STDIN and STDOUT

UNIX for Beginners Q & A UNIX for Dummies Questions & Answers
1

Hallo,

i have a script like:

if [$1] ;then
echo "OK"

else 
echo "ERROR $2 is missing"

fi;

if [$2];then
touch $2

fi;

if [$2];then
 cat $1  | grep xy > $2

fi;

but i must do that with STDIN and STDOUT, when i want to run the script it must not give parameters. It must run like

cat zz | ./rrr.sh > zz_solution.txt
2

There's an awful lot of useless use of cat in your scripts. The reason why cat is useless here also explains what you should be doing in your script instead: just use redirection. Or just leave things unchanged so other things can do redirection.

grep xy < zz > zz_solution.txt

If you insisted on putting it in a script, which seems unnecessary when it's only one line, you'd just do:

#!/bin/sh
grep xy

Without parameters, grep will read from stdin and print to stdout, and you can redirect it from the outside.