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Diffstat (limited to 'doc/grep.texi')
-rw-r--r-- | doc/grep.texi | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/doc/grep.texi b/doc/grep.texi index 78efb189..de73d7f0 100644 --- a/doc/grep.texi +++ b/doc/grep.texi @@ -50,7 +50,7 @@ Texts. A copy of the license is included in the section entitled @node Top @top grep -@command{grep} prints lines that match a pattern. +@command{grep} prints lines that contain a match for a pattern. This manual is for version @value{VERSION} of GNU Grep. @@ -1170,6 +1170,7 @@ The preceding item is matched at least @var{n} times, but not more than @end table +The empty regular expression matches the empty string. Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings @@ -1629,6 +1630,19 @@ grep 'paul' /etc/motd | grep 'franc,ois' finds all lines that contain both @samp{paul} and @samp{franc,ois}. @item +Why does the empty pattern match every input line? + +The @command{grep} command searches for lines that contain strings +that match a pattern. Every line contains the empty string, so an +empty pattern causes @command{grep} to find a match on each line. It +is not the only such pattern: @samp{^}, @samp{$}, @samp{.*}, and many +other patterns cause @command{grep} to match every line. + +To match empty lines, use the pattern @samp{^$}. To match blank +lines, use the pattern @samp{^[[:blank:]]*$}. To match no lines at +all, use the command @samp{grep -f /dev/null}. + +@item How can I search in both standard input and in files? Use the special file name @samp{-}: |