Process Management

Subshell Isolation

Changes Stay Inside

Parentheses run commands in a subshell. Variable changes inside the subshell do not overwrite the parent shell's variables.

Program

Play the script to compare the value inside a subshell with the value after it exits.

subshell_isolation.sh 
#!/usr/bin/env bash

start=
value=$start
(
    value=$((value + 10))
    echo "inside=$value"
)
echo "outside=$value"

#!/usr/bin/env bash

start=
value=$start
(
    value=$((value + 10))
    echo "inside=$value"
)
echo "outside=$value"

#!/usr/bin/env bash

start=
value=$start
(
    value=$((value + 10))
    echo "inside=$value"
)
echo "outside=$value"
subshell `( ... )` runs commands in a child shell process.
isolation Assignments inside the subshell do not change the parent shell.
parent value After the subshell finishes, the parent `value` is still the original value.