knowledge representation

$ 4.2.20 5 176---> cat program.sh 
#!/bin/bash
# trouble: script to demonstrate common errors
number=1
if [ $number = 1 ]; then
echo "Number is equal to 1."
else
echo "Number is not equal to 1."
fi
$ 4.2.20 6 177---> sh program.sh 
Number is equal to 1.
$ 4.2.20 7 178---> 

Missing Quotes

$ 4.2.20 8 179---> cat program.sh 
#!/bin/bash
# trouble: script to demonstrate common errors
number=1
if [ $number = 1 ]; then
echo "Number is equal to 1.
else
echo "Number is not equal to 1."
fi
$ 4.2.20 9 180---> sh program.sh 
program.sh: 9: program.sh: Syntax error: Unterminated quoted string
$ 4.2.20 10 181---> 

Missing or Unexpected Tokens

$ 4.2.20 11 182---> cat program.sh 
#!/bin/bash
# trouble: script to demonstrate common errors
number=1
if [ $number = 1 ] then
echo "Number is equal to 1."
else
echo "Number is not equal to 1."
fi
$ 4.2.20 12 183---> sh program.sh 
program.sh: 6: program.sh: Syntax error: "else" unexpected (expecting "then")
$ 4.2.20 13 184---> 

Unanticipated Expansions

$ 4.2.20 14 185---> cat program.sh 
#!/bin/bash
# trouble: script to demonstrate common errors
number=
if [ $number = 1 ]; then
echo "Number is equal to 1."
else
echo "Number is not equal to 1."
fi
$ 4.2.20 15 186---> sh program.sh 
program.sh: 4: [: =: unexpected operator
Number is not equal to 1.
$ 4.2.20 16 187---> 

Note
Token (parser), usually a word or other atomic parse element.