4.2. grep Examples with Regular Expressions
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4.2. grep Examples with Regular ExpressionsThe following datafile , used for the examples in this section, is repeated periodically for your convenience.
Example 4.5.% grep NW datafile northwest NW Charles Main 3.0 .98 3 34 EXPLANATION Prints all lines containing the regular expression NW in a file called datafile . Example 4.6.% grep NW d* datafile: northwest NW Charles Main 3.0 .98 3 34 db: northwest NW Joel Craig 30 40 5 123 EXPLANATION Prints all lines containing the regular expression NW in all files starting with a d. The shell expands d* to all files that begin with a d . In this case, the filenames retrieved are db and datafile . Example 4.7.% grep '^n' datafile northwest NW Charles Main 3.0 .98 3 34 northeast NE AM Main Jr. 5.1 .94 3 13 north NO Margot Weber 4.5 .89 5 9 EXPLANATION Prints all lines beginning with an n . The caret (^) is the beginning-of-line anchor. Example 4.8.% grep '4$' datafile northwest NW Charles Main 3.0 .98 3 34 EXPLANATION Prints all lines ending with a 4 . The dollar sign ($) is the end-of-line anchor. Example 4.9.% grep TB Savage datafile grep: Savage: No such file or directory datafile: eastern EA TB Savage 4.4 .84 5 20 EXPLANATION Because the first argument is the pattern and all of the remaining arguments are filenames, grep will search for TB in a file called Savage and a file called datafile . To search for TB Savage, see the next example. Example 4.10.% grep 'TB Savage' datafile eastern EA TB Savage 4.4 .84 5 20 EXPLANATION Prints all lines containing the pattern TB Savage . Without quotes (in this example, either single or double quotes will do), the whitespace between TB and Savage would cause grep to search for TB in a file called Savage and a file called datafile , as in the previous example. Example 4.11.% grep '5\..' datafile western WE Sharon Gray 5.3 .97 5 23 southern SO Suan Chin 5.1 .95 4 15 northeast NE AM Main Jr. 5.1 .94 3 13 central CT Ann Stephens 5.7 .94 5 13 EXPLANATION Prints a line containing the number 5 , followed by a literal period and any single character. The "dot" metacharacter represents a single character, unless it is escaped with a backslash. When escaped, the character is no longer a special metacharacter, but represents itself, a literal period.
Example 4.12.% grep '\.5' datafile north NO Margot Weber 4.5 .89 5 9 EXPLANATION Prints any line containing the expression .5 . Example 4.13.% grep '^[we]' datafile western WE Sharon Gray 5.3 .97 5 23 eastern EA TB Savage 4.4 .84 5 20 EXPLANATION Prints lines beginning with either a w or an e . The caret (^) is the beginning-of-line anchor, and either one of the characters in the brackets will be matched. Example 4.14.% grep '[^0-9]' datafile northwest NW Charles Main 3.0 .98 3 34 western WE Sharon Gray 5.3 .97 5 23 southwest SW Lewis Dalsass 2.7 .8 2 18 southern SO Suan Chin 5.1 .95 4 15 southeast SE Patricia Hemenway 4.0 .7 4 17 eastern EA TB Savage 4.4 .84 5 20 northeast NE AM Main Jr. 5.1 .94 3 13 north NO Margot Weber 4.5 .89 5 9 central CT Ann Stephens 5.7 .94 5 13 EXPLANATION Prints all lines containing one nondigit. Because all lines have at least one nondigit, all lines are printed. (See the “v option in Table 4.2 on page 84.) Example 4.15.% grep '[A-Z][A-Z] [A-Z]' datafile eastern EA TB Savage 4.4 .84 5 20 northeast NE AM Main Jr. 5.1 .94 3 13 EXPLANATION Prints all lines containing two capital letters followed by a space and a capital letter; e.g., TB Savage and AM Main . Example 4.16.% grep 'ss* ' datafile northwest NW Charles Main 3.0 .98 3 34 southwest SW Lewis Dalsass 2.7 .8 2 18 EXPLANATION Prints all lines containing an s followed by zero or more consecutive occurrences of the letter s and a space. Finds Charles and Dalsass . Example 4.17.% grep '[a-z]\{9\}' datafile northwest NW Charles Main 3.0 .98 3 34 southwest SW Lewis Dalsass 2.7 .8 2 18 southeast SE Patricia Hemenway 4.0 .7 4 17 northeast NE AM Main Jr. 5.1 .94 3 13 EXPLANATION Prints all lines where there are at least nine consecutive lowercase letters, for example, northwest , southwest , southeast , and northeast . Example 4.18.% grep '\(3\)\.[0-9].* *' datafile northwest NW Charles Main 3.0 .98 3 34 EXPLANATION Prints the line if it contains a 3 followed by a period and another number, followed by any number of characters (.* ) , another 3 (originally tagged), any number of tabs, and another 3 . Because the 3 was enclosed in parentheses, \(3\) , it can be later referenced with \1. \1 means that this was the first expression to be tagged with the \( \) pair.
Example 4.19.% grep '\<north' datafile northwest NW Charles Main 3.0 .98 3 34 northeast NE AM Main Jr. 5.1 .94 3 13 north NO Margot Weber 4.5 .89 5 9 EXPLANATION Prints all lines containing a word starting with north . The \< is the beginning-of-word anchor. Example 4.20.% grep '\<north\>' datafile north NO Margot Weber 4.5 .89 5 9 EXPLANATION Prints the line if it contains the word north. The \< is the beginning-of-word anchor, and the \> is the end-of-word anchor. Example 4.21.% grep '\<[a-z].*n\>' datafile northwest NW Charles Main 3.0 .98 3 34 western WE Sharon Gray 5.3 .97 5 23 southern SO Suan Chin 5.1 .95 4 15 eastern EA TB Savage 4.4 .84 5 20 northeast NE AM Main Jr. 5.1 .94 3 13 central CT Ann Stephens 5.7 .94 5 13 EXPLANATION Prints all lines containing a word starting with a lowercase letter, followed by any number of characters, and a word ending in n . Watch the . * symbol. It means any character, including whitespace. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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