March 08, 2021
set -euo pipefail
# Abort script if command returns with non-zero exit code
set -e
set -o errexit
# Abort script if variable is dereference when it has not been set
# This prevents unbound variables from ever being used.
set -u
set -o nounset
# Prevents errors in pipeline from being masked
# Pipeline return code is that of last command
set -o pipefail
Some recommend that scripts be run with set -euo pipefail right below the shebang line
Trap
We can also use trap function ERR to act as a catch.
#!/bin/bash
echo "hello"
err_report() {
echo "exit on line $(caller)"
}
trap err_report ERR
echo hello | grep foo
echo "This line will still be printed"
Trap allows you to handle the error in a function. However, it will not exit on 1 by default. You can add a exit 1 in the err_report function.
Also, another caveat is, trap does not work if the error is thrown in a function that is called within a function that is not the return value:
outer_fun() {
err_fun
echo hello
}
outer_fun
This is because the outer scope only cares about the return value of a function which is the last line of the function.
Hence it is good practice to use set -eu in conjunction with trap function ERR in order to have a well rounded, holistic solution. Where all errors are caught and program exits.
Trapping others
Apart from ERR, you can also trap other signals like EXIT, SIGINT, SIGTERM and KILL.
Note:
echo hello | grep foo; echo $?Returns the exit code.- grep returns 0 when there is a match
- grep returns 1 when there is no match
References