Many Linux administrators encounter this frustrating error when processing user data from CSV files:

./test.sh: line 5: UID: readonly variable

The script might work perfectly in development but fails in production environments. Let's examine why this happens and how to properly handle system-reserved variables.

The error occurs because UID is a special shell variable in Unix/Linux systems. It's a readonly variable that stores the current user's numeric ID. When your script tries to reassign it, the shell prevents modification.

Here's the corrected version of the script with proper variable naming:

#!/bin/bash

while IFS= read -r inputline
do
    user_id="$(echo "$inputline" | cut -d '\"' -f4)"
    password="$(echo "$inputline" | cut -d '\"' -f8)"
    first_name="$(echo "$inputline" | cut -d '\"' -f6 | cut -d ' ' -f1)"
    last_name="$(echo "$inputline" | cut -d '\"' -f6 | cut -d ' ' -f2)"    
    
    zmprov createAccount "$user_id" "$password" displayName "$first_name $last_name" \
        givenName "$first_name" sn "$last_name"
    
done < company.csv

• Changed UID to user_id to avoid system variable conflict
• Added -r to read to preserve backslashes
• Set IFS= to prevent leading/trailing whitespace trimming
• Quoted all variable expansions to handle spaces/special characters
• Used #!/bin/bash shebang for more consistent behavior

For more robust CSV parsing, consider these approaches:

# Using awk for better field handling
user_id=$(awk -F'"' '{print $4}' <<< "$inputline")

# Using IFS for direct field splitting
IFS=\" read -r _ _ _ user_id _ _ _ password _ first_last _ <<< "$inputline"

You can list all read-only shell variables with:

readonly -p | grep -E '^declare -r'

Common reserved variables to avoid include: UID, EUID, PPID, SHELLOPTS, and BASH_VERSINFO.

When migrating scripts between environments:

1. Test with bash -n script.sh for syntax errors
2. Run shellcheck script.sh for common pitfalls
3. Consider using environment-specific variable prefixes
4. Implement proper error handling and logging

When working with bash scripts that handle user account creation or data processing, you might encounter the frustrating "readonly variable" error for UID. This typically occurs when:

• Running scripts across different Linux environments
• Processing CSV files containing user information
• Attempting to modify system-reserved variables

The error occurs because UID is a special shell variable in Unix-like systems (declared readonly in POSIX) that stores the current user's numeric ID. When your script tries to assign a new value to it, the shell prevents modification.

# Try this in your terminal:
echo $UID  # Shows your current user ID
UID=1001   # Will produce "UID: readonly variable"

Here are three robust approaches to handle this:

# Option 1: Use a different variable name (recommended)
user_id="$(echo $inputline | cut -d '\"' -f4)"

# Option 2: Use lowercase (convention for script variables)
uid="$(echo $inputline | cut -d '\"' -f4)"

# Option 3: For Zimbra-specific scripts (zmprov), consider:
account_id="$(echo $inputline | cut -d '\"' -f4)"

Here's a more robust version of your original script with better practices:

#!/bin/bash

while IFS= read -r inputline
do
  user_id="$(echo "$inputline" | cut -d '\"' -f4)"
  password="$(echo "$inputline" | cut -d '\"' -f8)"
  first_name="$(echo "$inputline" | cut -d '\"' -f6 | cut -d ' ' -f1)"
  last_name="$(echo "$inputline" | cut -d '\"' -f6 | cut -d ' ' -f2)"
  
  zmprov createAccount "$user_id" "$password" \
    displayName "$first_name $last_name" \
    givenName "$first_name" \
    sn "$last_name"
    
done < company.csv

• Use #!/bin/bash instead of #!/bin/sh for better compatibility
• Always quote variables to handle spaces in CSV fields
• Add error handling for CSV parsing
• Consider using awk for more complex CSV processing

Before running against production, test with:

# Dry-run mode
while IFS= read -r line; do
  user_id="$(echo "$line" | cut -d '\"' -f4)"
  echo "Would create account for: $user_id"
done < company.csv