When debugging a Bash script that exits unexpectedly due to set -e, you need to identify which command caused the exit. Here’s a step-by-step approach:

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1. Understand set -e Behavior

• set -e makes the script exit immediately if any command returns a non-zero status (i.e., fails).
• The script exits at the first failing command after set -e is enabled.

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2. Debugging Methods

A. Add set -x for Tracing

• Insert set -x at the top of your script (or before the suspicious section).
• This prints each command and its arguments as they are executed, along with the exit status of each command.
• Look for the last command printed before the script exits. Its non-zero exit status is the culprit.

Example:

bash
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#!/bin/bash
set -e
set -x  # Enable tracing

# Your commands here
command1
command2
command3

B. Use trap to Catch Errors

• Add a trap to print the failing command and its line number when the script exits due to set -e.

Example:

bash
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#!/bin/bash
set -e

trap 'echo "Script failed at line $LINENO. Last command: $BASH_COMMAND"' ERR

# Your commands here
command1
command2
command3

• When the script exits, it will print the line number and the last command that failed.

C. Check Exit Status Manually

• Temporarily disable set -e and add manual checks for each command’s exit status.

Example:

bash
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#!/bin/bash
# set -e  # Comment out for debugging

command1 || { echo "command1 failed with status $?"; exit 1; }
command2 || { echo "command2 failed with status $?"; exit 1; }
command3 || { echo "command3 failed with status $?"; exit 1; }

D. Use bash -x or bash -v

• Run your script with bash -x script.sh to trace execution.
• Or use bash -v script.sh to print each line as it is read.

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3. Common Pitfalls

• Commands in Pipelines: By default, set -e does not fail on pipeline failures. Use set -o pipefail to ensure pipelines fail if any command in the pipeline fails.
• Conditional Statements: Commands in if, while, etc., do not trigger set -e exits.
• Functions: If a function fails, the script exits only if the function is called in a context where set -e applies.

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4. Example Workflow

1. Add set -x and trap to your script.
2. Run the script and observe the output.
3. Identify the last command printed before the exit.
4. Check the exit status of that command using echo $? or the trap output.

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Question: Do you have a specific script or section you’d like help debugging? If so, share it and I can help pinpoint the issue!