The pipefail option is inconspicuous but very important.

set -o pipefailIt is a commonly used command in Bash shell scripts. Its function is to change the exit status of pipeline commands.

By default, the exit status of a pipeline command (a command composed of multiple commands connected by the pipe symbol |) is the exit status of the last command, regardless of whether the previous command was executed successfully.

For example, the following command:

command1 | command2

If command1 fails (returns a non-zero exit status), but command2 succeeds (returns a zero exit status), then the exit status of the entire pipeline command is 0 (success).

But if you use it set -o pipefail, then if command1 fails, the exit status of the entire pipeline command will be the exit status of command1, even if command2 succeeds.

This option is typically used for error handling, ensuring that every command in the pipeline executes successfully. If any one command in the pipeline fails, the entire pipeline command is considered failed, so the error can be caught in the script and handled accordingly.

Here's an example.

Suppose we have two commands, command1 and command2. command1 always fails, command2 always succeeds. We can simulate this situation with a simple script:

#!/bin/bash

# 定义一个总是失败的命令
command1() {
    
    
  echo "Running command1"
  return 1
}

# 定义一个总是成功的命令
command2() {
    
    
  echo "Running command2"
  return 0
}

# 不使用 set -o pipefail
echo "Without set -o pipefail"
command1 | command2
echo "Exit status: $?"

# 使用 set -o pipefail
echo "With set -o pipefail"
set -o pipefail
command1 | command2
echo "Exit status: $?"

output

Without set -o pipefail
Running command2
Exit status: 0
With set -o pipefail
Running command2
Exit status: 1

In this script, command1 and command2 are both functions that return 1 (failure) and 0 (success) respectively.
When we don't use it set -o pipefail, even though command1 failed, the exit status of the entire pipeline command is still 0 because command2 succeeded.
When we use set -o pipefail, although command2 succeeds, the exit status of the entire pipeline command is 1 because command1 failed.

summary

It’s a small basic that can make a huge difference when we master it and use it correctly.

Just like a brick, we can use it to build a chicken coop, a pigsty, or a building.

Practice the basic skills hard and encourage each other.