What does this command do?

grep "\bi\b" linux.txt

What is it searching for?

  • It may be obvious, but just in case it is not, here is a note on the (significant) difference between \<...\> and \b...\b: `You can get unexpected results if you assume the two patterns behave the same... see this link – Peter.O Oct 16 '11 at 18:23

\b in a regular expression means "word boundary".

With this grep command, you are searching for all words i in the file linux.txt. i can be at the beginning of a line or at the end, or between two space characters in a sentence.

  • can be in the begining or in the end?? isn't supposed to be only between spaces?? – amyassin Oct 16 '11 at 19:43
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    I don't find more details about that. But trying by hand with a file containing the lines "i foo" and "bar i", the regexp provided to the grep command above is matching both of them. – uloBasEI Oct 16 '11 at 19:53
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    More precisely, not only space, but any non-word character. Just like the -w --word-regexp switch does: grep -w "i" linux.txt. For example a line like "<i>italic</i>" also matches. – manatwork Oct 17 '11 at 6:48

The \b (word boundary) anchor can be used in place of \< and \> to signify the beginning or end of a word.

If this is the content of a file:

is test file
to carry out few regular expressions


$ grep -e '\breg' file
to carry out few regular expressions

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