badread.sh

Shall高级编程

#!/bin/bash
#  badread.sh:
#  Attempting to use 'echo and 'read'
#+ to assign variables non-interactively.

a=aaa
b=bbb
c=ccc

echo "one two three" | read a b c
# Try to reassign a, b, and c.

echo
echo "a = $a"  # a = aaa
echo "b = $b"  # b = bbb
echo "c = $c"  # c = ccc
# Reassignment failed.

# ------------------------------

# Try the following alternative.

var=`echo "one two three"`
set -- $var
a=$1; b=$2; c=$3

echo "-------"
echo "a = $a"  # a = one
echo "b = $b"  # b = two
echo "c = $c"  # c = three 
# Reassignment succeeded.

# ------------------------------

#  Note also that an echo to a 'read' works within a subshell.
#  However, the value of the variable changes *only* within the subshell.

a=aaa          # Starting all over again.
b=bbb
c=ccc

echo; echo
echo "one two three" | ( read a b c;
echo "Inside subshell: "; echo "a = $a"; echo "b = $b"; echo "c = $c" )
# a = one
# b = two
# c = three
echo "-----------------"
echo "Outside subshell: "
echo "a = $a"  # a = aaa
echo "b = $b"  # b = bbb
echo "c = $c"  # c = ccc
echo

exit 0