Bash: ‘Ambiguous Redirect’ error

The aim of this page📝is to see what happens if you redirect into a file with an empty string in it.

• Lesson: in general it is always good to use double-quote for user variables to prevent things like ambiguous redirect error when values with space in it get evaluated/parsed as two strings instead of one.

1. broken code

date=$(date)
topic=$1
filename=./${topic}notes.txt
read -p "Your note:" note
echo Note '$note' saved to $filename
echo $date: $note >>$filename
  
>>> ./b13_05.sh "other things"
Your note:Note
Note $note saved to ./other thingsnotes.txt
./b13_05.sh: line 6: $filename: ambiguous redirect

2. ambiguous redirect

• bash sees the redirection in

$note >>$filename

• $filename evaluates to ./other stuffnotes.txt which, unless quoted — is ambiguous for its interpreter
• it sees it followed by multiple words with spaces between them
• this is confusing — redirection is allowed for a single file
• to fix this the variable itself has to be quoted

3. fixed code

• ✅ use quotes around user vars
• ✅ use brackets when combining symbols and literals

date=$(date)
topic="$1"
filename="./${topic}notes.txt"
read -p "Your note:" note
echo "Note '$note' saved to $filename"
echo "$date: $note" >>"$filename"

4. links

• bash — Getting an “ambiguous redirect” error