On Wednesday 23 June 2010 02:24:51 littlebat wrote: > Hi, > I am learning LFS BOOK: > http://www.linuxfromscratch.org/lfs/view/6.6/chapter05/adjusting.html > > Below is a sed syntax I can't understand and haven't found a place to > learn it. > <code> > sed -e "/^\*cpp:$/{n;s,$, -isystem /tools/include,}" > </code>
Basically, '/^\*cpp:$/' is the address that matches lines that contain exactly '*cpp:'. The braces indicate a 'compound command'. 'n;s' means execute those two commands (n: print the pattern space; s: substitute the EOL with the 'option'). The effect is, as you know, to append the option to the end of all lines with just '*cpp:' on them. The commas are an unusual selection, but perfectly valid, since the s command allows pretty much any character to delimit the match and replace phrases. This could be rewritten as sed -e 's=^\(*cpp:\)=\1 -s system /tools/include/=' which would be a little more grokable. The only thing you need to find in the manual is the definition and use of the braces. Good enough? -- http://linuxfromscratch.org/mailman/listinfo/lfs-support FAQ: http://www.linuxfromscratch.org/lfs/faq.html Unsubscribe: See the above information page
