diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/grep.1 | 25 | ||||
| -rw-r--r-- | doc/grep.texi | 51 |
2 files changed, 49 insertions, 27 deletions
@@ -2,7 +2,7 @@ .de Id .ds Dt \\$4 .. -.Id $Id: grep.1,v 1.4 1999/08/13 14:45:14 alainm Exp $ +.Id $Id: grep.1,v 1.5 1999/10/06 01:12:44 alainm Exp $ .TH GREP 1 \*(Dt "GNU Project" .SH NAME grep, egrep, fgrep \- print lines matching a pattern @@ -61,10 +61,8 @@ and .B fgrep are available. .B Egrep -is similar (but not identical) to -.BR "grep\ \-E" , -and is compatible with the historical Unix -.BR egrep . +is the same as +.BR "grep\ \-E" . .B Fgrep is the same as .BR "grep\ \-F" . @@ -85,12 +83,12 @@ Print .I NUM lines of leading context before matching lines. .TP -.BI \-C " [NUM]" ", --context"[=NUM]" -Print +.BI \-C " [NUM]" ", --context" [=NUM] +Print .I NUM lines (default 2) of output context. .TP -.BI \- NUM \ +.BI \- NUM Same as --context=NUM lines of leading and trailing context. However, .B grep will never print any given line more than once. @@ -259,7 +257,8 @@ work correctly). Specifying overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of each line, this will cause some regular -expressions to fail. This option is only supported on MS-DOS and +expressions to fail. +This option has no effect on platforms other than MS-DOS and MS-Windows. .TP .B \-u, --unix-byte-offsets @@ -270,7 +269,8 @@ CR characters stripped off. This will produce results identical to running .B grep on a Unix machine. This option has no effect unless .B \-b -option is also used; it is only supported on MS-DOS and MS-Windows. +option is also used; +it has no effect on platforms other than MS-DOS and MS-Windows. .PD .SH "REGULAR EXPRESSIONS" .PP @@ -393,11 +393,6 @@ The preceding item is matched .I n or more times. .TP -.BI {, m } -The preceding item is optional and is matched at most -.I m -times. -.TP .BI { n , m } The preceding item is matched at least .I n diff --git a/doc/grep.texi b/doc/grep.texi index ff5cac41..557ea68d 100644 --- a/doc/grep.texi +++ b/doc/grep.texi @@ -377,7 +377,7 @@ Specifying @samp{-U} overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of each line, this will cause some regular -expressions to fail. This option is only supported on +expressions to fail. This option has no effect on platforms other than MS-DOS and MS-Windows. @item -u @@ -391,7 +391,7 @@ Report Unix-style byte offsets. This switch causes text file, i.e. the byte offsets ignore the CR characters which were stripped off. This will produce results identical to running @sc{grep} on a Unix machine. This option has no effect unless @samp{-b} -option is also used; it is only supported on MS-DOS and +option is also used; it has no effect on platforms other than MS-DOS and MS-Windows. @item -Z @@ -542,8 +542,7 @@ by newlines, any of which is to be matched. @end table In addition, two variant programs @sc{egrep} and @sc{fgrep} are available. -@sc{egrep} is similar (but not identical) to @samp{grep -E}, and -is compatible with the historical Unix @sc{egrep}. @sc{fgrep} is the +@sc{egrep} is the same as @samp{grep -E}. @sc{fgrep} is the same as @samp{grep -F}. @node Regular Expressions, Reporting Bugs, Grep Programs, Top @@ -705,12 +704,6 @@ The preceding item is matched exactly @var{n} times. @cindex match sub-expression n or more times The preceding item is matched n or more times. -@item @{,@var{m}@} -@opindex @{,m@} -@cindex braces, first argument omitted -@cindex match sub-expression at most m times -The preceding item is optional and is matched at most @var{m} times. - @item @{@var{n},@var{m}@} @opindex @{n,m@} @cindex braces, two arguments @@ -741,8 +734,42 @@ In basic regular expressions the metacharacters @samp{?}, @samp{+}, instead use the backslashed versions @samp{\?}, @samp{\+}, @samp{\@{}, @samp{\|}, @samp{\(}, and @samp{\)}. -In @sc{egrep} the metacharacter @samp{@{} loses its special meaning; -instead use @samp{\@{}. This not true for @samp{grep -E}. +@cindex interval specifications +There is a longstanding minor compatibility problem with regular +expressions like @samp{x@{2,8@}} that use interval specifications. +Traditional @command{egrep} did not support interval specifications, but +@sc{posix} requires them, and says that the effect of regular +expressions like @samp{x@{,8@}} or @samp{(@{2,8@})} is undefined because +their interval specifications are invalid. In @command{grep} 2.3 and +earlier, @samp{grep -E} acted as @sc{posix} required, but it reported an +error when it encountered a @samp{@{} that was not the prefix of a valid +interval specification. Had @command{egrep} 2.3 been equivalent to +@samp{grep -E}, it would have broken old-fashioned scripts that assume +that @samp{@{} is not special in egrep patterns. So @command{egrep} 2.3 +and earlier did not support interval specifications, even though +@sc{posix} required it. + +This compatibility problem has been addressed by changing @samp{grep -E} +to be less pedantic about invalid interval specifications. Instead of +reporting an error, @samp{grep -E} assumes that @samp{@{} is not special +if it would be the start of an invalid interval specification. For +example, @samp{grep -E @{1} now searches for the two-character string +@samp{@{1} instead of reporting a syntax error in the regular +expression. @sc{posix} allows this behavior as an extension, and it is +more compatible with what old-fashioned scripts expect of +@command{egrep}. + +The new behavior is incompatible with the traditional behavior in the +rare cases where @sc{posix} requires it. For example, @samp{egrep +x@{5@}} is now equivalent to @samp{egrep xxxxx} as required by +@sc{posix}, whereas it formerly was equivalent to @samp{egrep +'x\@{5\@}'}. Incompatibilities like these occur only when a valid +interval specification is found, not merely when @samp{@{} is found. + +This new behavior exists only to support old scripts that do not conform +to @sc{posix}. @sc{posix} does not define the behavior of invalid +interval specifications, and other @command{grep} implementations have +differing behavior in this area, so new scripts should avoid them. @node Reporting Bugs, Concept Index, Regular Expressions, Top |