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Tag :
bash
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URL:
https://askubuntu.com/q/1198187
Title:
Bash - How to detect if a variable is more than a certain amount of characters
ID:
/2019/12/23/Bash-How-to-detect-if-a-variable-is-more-than-a-certain-amount-of-characters
Created:
December 23, 2019
Edited: June 12, 2020
Upload:
September 15, 2024
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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.