I wrote: > Could someone tell me why the following works in zsh but not in > bash/posh/dash? > > benjo[3]:~% echo foo bar baz | read a b c > benjo[4]:~% echo $a $b $c > foo bar baz
Thanks everyone for the enlightening answers! So just to summarize, the problem is that the pipeline is treated as a subshell, and so the variables $a $b and $c are defined within the subshell but not the "main" shell. These seem like the best solutions to my problem: * Bash-specific (i.e. not POSIX-compliant) : David Kirchner wrote: > I'm not sure of the POSIX way to use read in this manner, but I found > this on Google/A9: > > http://linuxgazette.net/issue57/tag/1.html > > The example he gives, with the < <() syntax, worked in bash, but not > in Debian or FreeBSD's /bin/sh. Almut Behrens wrote: > In more recent bashes, the following should work as well > > #!/bin/bash > read a b c <<<`echo foo bar baz` > echo $a $b $c > > The <<< ("here strings") are an extension of the "here document" syntax, > IOW, the string given after <<< is supplied as stdin to the command. * POSIX-compliant: Bill Marcum wrote: > I think the POSIX way would be > echo foo bar baz | { read a b c; echo $a $b $c; } Not too bad if what you want to do inside the { } braces is pretty short. Almut Behrens wrote: > #!/bin/sh > eval `echo foo bar baz | (read a b c; echo "a='$a';b='$b';c='$c'" )` > echo $a $b $c > > To get the variable's values from the subshell back to the main shell, > a shell code fragment is written on stdout, captured with backticks, > and then eval'ed in the main shell... (this is the moment when I > usually switch to some other scripting language -- if not before :) Ugh. Does get the job done though. I guess one has to be a little careful about escaping special characters in this case? Here's the safest version I've found so far -- single quotes in the input have to be special cased with the sed command, and the -r flag to "read" keeps it from eating backslashes. # set some variables to nightmarish values for testing purposes d='"ab\""q"' # literal value is "ab\""q" e='$d' # literal value is $d f="'ba'r'" # literal value is 'ba'r' # here's the meat of the code result="`echo "$d $e $f" | sed "s/'/\'\\\\\\\'\'/g" | \ ( read -r a b c; echo "a='$a' ; b='$b' ; c='$c'" )`" eval "$result" # test that $a $b $c have the right values echo "$a $b $c" Tested on Sarge with zsh, bash, dash and posh :-) Of course, replace this: echo "$d $e $f" with whatever is producing the output that needs to be put into $a $b $c Personally, I'd rather constrain my script to work only with bash and use <<< or < <() operators than to write something like the above! (N.B. every method above still needs the -r flag to read if the input might contain backslashes.) best regards, -- Kevin B. McCarty <[EMAIL PROTECTED]> Physics Department WWW: http://www.princeton.edu/~kmccarty/ Princeton University GPG: public key ID 4F83C751 Princeton, NJ 08544 -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
