{"id":401,"date":"2009-08-04T15:00:51","date_gmt":"2009-08-04T22:00:51","guid":{"rendered":"http:\/\/www.stuartsheldon.org\/blog\/?p=401"},"modified":"2009-08-04T15:00:51","modified_gmt":"2009-08-04T22:00:51","slug":"using-regular-expressions-on-the-linux-command-line","status":"publish","type":"post","link":"https:\/\/www.stuartsheldon.org\/blog\/2009\/08\/using-regular-expressions-on-the-linux-command-line\/","title":{"rendered":"Using Regular Expressions On The Linux Command Line"},"content":{"rendered":"

Using Regular Expressions (RegEx) on the command line.<\/strong><\/em><\/h2>\n

Questions about regular expressions come up at the Lug meetings on a regular basis. Here are some examples of regex commands I use all the time. Hope you find them useful.<\/p>\n

<\/p>\n

Parse a file skipping commented lines.<\/em><\/strong><\/h2>\n
gateway:~# egrep '^[^#]' \/etc\/manpath.config\r\nMANDATORY_MANPATH\t\t\t\/usr\/man\r\nMANDATORY_MANPATH\t\t\t\/usr\/share\/man\r\nMANDATORY_MANPATH\t\t\t\/usr\/local\/share\/man\r\n[...] more lines\r\n\r\n#### Let's use to wordcount to count the lines returned:\r\n\r\ngateway:~# egrep '^[^#]' \/etc\/manpath.config | wc -l\r\n23\r\n\r\ngateway:~# cat \/etc\/manpath.config | wc -l\r\n114<\/pre>\n
So let’s look at the command. The egrep command is just grep that allows regex searches. So it will search through a file and when it finds a match to the regex, it will return the entire line that contains that match. It returns nothing if there is no match on that line. Our regex is ‘^[^#]’<\/strong><\/em> , which reads like this:<\/p>\n