Variable Assignment- =
the assignment operator (no space before &
after) | Do not confuse this with = and -eq, which test, rather than
assign! Note that = can be either an assignment
or a test operator, depending on context. |
Example 5-2. Plain Variable Assignment #!/bin/bash
# Naked variables
echo
# When is a variable "naked", i.e., lacking the '$' in front?
# When it is being assigned, rather than referenced.
# Assignment
a=879
echo "The value of \"a\" is $a."
# Assignment using 'let'
let a=16+5
echo "The value of \"a\" is now $a."
echo
# In a 'for' loop (really, a type of disguised assignment)
echo -n "Values of \"a\" in the loop are: "
for a in 7 8 9 11
do
echo -n "$a "
done
echo
echo
# In a 'read' statement (also a type of assignment)
echo -n "Enter \"a\" "
read a
echo "The value of \"a\" is now $a."
echo
exit 0 |
Example 5-3. Variable Assignment, plain and fancy #!/bin/bash
a=23 # Simple case
echo $a
b=$a
echo $b
# Now, getting a little bit fancier (command substitution).
a=`echo Hello!` # Assigns result of 'echo' command to 'a'
echo $a
# Note that using an exclamation mark (!) in command substitution
#+ will not work from the command line,
#+ since this triggers the Bash "history mechanism."
# Within a script, however, the history functions are disabled.
a=`ls -l` # Assigns result of 'ls -l' command to 'a'
echo $a # Unquoted, however, removes tabs and newlines.
echo
echo "$a" # The quoted variable preserves whitespace.
# (See the chapter on "Quoting.")
exit 0 |
Variable assignment using the $(...) mechanism
(a newer method than backquotes) # From /etc/rc.d/rc.local
R=$(cat /etc/redhat-release)
arch=$(uname -m) |
|
