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Grep Count

Grep Count

Philip Wilkinson
Philip Wilkinson
Software Engineer, Amazon

While [.inline-code]grep[.inline-code] is most often used for finding strings and neighboring text, it can be used for counting lines and occurrences as well.

[#count-lines][.inline-code]grep[.inline-code] count lines[#count-lines]

To count the number of lines that a string appears in using [.inline-code]grep[.inline-code]:

 $ grep -c “string” 

For which the [.inline-code]-c[.inline-code] flag is used to count the number of lines that are matched and print out the number. This can be useful, for example, when you want to search through log files for the number of entries from a particular IP, endpoint or other identifier where you only care about the number of lines, not the full number of matches.

[#count-occurrences][.inline-code]grep[.inline-code] count occurrences[#count-occurrences]

If however you want to count the number of occurrences of a string, beyond simply the number of lines, then the command can be used:

 $ grep -o  “string”   | wc -l

For which, the [.inline-code]-o[.inline-code] flag gets the occurrence of that string, while [.inline-code]wc -l[.inline-code] will count the number of times the occurrence appears on each line. This is useful when you want to know how many times a particular string occurs in a document such as the number of times a name, variable or IP address appears.

[#print-occurrences][.inline-code]grep[.inline-code] print occurrences[#print-occurrences]

This command is simplified if you only want to print out the occurrences of that string rather than count the number of occurrences. This is done using:

 $ grep -o  “string” 

For which the [.inline-code]-o[.inline-code] flag is used to print out the matches on each line. This is useful when you want to see the context of the matches in the text they are part of, such as what strings the matches end up as. 

[#common-gotchas]Common “gotchas” when using [.inline-code]grep[.inline-code] to count[#common-gotchas]

[#using-regex][.inline-code]grep[.inline-code] uses regex standards[#using-regex]

It is important to know that the “string” following the [.inline-code]grep[.inline-code] command will match the document based on regular expression standards. This means that simply typing in [.inline-code]test[.inline-code] will match on longer strings containing that word such as “testing”. To match only the specific word use regex expressions or the [.inline-code]-w[.inline-code] flag. For example:

 $ grep -o “\btest\b”  |wc -l
 $ grep -ow “test”  | wc -l

[#multiple-words][.inline-code]grep[.inline-code] counting multiple words[#multiple-words]

 $ grep -o -E “string1|string2”  | sort | uniq -c

If you want to search for multiple words at the same time, this command becomes more complicated. To print out the word and count you can use:

Read more on grep multiple strings to understand how the “or” part of this command came together.

[#counting-across-multiple-files][.inline-code]grep[.inline-code] counting across multiple files[#counting-across-multiple-files]

To match across multiple files and count the occurrences then this can become even more complicated. But the following command should print out the occurrences and which file they occur in:

 $ grep -0 “string”   | cut -d ‘:’ -f 1 | uniq -c

All of these commands can also be combined with the [.inline-code]-i[.inline-code] flag so that the string match is case insensitive

[#using-awk-or-sed]Use [.inline-code]awk[.inline-code] or [.inline-code]sed[.inline-code] for text manipulation[#using-awk-or-sed]

If you want to manipulate text, or work with specific fields of a file, you will probably want to use a more specific tool such as [.inline-code]sed[.inline-code] or [.inline-code]awk[.inline-code]

[#learn-more]Find out more about [.inline-code]grep[.inline-code][#learn-more]

As always if you want to find out more about how to use the grep tool you can use:

 $ man grep

Which will print out all the options with explanations. Or:

 $ grep --help

Which will print out a short page of all the available options.

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