On Sat, Aug 31, 2019 at 08:39:56AM -0400, The Wanderer wrote: > On 2019-08-31 at 07:58, Roberto C. Sánchez wrote: > > > On Sat, Aug 31, 2019 at 01:49:20PM +0200, Computer Planet wrote: > > > >> Hi guys! Is It possible, with "sed" erase all after a pattern? I'm > >> trying in all way but I can't... I'd like to erase all after the > >> pattern "config=" but only in the same line, regardless of where it > >> is located inside in a file. > >> > >> Can somebody help me please? Thank in advance for reply. > >> > >> e.g.: after "config=" erase all until the end of the line > > > > Something like this: > > > > sed -E 's/(.*config=).*/\1/' > > Or perhaps > > sed 's/config=.*$/config=/g' > > ? > > Less elegant and idiomatic, but could also get the job done. > OK.
> The 'g' at the end is in case there can be multiple occurrences of > 'config=' in a single file, so that sed won't stop after the first one > it finds. > That's not how 'g' works. It is global replace of all occurences of the patter in the pattern space. By default, sed operates one line at a time so the replacement will happen on every line that matches the pattern even without the 'g'. $ cat ~/test.txt Test config=foo Test config=foo Test config=foo $ sed 's/config=.*$/config=/g' ~/test.txt Test config= Test config= Test config= $ sed 's/config=.*$/config=/' ~/test.txt Test config= Test config= Test config= Since the desired effect is "replace everything to the end of the line" then the 'g' has no practical effect. It is not really possible to have multiple patterns match to the end of the line, unless you were trying to do some form of relucant matching. > > In practice, I'd either use this with 'sed -i [the above expression] > filename' or (more likely) with 'cat filename | sed [the above > expression] > newfilename'. > > (Yes, that's technically a "senseless use of cat". I do it anyway, > because always using pipes at every stage makes it easy to add or remove > filtering stages without having to adjust the syntax in another part of > the pipeline, and because it's easier to stick with that habitual > pattern than to change it up in the relatively few cases where I can be > sure that multiple stages aren't and won't be needed.) > > (And may I say that it's annoying to need to explain this every time, in > order to forestall being called out for "senseless use of cat"? Not that > I get called out for that here very much, but it does seem to happen > virtually every time I don't include an explanation...) > You can avoid cat with something like this: sed [expr] filename > newfilename To add more sed expressions: sed -e [expr1] -e [expr2] filename > newfilename To add something after sed: sed -e [expr1] -e [expr2] filename | othercmd > newfilename The only time you need to change the syntax is to add something before sed. But then, that's why shells have I/O redirection: (sed 's/config=.*$/config=/g' | tr -d '=') <~/test.txt >~/other_test.txt $ cat ~/other_test.txt Test config Test config Test config Now I can add pipe stages within the sub-shell to my hearts content and I can even do other things like replace "<~/test.txt" with "<$(some other command that queries a database)" so that the input does not even need to come from a real file. Regards, -Roberto -- Roberto C. Sánchez
