bash: comparison operator

• String Comparison
• str1 = str2
  
• str1 != str2
  
• str1 < str2
  
• str1 > str2
• -n str1 : str1 is not null
  
• -z str1 : str1 is null
• File Attribute Operator
• -a file : file exists
  
• -d file : file is a directory
  
• -e file : same as -a
  
• -f file : file is a regular file
  
• -r file : read permission
  
• -s file : file is not empty
  
• -w file : write permission
  
• -x file : execute permission
  
• -N file : modified since it was last read
  
• -O file : you own file
  
• -G file : group ID matched yours
• file1 -nt file2 : file1 is newer than file2
• file1 -ot file2 : file1 is older than file2
• Integer Conditions
• -lt : Less than
  
• -le : Less than equal
  
• -eq : Equal
  
• -ge : Greater than or equal
  
• -gt : Greater than
  
• -ne : Not equal

Refer page114, page 117 and page 121 of Learning the bash