4.2. Variable Assignment
- =
the assignment operator (no space before and 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 4-2. Plain Variable Assignment
1 #!/bin/bash 2 # Naked variables 3 4 echo 5 6 # When is a variable "naked", i.e., lacking the '$' in front? 7 # When it is being assigned, rather than referenced. 8 9 # Assignment 10 a=879 11 echo "The value of \"a\" is $a." 12 13 # Assignment using 'let' 14 let a=16+5 15 echo "The value of \"a\" is now $a." 16 17 echo 18 19 # In a 'for' loop (really, a type of disguised assignment): 20 echo -n "Values of \"a\" in the loop are: " 21 for a in 7 8 9 11 22 do 23 echo -n "$a " 24 done 25 26 echo 27 echo 28 29 # In a 'read' statement (also a type of assignment): 30 echo -n "Enter \"a\" " 31 read a 32 echo "The value of \"a\" is now $a." 33 34 echo 35 36 exit 0
Example 4-3. Variable Assignment, plain and fancy
1 #!/bin/bash 2 3 a=23 # Simple case 4 echo $a 5 b=$a 6 echo $b 7 8 # Now, getting a little bit fancier (command substitution). 9 10 a=`echo Hello!` # Assigns result of 'echo' command to 'a' ... 11 echo $a 12 # Note that including an exclamation mark (!) within a 13 #+ command substitution construct will not work from the command-line, 14 #+ since this triggers the Bash "history mechanism." 15 # Inside a script, however, the history functions are disabled by default. 16 17 a=`ls -l` # Assigns result of 'ls -l' command to 'a' 18 echo $a # Unquoted, however, it removes tabs and newlines. 19 echo 20 echo "$a" # The quoted variable preserves whitespace. 21 # (See the chapter on "Quoting.") 22 23 exit 0
Variable assignment using the $(...) mechanism (a newer method than backquotes). This is likewise a form of command substitution.
1 # From /etc/rc.d/rc.local 2 R=$(cat /etc/redhat-release) 3 arch=$(uname -m)