#/bin/bash echo "This message may not be more than 8 characters" read detect How do I detect the number of letters? Would it be an IF statement?
if #detect var then else fi EDIT: How can I make it repeat until the user types a correct message?
52 Answers
You can use if-then-else-fi like this:
if [[ ${#detect} -gt 8 ]] ; then echo "Error message..." exit 1 else echo "Good to go..." exit 0 fi exit 1 generally means failure and exit 0 generally means success. In either case your script ends immediately when exit is encountered so use them appropriately.
You can also use implied if-then which is fairly unique the the shell language:
[[ ${#detect} -gt 8 ]] && { echo "Error message..." ; exit 1 ; } # successful code here exit 0 If you didn't need an error message the { ... } braces aren't required for a single command eg:
[[ ${#detect} -gt 8 ]] && exit 1 can be used to say "If the variable named detect is > 8 then exit".
Enhancing the process
Generally it is considered rude to allow the user only one chance to input a string. The polite method is to ask for the string again after telling them it needs to be 8 characters or less. For example:
echo "Enter character string 1 to 8 characters long or press <CTRL>+C to exit." while True ; do read StringVar [[ ${#StringVar} -ge 1 ]] && [[ ${#StringVar} -le 8 ]] && break echo "Sorry that string is ${#StringVar} long. Please try again." done # successful code here In this case the program keeps requesting input until variable StringVar is obtained and it is greater than or equal to 1 AND it is less than or equal to 8 at which point the while look is broken out of with the break command.
Alternately the user can press Ctrl+C/kbd> to terminate the bash script.
The concise lines:
[[ ${#StringVar} -ge 1 ]] && [[ ${#StringVar} -le 8 ]] && break echo "Sorry that string is ${#StringVar} long. Please try again." ... can be made ridiculously verbose like this:
if [[ ${#StringVar} -ge 1 ]] ; then if [[ ${#StringVar} -le 8 ]] ; then break else echo "Sorry that string is ${#StringVar} long. Please try again." continue fi else echo "Sorry that string is ${#StringVar} long. Please try again." continue fi Although not incorrect it is wasteful to both the programmer's and system's time.
I assume that you want to ask the user for input again and again until the length of input less than 8 characters. If so, you can use while loop instead of if-else statements. In that, loop will continue for infinite times until the length of input is less than 8 characters. When the length of "input" is less than 8 characters only then the script continues. The code will something like:
#!/bin/bash echo -n "Enter message with less than 8 characters: " read detect while [[ ${#detect} -gt 8 ]] do echo -n "Length of the message was greater than 8. Try again...: " read detect done echo $detect #and the rest of the code continues Moreover, if you are running the script from root (/) folder, then the shebang #!bin/bash might work (which you mentioned in the original post) but if you are running that from elsewhere, include the absolute path of the interpreter, i.e. /bin/bash, therefore modifying shebang to #!/bin/bash.
