain at least one match<\/td>grep -l ‘manager’ *.lst<\/td><\/tr>
-e<\/td>Add multiple patterns on the command line<\/td>grep -e ‘Agarwal’ -e ‘aggarwal’ emp.lst<\/td><\/tr>
-f<\/td>Read patterns from a file (one pattern per line)<\/td>grep -f pattern.lst emp.lst<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
How grep evaluates a search request<\/h2>\n\n\n\n
\nflowchart TD\n    A[Choose input files or stdin] --> B[Choose pattern source]\n    B --> C[Inline pattern]\n    B --> D[Pattern file with -f]\n    C --> E[Apply options like -i -v -n]\n    D --> E\n    E --> F{Any matching lines}\n    F -- yes --> G[Print selected output]\n    F -- no --> H[Return nonzero status]\n<\/pre>\n\n\n\n
This flow is useful in scripts: grep output gives you the matching lines, and grep exit status can drive conditional logic.<\/p>\n\n\n\n
Practical command examples<\/h2>\n\n\n
# Basic single-file search<\/span>\ngrep 'sales'<\/span> emp.lst\n\n# Search across multiple files<\/span>\ngrep 'director'<\/span> emp1.lst emp2.lst\n\n# Phrase search (quoted pattern)<\/span>\ngrep 'jai sharma'<\/span> emp.lst\n\n# Variable expansion inside double quotes<\/span>\ngrep \"jai Sharma $var\"<\/span> emp.lst\n\n# Ignore case<\/span>\ngrep -i 'agarwal'<\/span> emp.lst\n\n# Exclude matching lines and write remaining lines to a new file<\/span>\ngrep -v 'director'<\/span> emp.lst > other.list<\/span>\n\n# Show line numbers<\/span>\ngrep -n 'marketing'<\/span> emp.lst\n\n# Count matching lines<\/span>\ngrep -c 'director'<\/span> emp.lst\n\n# Show only filenames with matches<\/span>\ngrep -l 'manager'<\/span> *.lst<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n
# Multiple patterns from CLI<\/span>\ngrep -e 'Agarwal'<\/span> -e 'aggarwal'<\/span> -e 'agarwal'<\/span> emp.lst\n\n# Patterns from a file (one per line)<\/span>\ngrep -f pattern.lst emp.lst<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Common pitfalls and best practices<\/h2>\n\n\n\n
  • Quote patterns that contain spaces or shell-special characters.<\/li>
  • Use -i<\/strong> when case is uncertain instead of manually duplicating case variants.<\/li>
  • Remember: -c<\/strong> counts matching lines<\/em>, not every repeated occurrence on a line.<\/li>
  • Use -f<\/strong> for long pattern lists; it is cleaner and easier to review than many -e<\/strong> flags.<\/li>
  • When redirecting output, use a clear filename (for example, other.list<\/em>) to avoid shell parsing issues with unquoted spaces.<\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"
    grep is the core Unix command for searching text by pattern across files or standard input. This revised quick reference covers syntax, high-value options, and practical examples you can use immediately.<\/p>\n","protected":false},"author":1,"featured_media":4369,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_joinchat":[],"footnotes":""},"categories":[4957],"tags":[4126,333,475,4124,4128,4129,4131,4130,4121,4123,169,4125,4127,4122],"class_list":["post-244","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-linux","tag-basic-grep-commands","tag-command","tag-grep","tag-grep-command-line-options","tag-grep-unix-command-guide","tag-grep-unix-command-introduction","tag-grep-unix-command-overview","tag-grep-unix-command-quick-reference","tag-grep-unix-commands-with-examples","tag-how-to-use-grep","tag-unix","tag-unix-command-grep-examples","tag-unix-grep-command-match-pattern","tag-unix-grep-command-options"],"_links":{"self":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/244","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/comments?post=244"}],"version-history":[{"count":4,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/244\/revisions"}],"predecessor-version":[{"id":79074,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/posts\/244\/revisions\/79074"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media\/4369"}],"wp:attachment":[{"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/media?parent=244"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/categories?post=244"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devopsschool.com\/blog\/wp-json\/wp\/v2\/tags?post=244"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}