Variable Assignment in Shell Scripting
How assignment Operator works in Shell scripting?
=
the assignment operator (no space before and after)
Caution
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: 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: 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 including an exclamation mark (!) within a
#+ command substitution construct #+ will not work from the command line,
#+ since this triggers the Bash "history mechanism."
# Inside 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 $(...) mechanism (a newer method than backquotes). This is actually a form of command substitution.
# From /etc/rc.d/rc.local
R=$(cat /etc/redhat-release)
arch=$(uname -m)
