/[grep]/grep/doc/grep.texi
ViewVC logotype

Diff of /grep/doc/grep.texi

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 1.56 by charles_levert, Wed Aug 24 07:28:29 2005 UTC revision 1.57 by julianfoad, Tue Nov 8 19:45:05 2005 UTC
# Line 1251  Note this is done by using GNU ERE exten Line 1251  Note this is done by using GNU ERE exten
1251  other greps.  other greps.
1252    
1253  @item  @item
1254  Why are my expressions whith the vertical bar fail?  Why is this back-reference failing?
1255    
1256  @example  @example
1257  /bin/echo "ba" | egrep '(a)\1|(b)\1'  echo 'ba' | egrep '(a)\1|b\1'
1258  @end example  @end example
1259    
1260  The first alternate branch fails then the first group was not in the match  This gives no output, because the first alternate @samp{(a)\1} does not match,
1261  this will make the second alternate branch fails.  For example, "aaba" will  as there is no @samp{aa} in the input, so the @samp{\1} in the second alternate
1262  match, the first group participate in the match and can be reuse in the  has nothing to refer back to, meaning it will never match anything.  (The
1263  second branch.  second alternate in this example can only match if the first alternate has
1264    matched -- making the second one superfluous.)
1265    
1266  @item  @item
1267  What do @command{grep, fgrep, egrep} stand for ?  What do @command{grep, fgrep, egrep} stand for?
1268    
1269  grep comes from the way line editing was done on Unix.  For example,  The name @command{grep} comes from the way line editing was done on Unix.  For
1270  @command{ed} uses this syntax to print a list of matching lines on the screen.  example, @command{ed} uses the following syntax to print a list of matching
1271    lines on the screen:
1272    
1273  @example  @example
1274  global/regular expression/print  global/regular expression/print

Legend:
Removed from v.1.56  
changed lines
  Added in v.1.57

savannah-hackers-public@gnu.org
ViewVC Help
Powered by ViewVC 1.1.26