On 21/05/03 04:28PM, Greg Reagle wrote: > Would sbase suck less if the program head, which is currently a C program of > 77 lines, were replaced with something like > #!/bin/sh > sed "$1"q > > I know that it would need to be a bit more elaborate than that to handle the > -n flag, but still. Is there any advantage to having a separate C program? >
It's for performance or/and convenience reasons. It could be a shell script. head is a utility as defined by POSIX https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_22 A utility can be a shell script and there shouldn't be a difference in behavior. I think it's easier to write and maintain a POSIX compliant head when it's written in C, because it has to handle -n option and multiple files with a special output header. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/head.html The head is more for convenience too. In RATIONALE: > Although it is possible to simulate head with sed 10q for a single > file, the standard developers decided that the popularity of head on > historical BSD systems warranted its inclusion alongside tail. >From https://en.wikipedia.org/wiki/Head_(Unix)#Other: > Many early versions of Unix did not have this command, and > documentation and books used sed instead: You could write POSIX compliant head in POSIX compliant shell and it would be correct. Of course if you don't need to be POSIX compliant you could drop head altogether. I would say most people write these tools in C for performance reasons. For example look at GNU cat code. Regards, mat
