On Thu, Sep 28, 2006 at 09:12:47PM +0600, [EMAIL PROTECTED] wrote: [...] > Description: > When Process substitution is used, BASH > reads from such descriptor by one bytes!!
Of course it does. A shell is a shell, it's a command that runs other commands. read var Reads one line of input (potentially more without -r). You don't want it to read more than one line of input, because you want the next command to be able to read the next line. And the only way to make sure that only one line is read and not more is to read one character at a time until the LF character is found. For regular files, shells like bash or ksh do some optimisations, they read a buffer worth of data, and then, in case another command is to be run, they seek back (move the "read" cursor position if you prefer) to the character after the LF. This kind of thing can't be done with a pipe of course, you can't tell the process at the other end "please restart from that newline character". It can only be done with regular files (not with devices, sockets, pipes...). So, it's a perfectly normal behavior. That's rather the optimisation that is not normal (in the sense that it reads more than what you may expect it to). > Repeat-By: > -------------------------- > /tmp/test: > --begin-- > #!/bin/bash > while read line; do > qwe=qwe > done < <( cat /etc/passwd ) > --end-- > chmod +x /tmp/test > strace /tmp/test > -------------------------------------- > You'll see that BASH read bytes from pipe one-by-one. > Another script will not trigger this problem: > #!/bin/bash > while read line; do > qwe=qwe > done < /etc/passwd [...] -- Stephane _______________________________________________ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
