Grep

From NovaOrdis Knowledge Base
Revision as of 03:01, 16 February 2016 by Ovidiu (talk | contribs)
Jump to navigation Jump to search

Internal

Overview

grep accepts regular expressions. Both " " and ' ' can be used to enclose the expression to search for.

If the expression is found, the enclosing lines are sent to stdout the command returns 0 (success).

If the expression is NOT found, the command returns 1 (failure).


    if grep -q "some regex" ./file.txt; then
        # do something if expression is found
    else
        # do something else if the expression is not found
    fi

Regular Expressions

^ - beginning of line

$ - end of line

\t - tab

[0-9]*

\. dot

!!!Including TWO expressions at the same time

grep 'processor\

The method works even if there are spaces and other regular expression characters within the alternative regexes:

grep ' logger: [1-9]\+\.\

This will select either "logger: [[1-9]\+\." or "(concurrent mode failure)"


!!!Excluding TWO expressions at the same time

grep -v "blah" 

!!!Do not Send Anything to stout

... and avoid > /dev/null:

{{{

   grep -q

}}}


!!!--color

{{{ grep --color 'context.layer=' }}}

!!!-n

Prefixes the line with the line number.


See [sed#InsertALineAppendInASpecificPositionLineNumberInAFile]

!!!Characters that Need Escaping

Same as [sed#SpecialCharactersNeedToBeEscapedInRegularExpressions]


!!!Return Only the First Match

{{{ -m 1 }}}



__Referenced by:__\\ [{INSERT com.ecyrd.jspwiki.plugin.ReferringPagesPlugin WHERE max=20, maxwidth=50}]