Using grep, you can quickly find text matching a regular expression in a single file, a group of files, or text coming from stdin.<\/p>\n\n\n\n
The most common way to find text in a Linux system is using the command-line utility Using This article covers how to use the The most basic way to use Notice that [ Download the Linux grep command cheat sheet<\/a>. ]<\/em><\/strong><\/p>\n\n\n\n In the previous example, when you searched for To avoid that, you can use regular expressions to be more specific about what you’re looking for. For example, to find only lines that start with the word This time You can also use extended<\/em> regular expressions with the command-line parameter You can also look for lines that end with a text pattern by using the Regular expressions are a big part of Similar to finding text patterns in a single file, you can use When you use multiple files, [ Keep your most commonly used commands handy with the Linux commands cheat sheet<\/a>. ]<\/em><\/strong><\/p>\n\n\n\n To run the search recursively in multiple subdirectories, use the command line flag The Similar to other Unix utilities, For example, if you want to check whether the package You can filter long command outputs with [ Get the guide to installing applications on Linux<\/a>. ]<\/em><\/strong><\/p>\n\n\n\n The For a complete list of The GNU grep utility is flexible and useful, helping you accomplish many tasks in your daily sysadmin activities. The more you use Using grep, you can quickly find text matching a regular expression in a single file, a group of files, or text coming from stdin. The most common way to find text in a Linux system is using the command-line utility grep. This utility was originally developed for the Unix operating system in the early 1970s. Grep … <\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,4],"tags":[],"class_list":["post-55","post","type-post","status-publish","format-standard","hentry","category-linux","category-pi"],"_links":{"self":[{"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/55","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=55"}],"version-history":[{"count":0,"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/55\/revisions"}],"wp:attachment":[{"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=55"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=55"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dsslit.ddns.net\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=55"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}grep<\/code>. This utility was originally developed for the Unix operating system in the early 1970s. Grep evolved over the years, and the most common version available today for Linux, GNU grep, has additional features such as colored output. However, its main functionality is still the same.<\/p>\n\n\n\ngrep<\/code>, you can quickly find text matching a regular expression<\/a> in a single file, a group of files, or text coming from stdin<\/code><\/a> using the shell pipe operator.<\/p>\n\n\n\ngrep<\/code> command to find text.<\/p>\n\n\n\nFind text in a file<\/h2>\n\n\n\n
grep<\/code> is searching for text in a single file. To do this, type grep<\/code> followed by the text pattern to search for and the file name to search in. For example, to find which port the Secure Shell (SSH) daemon uses, search for Port<\/code> in file \/etc\/ssh\/sshd_config<\/code>:<\/p>\n\n\n\n$ grep Port \/etc\/ssh\/sshd_config\nPort 22\n#GatewayPorts no<\/em><\/code><\/pre>\n\n\n\ngrep<\/code> finds all lines that match the text pattern regardless of where the pattern is located.<\/p>\n\n\n\nExtend grep with regular expressions<\/h2>\n\n\n\n
Port<\/code> in the SSH configuration file, grep<\/code> returned two lines. The line you were looking for, Port 22<\/strong>, and an additional line containing the search pattern. In some cases, that’s exactly what you want. In other cases, grep<\/code> could find too many entries that you’re not interested in, requiring you to sort through them to find the desired information.<\/p>\n\n\n\nPort<\/code>, you can use the regular expression operator ^<\/code>, like this:<\/p>\n\n\n\n$ grep ^Port \/etc\/ssh\/sshd_config\nPort 22<\/code><\/pre>\n\n\n\ngrep<\/code> returned only the line that started with Port<\/code> since, in the second line, the expression Port<\/code> is in the middle.<\/p>\n\n\n\n-E<\/code>. For example, to search for a pattern that contains the word Port<\/code> followed by numbers, use this regular expression:<\/p>\n\n\n\n$ grep -E \"Port [1-9]+\" \/etc\/ssh\/sshd_config\nPort 22<\/code><\/pre>\n\n\n\n$<\/code> operator. For example, to find all lines that end with none<\/code> in sshd_config<\/code>, use grep<\/code> like this:<\/p>\n\n\n\n$ grep none$ \/etc\/ssh\/sshd_config\n#RekeyLimit default none<\/em>\n#AuthorizedPrincipalsFile none<\/em>\n#AuthorizedKeysCommand none<\/em>\n#ChrootDirectory none<\/em>\n#VersionAddendum none<\/em>\n#Banner none<\/em><\/code><\/pre>\n\n\n\ngrep<\/code>, making it powerful and flexible. However, regular expressions are a huge topic. For additional information, look at Regular expression on Wikipedia<\/a> or Regular expressions 101<\/a>.<\/p>\n\n\n\nFind text in multiple files and directories<\/h2>\n\n\n\n
grep<\/code> to find text in multiple files or directories. To find text in multiple files simultaneously, specify which files to search from after the first file name, or use a shell wildcard such as *<\/code> for all files. For example, to search for a configuration in two files:<\/p>\n\n\n\n$ grep Port \/etc\/ssh\/sshd_config \/etc\/ssh\/ssh_config\n\/etc\/ssh\/sshd_config:Port 22\n\/etc\/ssh\/sshd_config:#GatewayPorts no<\/em>\n\/etc\/ssh\/ssh_config:# Port 22<\/em><\/code><\/pre>\n\n\n\ngrep<\/code> shows the name of the file where it found a match before showing the matched line.<\/p>\n\n\n\n-R<\/code>:<\/p>\n\n\n\n$ grep -R ^Port \/etc\n\/etc\/ssh\/sshd_config:Port 22<\/code><\/pre>\n\n\n\ngrep<\/code> command is fast and returns results quickly, but it may take a long time if you specify too many files or subdirectories to search.<\/p>\n\n\n\nFind text in another command’s output<\/h2>\n\n\n\n
grep<\/code> also acts on stdin<\/code> when you pipe the output of another command into it. This is a fast and useful way to filter a command’s output to match the text pattern you’re looking for.<\/p>\n\n\n\nopenssh<\/code> is installed in your Fedora or Red Hat Enterprise Linux (RHEL)<\/a> operating system, you can pipe the output of command rpm -qa<\/code>, which lists all installed packages, into grep<\/code> to search for the pattern:<\/p>\n\n\n\n$ rpm -qa | grep ssh\nlibssh-config-0.9.6-4.fc36.noarch\nlibssh-0.9.6-4.fc36.x86_64\nopenssh-8.8p1-1.fc36.1.x86_64<\/code><\/pre>\n\n\n\ngrep<\/code>, making finding useful information easier.<\/p>\n\n\n\nAdditional useful options<\/h2>\n\n\n\n
grep<\/code> command provides many options to change how it searches for patterns or displays results. So far in this article, you’ve seen some of them. While I can’t list all options, here are some other useful examples:<\/p>\n\n\n\n\n
-i<\/code> for a case-insensitive search.<\/li>\n\n\n\n-v<\/code> to invert the search and display lines that do not match the pattern.<\/li>\n\n\n\n-w<\/code> to search for entire words only instead of patterns in the middle of other words.<\/li>\n\n\n\n--color<\/code> for colored output, making it easier to spot the matched pattern.<\/li>\n<\/ul>\n\n\n\ngrep<\/code> options, consult the man pages.<\/p>\n\n\n\nWhat’s next?<\/h2>\n\n\n\n
grep<\/code>, the more comfortable you will become, and soon you’ll notice you’re relying on it all the time.<\/p>\n","protected":false},"excerpt":{"rendered":"