ned@SCINEWS.UUCP (Ned Robie) (03/30/85)
Does anyone know what the undocumented <> io redirection metacharacter sequence in the bourne shell does? Is it useful? -- Ned Robie, SCI Systems, RTP
mike@enmasse.UUCP (Mike Schloss) (04/04/85)
> Does anyone know what the undocumented <> io redirection metacharacter > sequence in the bourne shell does? Is it useful? What it does: redirects input from specified file but open() is called for read/write instead of read only Is it useful: Doubtful Mike Schloss
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (04/06/85)
> Does anyone know what the undocumented <> io redirection metacharacter > sequence in the bourne shell does? It opens the subsequently-named file in mode 2 (read+write). > Is it useful? I've never found a reason to use it.
lcc.richard@UCLA-LOCUS.ARPA (Richard Mathews) (04/24/85)
> > Does anyone know what the undocumented <> io redirection metacharacter > > sequence in the bourne shell does? Is it useful? > > What it does: > redirects input from specified file but open() is called > for read/write instead of read only > > Is it useful: > Doubtful Well, I managed to find a use for it. It turns out that "more" tries to READ STDERR! (yucch!), so I wanted to open stderr for read/write. I discovered why this "feature" is undocumented. It does not work. I tried it on the Sys V.2, BSD 4.1, and BSD 4.2 Bourne shells. On all of these it only opened the file for read. I took a look at the shell source. When it sees this construct, it sets a bit, IORDW, in its I/O structure. Unfortunately, this bit never gets tested. When the shell goes to open the file, it will just end up falling into the code it uses for ">filename". As I side issue, if "more" cannot read stderr for any reason other than EINTR, it exits WITHOUT SETTING THE TERMINAL MODES BACK! Richard M. Mathews Locus Computing Corporation lcc!richard@ucla-cs {ucivax,trwrb}!lcc!richard {ihnp4,randvax,sdcrdcf,ucbvax,trwspp}!ucla-cs!lcc!richard