-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 According to Bas van Gompel on 1/24/2006 10:11 PM: > Hi, > > Try the following script: > > === begin testexec.sh === > #!/bin/ksh > > exec 5<&0 /bin/ksh <<EOSH > echo "First exec: Done." > exec 0<&5 > echo "Second exec: Done." > exit 0 > EOSH > ==== end testexec.sh ====
First line: This could be rewritten "exec /bin/ksh 5<&0 <<EOSH". Either way, you are replacing the current shell with an invocation of /bin/ksh, and with fd 5 set to your current stdin, and then with fd 0 set to a pipe supplied by the contents of the here-doc. Now ksh gets through the following input on stdin: echo "First exec: Done." exec 0<&5 At which point, the second exec says take fd 5 and dup it into fd 0 (in other words, restore your original stdin from before the first exec back to ksh's stdin). POSIX requires that ksh reads its input from stdin a line at a time, so the very next line it reads will be whatever you type (if the original stdin happened to be a terminal). Only ash is buggy here (no big surprise, ash is usually the least POSIX-compliant of the shells); ksh, zsh, and bash are all doing what is required of them. > > (Replace ksh with bash or zsh at will, above.) > > For me, this prints ``First exec: Done.'', then leaves me to type > shell-commands, _which are executed_, until I press EOF (^D). > > In ash it prints '' > > First exec: Done. > Second exec: Done. > > '', as I expected. Compare p.e. Your expectation was wrong. > > === begin testexec2.sh === > #!/bin/bash > > echo 'echo "First exec: Done." > exec 0<&5 > echo "Second exec: Done." > exit 0' |exec 5<&0 /bin/bash > > ==== end testexec2.sh ==== Here, you are doing something slightly different. The last line is a pipeline, which must be applied before redirections. Which means that you are exec'ing /bin/bash, with fd 0 set to the pipeline from the echo, then fd 5 copied from fd 0. When the second "exec 0<&5" is reached, you copy fd 5 back to fd 0, but since it was the same fd, it was effectively a no-op. Therefore, /bin/bash continues to read the next line from fd 0, and successfully prints "Second exec: Done." > > , which also performs as expected. > > Has anybody got a clue? > > Is this cygwin-specific? No. > > Are all these shells borrowing code from eachother? No. - -- Life is short - so eat dessert first! Eric Blake [EMAIL PROTECTED] volunteer cygwin bash maintainer -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org iD8DBQFD144p84KuGfSFAYARAk9wAKCsfgwDH6yg/TVIqprI7mhpnfQxxgCgvpi+ JkYBe7wXat74LuBY6fedRvI= =JX9+ -----END PGP SIGNATURE----- -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
