Linux declare Command
Linux Command EncyclopediaThe Linux declare command is used to declare shell variables.
declare is a shell command. In the first syntax, it can be used to declare variables and set variable attributes ([rix] refers to the variable attributes). In the second syntax, it can be used to display shell functions. If no parameters are added, all shell variables and functions will be displayed (the same effect as executing the set command).
Syntax
declare [+/-][rxi][变量名称＝设置值] 或 declare -f
Parameter Description：
- +/- "-" can be used to specify variable attributes, while "+" cancels the attributes set for the variable.
- -f Only displays functions.
- r Sets the variable to read-only.
- x The specified variable becomes an environment variable, available for use by programs outside the shell.
- i [Setting value] can be a numeric value, string, or expression.
Examples
Declaring an integer variable
Example
# declare -i ab //Declare an integer variable
# ab=56 //Change the variable content
# echo $ab //Display the variable content
56
# ab=56 //Change the variable content
# echo $ab //Display the variable content
56
Changing variable attributes
Example
# declare -i ef //Declare an integer variable
# ef=1 //Variable assignment (integer value)
# echo $ef //Display the variable content
1
# ef="wer" //Variable assignment (text value)
# echo $ef
0
# declare +i ef //Cancel the variable attribute
# ef="wer"
# echo $ef
wer
# ef=1 //Variable assignment (integer value)
# echo $ef //Display the variable content
1
# ef="wer" //Variable assignment (text value)
# echo $ef
0
# declare +i ef //Cancel the variable attribute
# ef="wer"
# echo $ef
wer
Setting a variable to read-only
Example
# declare -r ab //Set the variable to read-only
# ab=88 //Change the variable content
-bash: ab: read-only variable
# echo $ab //Display the variable content
56
# ab=88 //Change the variable content
-bash: ab: read-only variable
# echo $ab //Display the variable content
56
Declaring an array variable
Example
# declare -a cd='(
# echo ${cd[1]}
b //Displaying the variable content
# echo ${cd[@]} //Display the entire array variable content
a b c
# echo ${cd[1]}
b //Displaying the variable content
# echo ${cd[@]} //Display the entire array variable content
a b c
Displaying functions
Example
# declare -f
command_not_found_handle ()
{
if [ -x /usr/lib/command-not-found ]; then
/usr/bin/python /usr/lib/command-not-found -- $1;
return $?;
else
if [ -x /usr/share/command-not-found ]; then
/usr/bin/python /usr/share/command-not-found -- $1;
return $?;
else
return 127;
fi;
fi
}
command_not_found_handle ()
{
if [ -x /usr/lib/command-not-found ]; then
/usr/bin/python /usr/lib/command-not-found -- $1;
return $?;
else
if [ -x /usr/share/command-not-found ]; then
/usr/bin/python /usr/share/command-not-found -- $1;
return $?;
else
return 127;
fi;
fi
}